final technical report...moody and hill (1956) first determined that the meers fault was a...
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FINAL TECHNICAL REPORT
Paleoseismic & Geophysical Evaluations to Improve Seismogenic Source Characterization of the Meers Fault, OK: Collaborative Research between
Geological Sciences, Portland State University and the Oklahoma Geological Survey, University of Oklahoma
Recipients:
Department of Geology, Portland State University PO Box 751, Portland, OR 97207-0751
Tel. (503) 725-3371
&
Oklahoma Geological Survey, University of Oklahoma 100 East Boyd St. Suite N131, Norman, OK 73019
Tel. (405) 325-8611
Principal Investigators:
Ashley R. Streig 1 & Jefferson Chang2 [email protected] 1, [email protected]
Collaborators:
Scott Bennett, Kris Hornsby, Shannon Mahan
Keywords:
Meers fault, Oklahoma; earthquake chronology and recurrence; rupture length.
Program Element III
U. S. Geological Survey National Earthquake Hazards Reduction Program Award Numbers G16AP00142 & G16AP00141
February 2018
Research supported by the U.S. Geological Survey (USGS), Department of the Interior, under USGS award numbers Award Numbers G16AP00142 & G16AP00141. The views and
conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of
the U.S. Government.
i
Award Numbers G16AP00142 & G16AP00141
Paleoseismic & Geophysical Evaluations to Improve Seismogenic Source Characterization of the Meers Fault, OK: Collaborative Research between
Geological Sciences, Portland State University and the Oklahoma Geological Survey, University of Oklahoma
Ashley R. Streig 1 & Jefferson Chang2
[email protected] 1, [email protected]
ABSTRACT
Characterizing the frequency of large earthquakes, and rupture behavior (single versus
multi-section rupture) for an intraplate fault in southwestern Oklahoma is critical to
understand how seismic hazard models for Oklahoma and the Central Eastern United
States can be improved. Earthquake frequency, rupture area and length data are
fundamental inputs for estimates of maximum earthquake magnitude and probabilistic
seismic hazard assessment. The Meers Fault is poorly understood in terms of information
such as earthquake recurrence, rupture length, and rupture area. New high resolution
topography from lidar data and new paleoseismic studies reveal that the Holocene fault
trace extends at least 6 km northwest of the previously mapped Holocene trace.
Paleoseismic results from the Meers Fault reveal at least four surface rupturing
earthquakes in the last 6,000 years, and at least two different fault rupture lengths. These
new observations have interesting implications for more than one mode of strain release
through surface fault rupture in this intraplate setting.
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TABLE OF CONTENTS Abstract ................................................................................................................................ i
1.0 Introduction .................................................................................................................. 4
1.1 Background ............................................................................................................... 4
1.2 Previous Studies ........................................................................................................ 6
2.0 Lidar fault map ............................................................................................................. 7
2.1 Southeast trace .......................................................................................................... 8
2.2 Northwest trace ......................................................................................................... 8
3.0 Paleoseismic results ................................................................................................... 12
3.1 Southeast trace ........................................................................................................ 12
3.2 Northwest trace ....................................................................................................... 14
4.0 Results ........................................................................................................................ 19
4.1 14C & OSL Sample Selection .................................................................................. 19
4.2 Southeast trace - Dog House Site Samples ............................................................. 20
4.3 Northwest trace – Water Moccasin Site Samples ................................................... 23
4.4 OxCal Models for Dog House and Water Moccasin sites ..................................... 26
5.0 Significance of results ................................................................................................ 28
6.0 Acknowledgements .................................................................................................... 28
7.0 References .................................................................................................................. 29
7.0 Publications and Conference proceedings ................................................................. 30
LIST OF TABLES
Table 1. Summary of Earthquake Evidence Dog House site ........................................... 14
Table 2. Summary of Earthquake Evidence Water Moccasin site 19
Table 3. Radiocarbon Samples from Dog House site. ..................................................... 21
Table 4. OSL Samples from Dog House site. .................................................................. 22
Table 5. Radiocarbon Samples from Water Moccasin site. ............................................. 24
Table 6. OSL Samples from Water Moccasin site. ......................................................... 25
Table 7. OxCal Model Results Dog House site. .............................................................. 26
Table 8. OxCal Model Results Water Moccasin site. ...................................................... 28
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LIST OF FIGURES
Figure 1. Location map of the Meers Fault, southwestern Oklahoma ................................ 5
Figure 2. Slope-shade Southeastern trace .......................................................................... 5
Figure 3. Offset channels along the Southeast trace ........................................................... 6
Figure 4. Lidar strip map of the Meers Fault ...................................................................... 9
Figure 5. Lidar Map of Northwest trace ........................................................................... 10
Figure 6. 1942 Orthophoto Mosaic ................................................................................... 11
Figure 7. Photomosaic trench log Dog House site ............................................................ 13
Figure 8. Water Moccasin Trench site .............................................................................. 15
Figure 9. Water Moccasin site Stratigraphic Column ....................................................... 16
Figure 10. Photomosaic trench log East wall Water Moccasin site .................................. 17
Figure 11. Photomosaic trench log West wall Water Moccasin site ................................ 18
Figure 12. OxCal model Dog House site .......................................................................... 26
Figure 13. OxCal model Water Moccasin site .................................................................. 27
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1.0 INTRODUCTION
The primary goal of this study was to improve the seismic source characterization for the northwestern and southeastern mapped sections of the Meers Fault. We employed a combination of geophysical, remote mapping, and paleoseismic techniques to improve maps of surface fault expression and the understanding of the timing of paleo-earthquakes on both the Northwest and Southeast Meers Fault sections. We conducted a detailed study combining active source seismic geophone surveys, high-resolution lidar fault mapping, paleoseismic excavations, and 14C and OSL age dating. Preliminary results from this investigation have improved information the spatial and temporal distribution of prehistoric surface rupturing earthquakes along the fault length. This report presents a new lidar derived map of the Meers Fault and results from two paleoseismic investigation sites on the Southeastern section and the poorly expressed Northwestern section of the fault. Lidar maps, paleoseismic trench logs, and age dating results for key stratigraphic units in the excavations are included in this final technical report. Geophysical study results are in progress.
1.1 Background The Meers Fault is the southwestern bounding fault along the northwest trending Frontal Wichita fault system that forms the boundary between the Wichita-Amarillo uplift to the southwest and the deep Anadarko sedimentary basin to the northeast (Harlton, 1963). The Wichita uplift coincides with the Precambrian to Early Cambrian Southern Oklahoma aulacogen, a failed rift zone that trends west-northwest across southern Oklahoma and the Texas panhandle (Budnik, 1987). The location and trend of the Frontal Wichita fault system show that modern crustal deformation is accommodated along pre-existing zones of crustal weakness (Jones-Cecil, 1995). The Meers Fault trends N60W (Figure 1), and is a reactivated fault within the failed Cambrian rift, and has left lateral-reverse sense of motion. The Meers Fault lacks historical seismicity, but has strong down to the southwest geomorphic expression and offsets Holocene deposits (Figure 2), indicating high late Quaternary slip rates greater than erosion or denudation rates (Kelson and Swan, 1990). The fault is divided into two geomorphic sections: a 37 km long southeastern section of the fault which has been the focus of multiple paleoseismic investigations and is well defined (Figure 1), and an approximately 18 km long northwestern section which is poorly constrained and the length is uncertain (Figure 1, black and orange fault sections; Crone and Wheeler, 2000). The northern 26 km of the southeastern section of the Meers Fault has a continuous linear scarp where it displaces the Post Oak Conglomerate (Figure 2; Crone and Luza, 1990). The Post Oak Conglomerate is a well-indurated limestone conglomerate that forms weathering resistant southwest-facing bedrock scarps and benches (Figure 3). The southern 9 km of this section of the fault is less conspicuous in the landscape. Here the fault occurs on the less resistant and highly erodible Hennessey Shale, which paleoseismic trenches have shown accommodates deformation by broad monoclinal folding (Hornsby, 2018; Kelson and Swan, 1990; Crone and Luza, 1990).
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Figure 1. Location map showing the Meers Fault, South-western Oklahoma. Red and Black lines are the southeastern Holocene and northwestern late Quaternary traces, respectively, from the USGS Quaternary Fault and Fold database. The Orange line is the northwest trace, found to be Holocene active, this study. Paleoseismic investigation sites in this report shown by purple triangles, used in subsequent figures. Yellow hexagons shown here and used in subsequent figures show locations of paleoseismic studies conducted in the late 1980’s through early 1990’s; 1) Valley Site, Kelson and Swan, 1990; 2) Northwestern Ponded Alluvium (PA) Site, Kelson and Swan, 1990; 3) PA and Southeastern PA sites, Crone and Luza, 1990; Kelson and Swan, 1990; 4) Canyon Creek Site, Luza et al., 1987; Crone and Luza, 1990; Kelson and Swan, 1990; 5) Browns Creek Site, Madole, 1988; 6) Saddle Mountain Creek Sites, Cetin, 1991; 1992. U & D letters denote up and downward sense of motion across the fault.
Figure 2. Slope-shade of the Southeastern Holocene active Meers Fault trace, lidar digital elevation model (DEM) derivative. This slope-shade view highlights the fault as a break in topography, shown by the linear break in slope across the landscape. Red arrows draw your eye to the break in slope along the fault. Purple triangles are DH and CC trench sites, this study. Yellow hexagons are earlier paleoseismic study sites, explanation in Figure 1.
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Figure 3. Offset channels along the Southeast trace. A) The Meers Fault offsets the Post Oak Conglomerate and forms topographic scarps, fault bound depressions, beheaded streams and deflects drainages. Blue streams in the center of the image are offset (left laterally) and elongate along the fault. Yellow hexagons are Paleoseismic sites named the Ponded alluvium and Southeastern Ponded alluvium sites of Crone and Luza, 1990; Kelson and Swan, 1990. GeoEye imagery overlain on 10m DEM. B) Dog House trench site (DH), this study. Here, alluvium ponds in the depression against the southwest facing Post Oak Conglomerate bedrock scarp. 2013 NAIP 1 meter orthophoto base.
The northwestern section of the Meers Fault has subdued geomorphic expression, the southeastern most kilometer is within Post Oak Conglomerate bedrock, and the remaining ~17 km occur on the relatively non-resistant Hennessey Shale (Figure 4; Cetin, 1991). In the northwest, the fault is expressed as very gentle, discontinuous linear breaks in slope and monocinal warping that appear to be generally aligned with the fault projection (Figure 4). Present day, this region is highly modified by roads and agricultural activities and is incised by several creeks (Figure 5). These landscape-altering factors and the subtle relief across the scarp make it difficult to decipher the tectonic signature of the fault in the landscape.
1.2 Previous Studies The Meers Fault was first mapped by Harlton (1951). Moody and Hill (1956) first determined that the Meers Fault was a Quaternary active fault based on the observation of a scarp through Quaternary alluvial surfaces. During the 1980’s, researchers excavated several paleoseismic
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trenches across the fault scarp and documented evidence of late Holocene surface rupturing earthquakes along the southeast section of the Meers Fault (Crone and Luza, 1990; Madole, 1988; Kelson and Swan, 1990). Five earlier paleoseismic investigations have been conducted on the southeastern section of the fault, and one study has been conducted on the northwestern section (Figure 1; Crone and Wheeler, 2000). Earlier paleoseismic research on the southeast section of the fault demonstrate at least two pre-historic earthquakes in the last 2,900 years and a recurrence interval of 600 to 1,700 years (Crone and Wheeler, 2000; Kelson and Swan, 1990). Paleoseismic studies on the Meers Fault suggest the late Quaternary cluster of surface rupturing earthquakes was preceded by 103 or 104 years of tectonic quiescence. The sites and event record, from northwest to southeast are (Figure 1); the Valley site yielded a two event record, the most recent event (MRE) 800 – 1600 years ago, and the penultimate between 2,000 and 2,900 years ago (Kelson and Swan, 1990). The Northwest Ponded Alluvium site yielded evidence of two events, the MRE ~ 1,050 years ago and the penultimate around ~ 1,700 years ago (Kelson and Swan, 1990). The Southeastern Ponded Alluvium site has evidence of two events, the MRE ~ 1050 years ago and the penultimate >3,400 years ago (Kelson and Swan, 1990; Crone and Luza, 1990). The Canyon Creek site (Figure 1) revealed evidence of the MRE, and evidence of the penultimate event is thought to have possibly been diffuse folding and accommodated within the Hennessey shale (Crone and Luza, 1990). The northwest section of the Meers Fault was proposed by Cetin (1991) (Figure 1). Cetin (1991) documented fault exposures in stream cuts that cross the northeast section of the Meers fault. He documented thickened soil A horizons with down on the southwest displacement. During his field study, Cetin happened upon a 50 year old irrigation ditch that crossed the fault (Cetin, 1991, pg. 28). Hand drawn logs for the irrigation ditch lack stratigraphic location information for dated charcoal samples collected for radiometric dating. The majority of stream exposures documented by Cetin (1991) contain large regions (up to 25 meters horizontally) that are covered by either vegetation or “slope material”, where many of the stratigraphic displacements are inferred to occur (Cetin, 1991). As a result of the unreproducible paleoseismic evidence outlined in Cetin (1991), the full ~18 km-long continuation of the Holocene-active Meers Fault has not been widely accepted nor included in seismic hazard assessments (Crone and Luza, 1990; Crone and Wheeler, 2003; Jones and Cecil, 1995; U.S. Geological Survey, 2006). We revisitied this irrigation ditch, cleaned the exposure and document fault displacement in the ditch. We excavated a paleoseismic trench along the adjacent alluvial surface and on trend with the N60°W fault projection. These results are presented in the Paleoseismic Results section below. 2.0 LIDAR FAULT MAP
We use lidar data and historical stereo-paired aerial photographs to map tectonic geomorphic features including the fault escarpment, linear ridges, linear depressions, aligned hillside benches, incised channels on the up-thrown block, and closed depressions with ponded alluvium on the down-thrown side of the fault (Figure 5, 6). We field checked lidar derived fault mapping to confirm that mapped fault morphologies were not anthropogenic features. Lidar data for this
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study area was collected by the Natural Resources Conservation Service (NRCS) in 2009 and 2013, the United States Geological Survey (USGS) in year 2013, and the Federal Emergency Management Agency (FEMA) in 2015.
2.1 Southeast trace We generated a fault strip map using FEMA LiDAR data for the southeastern section of the Meers fault (Figure 4A). Geologic units from a Geologic map of the Lawton 30' X 60' quadrangle, Caddo, Comanche, Cotton, Grady, Kiowa, Stephens, and Tillman Counties, Oklahoma, by T.M. Stanley and G.W. Miller. 2005. Scale 1:100,000, are overlain on a hillshade in Figure 4B.
2.2 Northwest trace Derivatives of DEMs, including hillshades with varying sun azimuth and sun altitude values, slope, curvature, and contour maps were used to detect subtle topographic surface expression of the Meers Fault (Figure 4 and 5). We document tectonic geomorphic features in Holocene surfaces along the projection of the Meers Fault ~6.1 km to the northwest of the current terminus of the Holocene trace of the fault indicated in the Quaternary fault and fold database by the U. S. Geological Survey, (2006) (see Figures 1 and 4). Topographic expression of the fault is subtle, yet relatively continuous throughout this ~6.1 km-long newly-identified Holocene-active portion of the fault, and displays southwest facing scarps. We observe increased incision of ephemeral streams on the up-thrown side (northern side) of broad monoclines as well as ponded alluvium at the base of the escarpment, immediately south of the fault (Figure 5). Evidence of lateral displacement, such as deflected drainages and offset terrace deposits along the fault are not apparent in the data. Lateral displacements of less than 2 m are not distinguishable from the sinuosity of natural meandering streams in this basin, we are not able to confirm sinistral offset reported by Cetin (1991) (Figure 5). In regions along the northwestern fault trace, the landscape has been heavily altered by anthropogenic practices, including agricultural terracing. Using georectified 1942 aerial imagery, we document a N60°W trending, southwest facing escarpment along the additional ~6.1 km-long Holocene-active fault trace identified in this study (Figure 6). In many locations, the natural landscape is better preserved and the fault scarp is more easily distinguished in the historical photomosaic than in modern lidar, 21-century topographic datasets post-date agricultural alteration of the landscape in locations (Figure 6).
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Figure 6. A) 1942 aerial photography along the southern portion of the NW section of the Meers Fault. The fault is expressed as a color lineation through the center of the image, apparent in part B. At the time of these images the landscape had undergone less anthropogenic agricultural alteration then following decades (1950 to present) time. B) Close up of the region adjacent to the Water Moccasin paleoseismic site. A Two red arrows point to a NW trending color lineation near the center of the photo this coincides with a broad N60°W trending monocline and agrees with the fault morphology observed with a bare earth lidar DEM.
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3.0 PALEOSEISMIC RESULTS Paleoseismic trench locations were surveyed using a handheld Trimble GeoXH Differential GPS unit. We scraped backhoe polish from vertical walls to clean trench exposures, measured and leveled a nail grid on the trench walls, photographed, and stitched photos into a photomosaic using Structure from Motion 3D imaging software (Agisoft). We made detailed maps of the exposures on field prints of the photomosaic logs, and described all stratigraphic units exposed within the trenches. Additionally, we collected organic material, including seeds and detrital charcoal for radiocarbon dating and logged the location of these samples on field logs. We collected samples for optically stimulated luminescence (OSL) dating, and recorded these sample locations. We also collected bulk samples of key stratigraphic units for later laboratory analysis and separation of organics. We examined radiocarbon samples under a binocular scope, photographed and described the samples prior to submission for dating.
3.1 Southeast trace Dog House Paleoseismic Site Near the northern end of the Southeast section of the fault, in the Slick Hills we excavated a 2.5’ wide slot trench at a new investigation site, located within a linear valley along a deflected drainage. (Figure 1, Figure 3). The site is located a few kilometers from the Ponded alluvium sites of Crone and Luza (1990) and Kelson and Swan (1990) (Figure 1, Figure 3). Here, the fault offsets Post Oak Conglomerate and forms strong southwest facing scarps. Alluvium has accumulated in the linear depression and is deposited against the fault scarp (Figure 3). The trench exposed bedrock on the northeast side of the fault and alluvial units on the southeast. The DH trench totaled 14 meters length, including ramps into the trench, reached a maximum depth of 3 meters and was secured with hydraulic shores (Figure 7). On the northeast side of the fault, altered Post Oak Conglomerate bedrock was exposed at the base of the trench. Overlying this is unit 200, a normally graded, clast supported, gravel. Unconformably overlying unit 200, northeast and away from the fault, is unit 30, a sequence of finely laminated sandy silt interbeds with 2-3 cm thick soil A horizon development on each silt interbed. The silts have a sharp, erosional basal contact with the underlying gravels. Overlying this is Unit 10, a massive silt with minor angular pebbles and sand, and modern AB soil development. This unit is laterally continuous across the trench (Figure 7). Stratigraphy southeast of the fault differs from the northeast. Here, bedrock was not encountered in the base of the trench. Fine-grained alluvial and tapering scarp derived colluvial units are mapped to a depth of ~ 3m below the ground surface. Unit 90 is the deepest unit exposed, this is a buried soil, massive silt with 1mm wide CaCO3 stringers. Overlying this is unit 80, massive silt, scarp derived colluvium tapers to the southwest and pinches out against the soil developed on unit 90. Unit 70 is stratigraphically above unit 80, it is a massive silt with buried soil development in the upper 15 cm. Unit 70 thins to the southwest, away from the fault. Unit 60 is a gravelly silt tapers to the southwest over ~ 1 meter and pinches out against the top of unit 70. Unit 60 is interpreted to be a scarp derived colluvium. Unit 50 is a massive silt, overlies units 60 and 70, and thickens away from the fault. Unit 40 is massive silt with angular gravels along the basal 3cm. Unit 40 overlies unit 50, and is laterally discontinuous to the southeast where it has a
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diffuse contact with underlying unit 50. Unit 20 is massive silt, and occurs southwest of the fault and is stratigraphically above unit 40 (Figure 7).
Figure 7. A) Photomosaic trench log, West wall, 2016 Dog House Trench. 2.5’ wide slot trench, gray rectangles are hydraulic shores. B) Interpreted trench log, West wall, 2016 Dog House Trench. Faults are red, stratigraphic horizons are multicolored, many are truncated by the fault. Earthquake horizons 1 - 3 are highlighted by blue text.
Dog House Site Interpretations This site yielded evidence of at least three surface rupturing earthquakes, earthquake horizons are labeled E1 through E3. Here, surface fault rupture appears to generate a free face of the Post Oak Conglomerate as a southwest facing scarp that collapses and forms scarp derived colluvium on the event horizon ground surface. Two of the three earthquakes identified generated scarp-derived colluvial deposits (units 60 & 80), while the most recent earthquake, E1, faulted these deposits and extends upward into higher stratigraphic units (units 40 & 50) (Figure 7). Scarp derived colluvial units are shown as blue polygons on the trench log, these deposits are stratigraphically above the earthquake horizons which are labeled E2 and E3. Earthquake 2 occurred when unit 70 was at the ground surface, E3 occurred while unit 90 was the ground
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surface. OSL and 14C samples from these units constrain the timing of these surface rupturing earthquakes, samples are shown in Table 2 and Table 3. Our 2016 slot trench (Figure 3), reached maximum allowable depths for a slot trench excavation, and yielded a record of three earthquakes within 2.5 m of the ground surface. The trench did not extend to bedrock on the footwall (down-thrown) side of the fault (Figure 7). We interpret the thick section of sediment on the down-thrown side of the fault to represent vertical separation of bedrock greater than 2.5 meters across the fault, and this site records > 3 events. Table 1. Summary of earthquake evidence for the Dog House trench (Meers Fault, OK) and earthquake timing constrained by the Oxcal Bayesian statistical age model shown in Figure 12.
3.2 Northwest trace Water Moccasin Paleoseismic Site In the northwest, complex surface deformation includes fault splays, a left step, monoclinal warping, and a minor change in fault strike that contributes to its subtle surface expression (Figure 8). The fault is expressed by linear escarpments, incised channels on the upthrown side of the scarp, and closed depressions on the downthrown side (Figure 5). We examined the northwestern scarp in a paleoseismic excavation at the Water Moccasin site (Figure 1, 8) where weathered Permian Hennessey Shale and a ~1–2 m-thick veneer of Holocene alluvial deposits have been deformed during three surface-folding earthquakes (Figure 9, 10, 11) (Hornsby, 2017). We document monoclinal warping of Holocene alluvial deposits and weathered Permian Hennessey Shale bedrock with 1-2 meters of relief (Figure 11 grid meters V6-V12). The highest folded alluvial deposits are onlapped by undeformed, massive, sandy silts with moderate soil development, which are in turn overlain by modern fill deposits (Figure 10, 11). In Figure 10 and 11B the shale is purple, folded alluvial units range from tan to pink (on the interpreted log), and on-lapping to overlapping alluvial sediments which post-date the most recent earthquake (MRE) are shown on the log as shades of brown to gray (Hornsby, 2017). Earthquake horizons are shown as red lines. In an adjacent irrigation ditch exposure these units are faulted near the
EventEvent
Horizon Earthquake Evidence
Modeled Event Timing (yrs BP) (2σ)
DH E1 50 & 200 Upward fault terminations within unit 50Unit 200 in vertical fault contact with unit 50 & 60 along vertical fault.
Unit 40 caps both the vertical and SW dipping fault, and angular gravels at the base of this unit are sourced by the gravel on the up-thrown side of the fault.
DH E2 70 Colluvial wedge, unit 60 stratigraphically overlies unit 70 soil.DH E1 truncates NE margin of unit 60. Colluvial wedge unit 60 formed before MRE.
Colluvial wedge, unit 80 stratigraphically overlies unit 90 soil.DH E3 Down-on-the-SW displacement of unit 90 soil within 1.5 m of the vertical fault
Thickening of unit 70 within 1.5m of the freescarp at the vertical fault, infilling rupture generated releif.
South dipping fault in bedrock and unit 200 drops gravel unit 200 down to the southwest
723-1447
1424-1906
2765-3634
15
surface (Figure 8C). AMS C14 dates from of detrital charcoal, and OSL dates of sandy alluvial stratigraphy indicate two earthquakes occurred since 6 ka and one event prior to 6 ka.
Figure 8. A) Slope-shade site map from lidar for the WM site showing the fault scarp (dashed red lines), the trench footprint (purple polygon), the seismic survey (yellow line), the irrigation ditch exposure (green line), the topographic profile (black line). Ephemeral stream channels are shown in blue. Locations of XX and YY were surveyed using a differential GPS. B) Topographic profile with 0.21 m of vertical surface offset across the scarp. C) Fault relationships exposed in the southeast wall of the irrigation ditch. Hennessey Shale (HS) is in fault contact with fault-derived colluvium (CT2) that consists of silt to gravel up to 1 cm. Silt units are located above these units and are partially covered by a recent slump deposit from tree throw. After cleaning the exposure, the sharp fault contact is visible across the floor of the ditch and on the northwestern wall of the ditch floor and is oriented N25°W (see short red line in A).
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Figure 9. Stratigraphic column of units exposed in the Water Moccasin trench and irrigation ditch. The oldest unit exposed is Permian Hennessey Shale bedrock. This is overlain by fine-grained alluvial units ranging from silt, silty-clay, to fluvial gravels. Lithologies are shown in stratigraphic order with youngest at the top, oldest at the bottom of the column.
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inty
. Uni
t 5, P
erm
ian
bedr
ock
is o
verla
in b
y a
1-2
m o
f Hol
ocen
e al
luvi
al se
dim
ents
.
18
Figu
re 1
1. W
ater
Moc
casi
n tre
nch,
wes
t wal
l. A
) 1 m
by
1 m
grid
pho
tom
osai
c lo
g. V
ertic
al g
rey
rect
angl
es a
re h
ydra
ulic
sho
res.
B) I
nter
pret
ed
trenc
h lo
g w
ith s
tratig
raph
ic u
nits
and
infe
rred
ear
thqu
ake
horiz
ons
(thic
k re
d lin
es).
On-
lapp
ing
to o
verla
ppin
g st
ratig
raph
y hi
ghlig
ht m
onoc
linal
fo
ld d
efor
mat
ion,
and
infil
ling
agai
nst f
ault
gene
rate
d to
pogr
aphi
c re
lief.
Age
det
erm
inat
ion
sam
ple
loca
tions
sho
wn
as s
mal
l squ
ares
with
mea
n ag
e an
d 2σ
unc
erta
inty
. Uni
t 5, P
erm
ian
bedr
ock
is o
verla
in b
y a
1-2
m o
f Hol
ocen
e al
luvi
al se
dim
ents
.
19
Water Moccasin Site Interpretations We find clear evidence for two surface deforming earthquakes at the Water Moccasin site, and less certain evidence for one earlier event. Evidence for these events are compiled in the table below (Table 2). Table 2. Summary of earthquake evidence documented in the Water Moccasin trench (Meers Fault, OK) and earthquake timing constrained by the Oxcal age model shown in Figure 13.
4.0 RESULTS
4.1 14C & OSL Sample Selection Organic samples were collected from trench exposures for 14C Accelerated Mass Spectrometry (AMS) dating. These materials included detrital charcoal and seeds. Bulk sediment samples were collected for later laboratory separation of datable material. Bulk samples were collected from each unit and sample locations were mapped on trench logs. Sediment samples were sonicated or wet-seived in the lab to separate organics from sediment. All organic samples were ranked for
4702-3108 cal. years BP
6152-5550 cal. years BP
3. Fluvial deposits (Unit 3) are folded and tilted, these are more deformed than overlying strata.
4. Faulting in the irrigation ditch: faulted gravels above Hennessey Shale are believed to be similar to unit 2g in the WM trench. Scarp derived colluvium is inferred to be Holocene here.
Event Event Horizon Earthquake Evidence
Modeled Event
Timing (2σ)
3. Uplift of channel gravel depoists (unit 2a) above overbank flood deposits.
Ante-Penultimate
(E3?)
Penultimate (E2)
MRE (E1)
Erosional Unconformity
cut across Hennessey
Shale
3, 4A, 4B
2A, 2D
~9598- cal. years BP -Permian
1. Monoclinal folding of units 2a-2f
2. Fluvial deposits are eroded and truncated by a high energy fluvial deposit (unit 2g) that is following the topographic low across the scarp created by the penultimate earthquake.
2. Onlapping to overlapping massive silts that have soil development (units 1a- 1c) infill relief across the scarp.
1. Erosion of the fault scarp (unit 4) and deposition of a colluvial wedge (unit 2h).
1. A topographic low may have existed at the base of the modern escarpment and localized the deposition of unit 3. This depression is coincident with the fold zone, and may have been created tectonically or simply by erosion.
20
14C analysis based on; the sample type (e.g. seed, or charcoal), amount of material, and the location within the stratigraphic unit from which they were recovered. We collected two to three sediment samples for Optically Stimulated Luminescence (OSL) dating from each paleoseismic site. OSL is an ideal dating method for sandy, quartz-rich deposits that lack organic content. Luminescence dating provides an estimate of the time of deposition of a unit, determined by the last exposure of sunlight to sand grains (Gray et al. 2015). The basic principle relies on the ability of quartz and feldspar crystal lattices to absorb and store free electrons that accumulate after burial from the ambient background radiation (ionizing energy) generated by radioisotopes in surrounding sediments (Gray et al., 2015; Rittenour, 2008). OSL samples were analyzed by Shannon Mahan at the USGS Luminescence Dating Laboratory. We use OxCal software to develop age models for each paleoseismic site with both 14C and OSL age results. OxCal (Bronk-Ramsey, 2009) calibrates 14C ages using the IntCal13 carbon atmospheric curve (Reimer et al., 2013), and uses stratigraphic ordering information and Bayesian statistics to better constrain unit ages based on relative age information (after Lienkaemper and Bronk-Ramsey, 2009). PSU Graduate student, Kris Hornsby, created an OxCal statistical age model (Bronk-Ramsey, 2009) for the Water Moccasin site that incorporates radiocarbon age results, OSL age results, and unit depth.
4.2 Southeast trace - Dog House Site Samples Radiocarbon (14C) Dating Macro-charcoal was abundant in the highest two stratigraphic units (unit 10, 20a, 20b), and sparse in deeper sedimentary units. These samples were collected in the field. We selected ten detrital charcoal samples for 14C AMS dating, five of these were incorporated in our final age model (Figure 12). Sample information, stratigraphic unit the sample was collected from, depth of sample, and calibrated sample ages are shown in Table 3. Optically Stimulated Luminescence (OSL) Dating We collected two OSL samples to further constrain the age of the stratigraphic section exposed in the excavation (Table 4). Sample DH_1_16_L02 was collected from unit 200 gravels. Sample DH_1_16_L01 was collected from unit 30,a sequence of interbedded silts and fine sand northeast of the fault. Results from sample DH_1_16_L02 in unit 200 gravels was incorporated in our final age model (Figure 12).
21
Unm
odel
edDe
pth
belo
wCA
MS
#Sa
mpl
ed13
Cfra
ctio
n ±
D14C
±14
C ag
e±
Calib
rate
d Ag
e%
Mod
eled
Age
%Ag
reem
ent
Stra
tigra
phic
grou
nd s
urfa
ceNa
me
Mod
ern
(yrs
BP)
(yrs
BP)
Inde
xU
nit
(cm
)
1777
09D
H1_
16_R
C17
-25
0.90
510.
0047
-94.
94.
780
045
665-
795
95.4
668-
791
95.4
100.
910
4017
7711
DH
1_16
_RC
19-2
50.
7565
0.00
28-2
43.5
2.8
2240
3021
54-2
339
95.4
3065
1777
13D
H1_
16_R
C21
*-1
3.9
0.80
200.
0023
-198
.02.
317
7525
1529
-169
395
.430
7017
7710
DH
1_16
_RC
18-2
50.
8253
0.00
29-1
74.7
2.9
1545
3013
72-1
526
95.4
1370
-152
695
.498
.940
80
1777
07D
H1_
16_R
C13
-25
0.78
660.
0049
-213
.44.
919
3050
1737
-199
195
.417
39-1
996
95.4
100.
660
90
1777
08D
H1_
16_R
C14
-25
0.72
430.
0065
-275
.76.
525
9080
2380
-285
995
.423
82-2
857
95.4
100.
660
135
1777
14D
H1_
16_R
C28
-25
0.71
770.
0030
-282
.33.
026
6535
2745
-284
695
.427
45-2
844
95.4
100.
560
130
1777
12D
H1_
16_R
C20
-25
0.93
110.
0043
-68.
94.
357
540
525-
653
95.4
5085
1777
15D
H1_
16_R
C26
*-1
4.2
0.82
170.
0025
-178
.32.
515
7525
1406
-153
295
.410
65
1) d
13C
val
ues
are
the
assu
med
val
ues
acco
rdin
g to
Stu
iver
and
Pol
ach
(Rad
ioca
rbon
, v. 1
9, p
.355
, 197
7) w
hen
give
n
w
ithou
t dec
imal
pla
ces.
Val
ues
mea
sure
d fo
r the
mat
eria
l its
elf a
re g
iven
with
a s
ingl
e de
cim
al p
lace
.
S
ampl
es w
ith a
n (*
) wer
e la
rge
enou
gh, a
nd a
s re
ques
ted,
to ta
ke a
sam
ple
spec
ific
split
for I
RM
S d
13C
ana
lysi
s.
2) T
he q
uote
d ag
e is
in ra
dioc
arbo
n ye
ars
usin
g th
e Li
bby
half
life
of 5
568
year
s an
d fo
llow
ing
the
conv
entio
ns o
f Stu
iver
and
Pol
ach
(ibid
.).3)
Rad
ioca
rbon
con
cent
ratio
n is
giv
en a
s fra
ctio
n M
oder
n, D
14C
, and
con
vent
iona
l rad
ioca
rbon
age
.
4) S
ampl
e pr
epar
atio
n ba
ckgr
ound
s ha
ve b
een
subt
ract
ed, b
ased
on
mea
sure
men
ts o
f sam
ples
of 14
C-fr
ee c
oal.
B
ackg
roun
ds w
ere
scal
ed re
lativ
e to
sam
ple
size
.
5) S
ampl
e D
H1_
16_R
C12
did
not
pro
vide
eno
ugh
carb
on fo
r a re
liabl
e an
alys
is.
Tabl
e 3
. Rad
ioca
rbon
Sam
ples
from
the
Dog
Hou
se P
aleo
seis
mic
site
.
22
Sam
ple
% W
ater
K
(%)b
U (p
pm)b
Th
(ppm
)bT
otal
Dos
eE
quiv
alen
t nd
Scat
tere
Age
info
rmat
ion
cont
enta
(Gy/
ka)c
Dos
e (G
y)(y
rs)e
DH
1-16
-L01
5 (4
3)1.
38 ±
0.0
53.
20 ±
0.1
812
.2 ±
0.3
92.
95 ±
0.0
741
.9 ±
3.7
5 (2
5)27
%14
,200
± 1
,300
min
imum
age
64.3
± 3
.925
(25)
27%
21,8
00 ±
1,4
30ce
ntra
l age
DH
1-16
-L02
1 (1
9)0.
40 ±
0.0
61.
12 ±
0.2
23.
43 ±
0.3
61.
09 ±
0.0
93.
87 ±
0.2
83
(30)
85%
3,55
0 ±
380
min
imum
age
11.1
± 1
.828
(30)
85%
10,1
80 ±
1,8
40ce
ntra
l age
a Fiel
d m
oist
ure,
with
figu
res
in p
aren
thes
es in
dica
ting
the
com
plet
e sa
mpl
e sa
tura
tion
%.
Dose
rate
s ca
lcul
ated
usi
ng 2
5% o
f the
sat
urat
ed m
oist
ure
(i.e.
4 (4
8) =
48
* 0.2
5 =
12).
b Ana
lyse
s ob
tain
ed u
sing
hig
h-re
solu
tion
gam
ma
spec
trom
etry
(hig
h pu
rity
Ge
dete
ctor
).c In
clud
es co
smic
dos
es a
nd a
ttenu
atio
n w
ith d
epth
cal
cula
ted
usin
g th
e m
etho
ds o
f Pre
scot
t and
Hut
ton
(199
4).
Cosm
ic d
oses
wer
e 0.
16-0
.20
Gy/
ka.
d Num
ber o
f rep
licat
ed e
quiv
alen
t dos
e (D
E) e
stim
ates
use
d to
cal
cula
te th
e eq
uiva
lent
dos
e. F
igur
es in
par
enth
eses
indi
cate
tota
l num
ber o
f mea
sure
men
ts in
clud
ed in
cal
cula
ting
the
repr
esen
ted
D E a
nd a
ge u
sing
the
min
imum
age
mod
el (M
AM
); an
alyz
ed v
ia s
ingl
e al
iquo
t reg
ener
atio
n on
qua
rtz g
rain
s.e De
fined
as
"ove
r-di
sper
sion
" of t
he D
E v
alue
s. V
alue
s >3
0% a
re c
onsi
dere
d to
be
poor
ly b
leac
hed
or m
ixed
sed
imen
ts.
f Dose
rate
and
age
for f
ine-
grai
ned
250-
90 m
icro
n si
zed
quar
tz.
Expo
nent
ial +
linea
r fit
used
on
equi
vale
nt d
ose,
err
ors
to tw
o si
gma
on a
ge a
ll oth
ers
are
one
sigm
a.
Tab
le 4
. Q
uartz
-Opt
ical
ly st
imul
ated
lum
ines
cenc
e (O
SL) a
ge re
sults
for t
he D
og H
ouse
tren
ch (M
eers
Fau
lt, O
klah
oma)
.
23
4.3 Northwest trace – Water Moccasin Site Samples Radiocarbon (14C) Dating Trench sediments yielded little organic material for radiocarbon (14C) dating. The majority of the samples collected from the trench walls believed to be microcharcoal were later determined to be iron oxide nodules after examination under a binocular microscope. Only four of the 11 microcharcoal samples selected from bulk sediment samples sizes survived the pre-treatment process of acid and base rinses. Most samples were of insufficient mass after pre-treatment (< 0.001 g) for radiocarbon analysis. Radiocarbon ages for trench samples were calibrated to the 14C curve (Reimer et al., 2016) and are listed with 2-sigma uncertainty as follows: unit 3, 9680-9520 cal. yrs. BP (±2σ); unit 4b, 6218-5966 cal. yrs. BP (±2σ); unit 2f, 4832-4624 cal. yrs. BP (±2σ); and the base of unit 1c, 3167-2971 cal. yrs. BP (±2σ) (Table 5). Optically Stimulated Luminescence (OSL) Dating Two samples were collected from fluvial unit 2g and 2a for OSL analysis. Unit 2g yielded a laboratory age of 7160 ± 1200 BP and unit 2a yielded an age of 5620 ± 580 BP, with two sigma uncertainty (Table 6). A common concern with OSL dating in fluvial environments is the potential for partial bleaching (incomplete resetting), resulting in artificially old burial ages (Gray et al., 2015). The preliminary age results were much older than the ages reported here (see Hornsby, 2017 for full details), and partial bleaching was suspected. Therefore, abundant (> 50) aliquots were processed by Shannon Mahan at the USGS Luminescence Dating Laboratory to identify a more representative age signal from several bleached grains (see ‘minimum age’ in Table 6).
24
Tabl
e 5.
Acc
eler
ator
mas
s spe
ctro
met
ry (A
MS)
radi
ocar
bon
age
resu
lts fr
om th
e W
ater
Moc
casi
n tre
nch
(Mee
rs F
ault,
Okl
ahom
a).
WM
-16-
RC
15A
MS
RC
B
eta-
4492
2129
30 ±
30
3167
-297
4-2
3.6
1c1.
52M
acro
char
coal
WM
-06
AM
S R
C
PR
I-554
441
79 ±
24
4832
-462
4-2
1.03
2f2.
58M
icro
char
coal
W
M-1
6A
MS
RC
P
RI-5
545
5229
± 2
562
18-5
966
-22.
774b
2.82
Mic
roch
arco
al
WM
-9A
MS
RC
P
RI-5
705
8609
± 4
096
80-9
520
-22.
673
1.63
Mic
roch
arco
al
WM
-16-
RC
5A
MS
RC
B
eta-
4492
212D
1.83
Mac
roch
arco
alW
M-0
1-01
AM
S R
C
Bet
a-44
9222
4C3.
02M
acro
char
coal
WM
-06-
01A
MS
RC
B
eta-
4492
232F
2.58
Mac
roch
arco
alW
M-0
7-01
AM
S R
C
Bet
a-44
9224
4B3.
03M
acro
char
coal
WM
-20-
01A
MS
RC
B
eta-
4492
254C
3.42
Mac
roch
arco
alW
M-0
5A
MS
RC
P
RI-5
706
2D2.
04B
ulk
Sed
imen
tC
T-02
AM
S R
C
PR
I-570
4Irr
igat
ion
Ditc
h (C
T2)
~1.5
Bul
k S
edim
ent
a S
ampl
es a
re li
sted
in s
tratig
raph
ic o
rder
and
loca
tions
are
sho
wn
in (F
igur
e 10
,11,
12 )
c T
he re
porte
d ag
e is
in ra
dioc
arbo
n ye
ars
usin
g th
e Li
bby
half-
life
of 5
568
year
s an
d fo
llow
ing
the
conv
entio
ns o
f Stu
iver a
nd P
olac
h [1
977]
; unc
erta
inty
sho
wn
is
±1σ.
RC
YB
P is
the
radi
ocar
bon
year
s be
fore
pre
sent
age
prio
r to
calib
ratio
n to
the 1
4 C c
urve
.
b In
itial
sam
ple
prep
erat
ion
and
sele
ctio
n w
as d
one
at P
ortla
nd S
tate
Uni
vers
ity. R
adio
carb
on (R
C) s
ampl
es w
ere
prep
ared
and
sep
erat
ed a
t Pal
eoR
esea
rch
Inst
itute
, Inc
.(PR
I), B
eta
Ana
lytic
Inc.
, and
The
Nat
iona
l Oce
an S
cien
ces
Acc
eler
ator
Mas
s S
pect
rom
etry
(NO
SA
MS
) fac
ility
.
Stra
tigra
phic
Uni
t
Dep
th
Bel
ow
Gro
und
Surfa
ce (m
)
Mat
eria
l δ1
3C (‰
)Sa
mpl
e C
odea
Anal
ytic
al
Met
hodb
Lab
Cod
e
14C
Age
±
1σ,
RC
YBPC
Cal
ibra
ted
Age
Ran
ge ±
2σ
, yea
rs
B.P
.
Sam
ples
Fai
led
(Insu
ffici
ent
Mas
s fo
r Rad
ioca
rbon
An
alys
is)
25
Tab
le 6
. Q
uartz
-Opt
ical
ly st
imul
ated
lum
ines
cenc
e (O
SL) a
ge re
sults
from
the
Wat
er M
occa
sin
trenc
h (M
eers
Fau
lt, O
klah
oma)
.
Tota
l Dos
e (G
y/ka
)c
9.23
± 0
.59
3 (4
8)62
%7,
160
± 1,
200
min
imum
age
29.4
± 2
.745
(48)
62%
22,7
90 ±
4,8
80ce
ntra
l age
7.03
± 0
.45
4 (3
6)54
%5,
620
± 58
0m
inim
um a
ge13
.9 ±
1.4
33 (3
6)54
%11
,120
± 2
,520
cent
ral a
ge
c In
clud
es co
smic
dos
es a
nd a
ttenu
atio
n w
ith d
epth
cal
cula
ted
usin
g th
e m
etho
ds o
f Pre
scot
t and
Hut
ton
(199
4).
Cos
mic
dos
es w
ere
0.16
-0.2
0 G
y/ka
.
Sam
ple
Nam
eAg
e In
form
atio
n Ag
e (Y
ears
BP)
f
d N
umbe
r of r
eplic
ated
equ
ivale
nt d
ose
(DE) e
stim
ates
use
d to
cal
cula
te th
e eq
uiva
lent
dos
e. F
igur
es in
par
enth
eses
indi
cate
tota
l num
ber o
f mea
sure
men
ts in
clud
ed in
cal
cula
ting
the
repr
esen
ted
DE
and
age
usi
ng th
e m
inim
um a
ge m
odel
(MA
M);
anal
yzed
via
sin
gle
aliq
uot r
egen
erat
ion
on q
uartz
gra
ins.
K (%
)bU
(ppm
)bTh
(ppm
)bEq
uiva
lent
Do
se (G
y)
ndSc
atte
re%
Wat
er
cont
ent a
b A
naly
ses
obta
ined
usi
ng h
igh-
reso
lutio
n ga
mm
a sp
ectro
met
ry (h
igh
purit
y G
e de
tect
or).
1.29
± 0
.07
1.25
± 0
.07
3.00
± 0
.32
2.88
± 0
.19
0.39
± 0
.03
4 (2
0)
2 (1
7)0.
37 ±
0.0
32.
22 ±
0.1
62.
50 ±
0.2
3
WM
-16-
L01
WM
-16-
L02
a Fi
eld
moi
stur
e, w
ith fi
gure
s in
par
enth
eses
indi
catin
g th
e co
mpl
ete
sam
ple
satu
ratio
n %
. D
ose
rate
s ca
lcul
ated
usi
ng 2
5%
of th
e sa
tura
ted
moi
stur
e (i.
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26
4.4 OxCal Models for Dog House and Water Moccasin sites Southeast trace - Dog House Site Age Model We document evidence for three surface rupturing earthquakes, probability distribution functions (pdf’s) for these event ages are modeled posterior distributions using Oxcal 4.3 (Bronk Ramsey, 2018). Of the ten detrital charcoal samples selected for 14C AMS dating, only five yielded ages that were stratigraphically consistent, and one OSL sample was stratigraphically relevant to this age model. We find DH-E1 occurred between 723-1447 yrs BP, DH-E2 occurred between 1424-1906 yrs BP, and DH-E3 occurred between 2765-3634 years BP (Figure 12, Table 7).
Figure 12. OxCal model results for the Dog House trench. Carbon and OSL ages are shown as gray probability distribution functions (pdf’s). Calibrated 14C calendar ages using Reimer et al., 2013 calibration curve, and modeled ages with 1σ and 2σ uncertainty. (Oxcal; Bronk Ramsey, 2018).
Table 7. OxCal Modeling Results Dog House Site
Sample/Earthquake Unit Calibrated age (years BP) Modeled (years BP) A*(95.4%) (95.4%)
DH1_16_RC17 10 665-795 668-791 100.9E1 723-1447
DH1_16_RC18 40 1372-1526 1370-1526 98.9E2 1424-1906
DH1_16_RC13 60 1737-1991 1739-1996 100.6DH1_16_RC14 60 2380-2859 2382-2857 100.6DH1_16_RC28 60 2745-2846 2745-2844 100.5
E3 2765-3634N DH_OSL2 200 3170-3930 3204-3921 102.2
* A is the individual agreement index, which indicates how well each sample agrees with the overlying and underlying stratigraphic age results.
723 – 1447 (2σ)
1424 – 1906 (2σ)
2765 – 3634 (2σ)
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Northwest trace - Water Moccasin Site Age Model The Water Moccasin site revealed monoclinal fold deformation for at least two surface deforming earthquakes (Figure 13). Age dating reveals 2 events in the last 6,000 years, the longest earthquake record on the fault. Pdf’s for these event ages are modeled using Oxcal software (Bronk Ramsey, 2018). Pdf’s are broad as a result of the small abundance of datable material recovered from stratigraphic deposits. We find that WM-E1 occurred between 4702-3108 years BP, WM-E2 occurred between 6152-5550 years BP (Figure 13, Table 8).
Figure 13. Oxcal Bayesian statistical model of OSL and calibrated 14C ages modeled to constrain the ages of Holocene earthquakes (E1 and E2) observed in the Water Moccasin trench (Meers Fault, Oklahoma). Model results are based on stratigraphic ordering of trench units. Light gray probability distribution functions (pdfs) are ‘prior' distributions, dark gray pdf’s are ‘posterior’ distributions constrained by ordering information (see Bronk-Ramsey (2009) and Lienkaemper and Brock-Ramsey, 2009 for details of this method). Earthquake timing pdf’s for E1 and E2 are calculated from the modeled posterior distributions.
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Table 8. OxCal Modeling Results Water Moccasin Site OxCal Modeling Results Water Moccasin Site
Sample/Earthquake Unit Unmodeled (years BP) (95.4%)
Modeled (years BP) (95.4%) A*
WM_16_RC15 1c 3169-2974 3168-2975 99.6 MRE (E1) 4702-3108 WM_B6 2f 4831-4625 4832-4626 100
WM_16_OSL2 2a 6200-5040 5844-4997 100.9 WM_17_OSL1 2g 8360-5960 6035-5315 9.1
Penultimate (E2) 6152-5550 WM_B16 4b 6170-5919 6175-5921 90.8 WM_B9 3 9672-9524 9670-9522 101.3
* A is the individual agreement index, which indicates how well each sample agrees with the overlying and underlying stratigraphic age results. 5.0 SIGNIFICANCE OF RESULTS
During 2016 we excavated three paleoseismic trenches and documented evidence for 2 – 3 surface rupturing earthquakes at each site. On the Southeast section of the fault, at the DH site, we identify three surface rupturing earthquakes in the last ~3,600 years. The DH trench did not extend to bedrock on the footwall (down-thrown) side of the fault. We interpret vertical separation of bedrock greater than 2.5 meters across the fault and potential for a longer record. The Northwest WM site yielded evidence for two surface deforming events in the last 6,000 years, the longest earthquake record on the fault to date. During our 2016 investigation we documented broad wavelength accommodation of vertical displacements in the Hennessey Shale in the Northwest section of the fault, and extend the Holocene active trace 6.1 km to the northwest. Broad monoclinal folding in the Hennesy shale may explain why the Meers fault was difficult to map and identify in the northwest region prior to lidar datasets. We find that the Southeast section has ruptured independent of the Northwest section at least twice in the last ~ 2,000 years (DH-E1 & E2). Timing of earthquake DH-E3 on the southeast section of the fault overlaps in age with the most recent surface deforming event on the Northwest trace of the fault. We find that the Northwest section of the fault ruptures with the Southwest section of the fault. 6.0 ACKNOWLEDGEMENTS
We would like to thank Kimbell Ranch and Dean Reeder, for granting us access to their property for mapping and paleoseismic excavations. We greatly appreciate Tom Cavenagh for all his help and hard work, and for inspiring conversations on local geology and life. We especially loved the opportunity he gave us to fly over the fault and our open trenches! We thank Issac Woelfel, John Schwing, Noor Ghouse, Stephen Holloway from the Oklahoma Geological Survey for their assistance in the field, and logistical support.
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We use lidar data collected by the NRCS and FEMA for this study from USGS 3DEP, https://nationalmap.gov/3DEP/. OSL samples were run by Shannon Mahan, GECSC: USGS Luminescence Dating Laboratory. 14C samples were run by Tom Guilderson, Lawrence Livermore National Laboratory – Center for Accelerated Mass Spectrometry. 7.0 REFERENCES Baker, E.M., Holland A.A., 2013, Probabilistic Seismic Hazard Assesment of the Meers Fault,
Southwestern Oklahoma: Modeling and Uncertainties, Oklahoma Geological Survey Special Publication SP2013-02.
Budnik, R. T., 1987, Late Miocene reactivation of Ancestral Rocky Mountains structures in the Texas Panhandle: a response to Basin and Range extension:Geology, 15, pp. 163-166.
Bronk Ramsey, C., 2018, OxCal Program, v.4.3: Radiocarbon Accelerator Unit, University of Oxford, Oxford, United Kingdom, https://c14.arch.ox.ac.uk/oxcal.html (last accessed 2/5/2018).
Bronk Ramsey, C., 2009, Bayesian analysis of radiocarbon dates: Radiocarbon, 51, 1, p. 337-360. Bronk-Ramsey, C., 2009, Dealing with Outliers and Offsets in Radiocarbon Dating: Radiocarbon,
v. 51, p. 1023–1045, doi: 10.1017/s0033822200034093. Bronk-Ramsey, C. (1995). Radiocarbon Calibration and Analysis of Stratigraphy: the OxCal
Program. Radiocarbon, 37(2), 425–430. http://doi.org/10.2458/rc.v37i2.1690 Calais, E., T. Camelbeeck, S. Stein, M. Liu, and T. J. Craig (2016), A new paradigm for large
earthquakes in stable continental plate interiors, Geophys. Res. Lett, 43, doi:10.1002/2016GL070815.
Cetin, H., 1991, The Northwest Extension of the Meers Fault in Southwestern Oklahoma, Texas A&M University, Masters Thesis, 89 pages.
Cetin, H. (1998). Near-surface folding along an active fault: seismic or aseismic? Tectonophysics, 292(3–4), 279–291. http://doi.org/10.1016/S0040-1951(98)00074-2
Crone., A.J., and Luza, K.V., 1990, Style and timing of Holocene surface faulting on the Meers fault, southwestern Oklahoma, Geological Society of America, 102, no. 1, p. 1-17.
Crone, A.J., and Wheeler, R.L., 2000, Data for Quaternary faults, liquefaction features, and possible tectonic features in the Central and Eastern United States, east of the rocky Mountain Front, UGSG OFR-00260, Prepared as part of the USGS NEHRP Map of Quaternary Faults and Folds.
Ellsworth, W.L., 2013, Injection-Induced Earthquakes, Science Vol. 341 no. 6142, http://www.sciencemag.org/content/341/6142/1225942
Freed, A.M., 2005, Earthquake Triggering by Static, Dynamic and Postseismic Stress Transfer: Annu. Rev. Earth Planet. Sci., 33, p. 335-367, doi:10.1146/annurev.earth.33.092203.12205
Gilbert, M. C. (1983a). The Meers Fault-Unusual Aspects and Possible Tectonic Consequences. Geological Society of America Abstracts with Programs, 18, 1.
Gilbert, M. C. (1983b). The Meers Fault of Southwestern Oklahoma-Evidence for Possible Strong Quaternary Seismicity in the Midcontinent [abs]. EOS, Transactions of the American Geophysical Union, 64, 313.
Gray, H. J., Mahan, S. A., Rittenour, T., Nelson, M. S., & Survey, U. S. G. (2014). GUIDE TO LUMINESCENCE DATING TECHNIQUES AND THEIR APPLICATION FOR Field
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Collection : Site Considerations. Harlton, B. H. (1951). Faults in Sedimentary Part of Wichita Mountains of Oklahoma. AAPG
Bulletin, 35(5), 988–999. Harlton, B.H., 1963, Frontal Wichita fault system of southwestern Oklahoma: American
Association of Petroleum Geologists Gulletin, v. 47, p. 1552-1580. Holland, A.A., 2013. Optimal Fault Orientations within Oklahoma, Seismol. Res. Lett., 84, 876-
890. Hornsby, K.T., 2017, Constraining the Holocene Extent of the Meers Fault, Oklahoma using
High-Resolution Topography and Paleoseismic Trenching, Portland State University, Masters Thesis, 123 pages. ISBN 9780355371857, https://search-proquest-com.proxy.lib.pdx.edu/docview/1988327059?pq-origsite=primo
Jones-Cecil, M., 1995, Structural controls of Holocene reactivation of the Meers fault, southwestern Oklahoma, from magnetic studies, GSA Bulletin, 107, p.98-112.
Kelson, K.I., and Swan, F.H., 1990, Paleoseismic history of the Meers fault, southwestern Oklahoma, and implications for evaluations of earthquake hazards in the Central and eastern United States, in Weiss, A.J., ed., Seventeenth water reactor safety information meeting: Proceedings of the U.S. Nuclear Regulatory Commission NUREG/CP-0105, v.2, p. 341-365.
King, G.C.P., Stein, R.S., and Lin J., 1994, Static Stress Changes and the Triggering of Earthquakes, Bulletin of the Seismological Society of America, Vol. 84, No. 3, pp. 935-953.
Lienkaemper, J.J., and Ramsey, C.B., 2009, OxCal: Versatile Tool for Developing Paleoearthquake Chronologies--A Primer: Seismological Research Letters, v. 80, p. 431–434, doi: 10.1785/gssrl.80.3.431.
Luza, K.V., Madole, R.F., and Crone, A.J., 1987, Investigation of the Meers fault in southwestern Oklahoma: Oklahoma Geological Survey Special Publication, Bulletin, v. 100, 75p.
Madole, R.F., 1988, Stratigraphic evidence of Holocene faulting in the mid-continent – The Meers fault, southwestern Oklahoma: Geological Society of America Bulletin, v. 100, p. 392-401.
Reimer, P. J., Bard, E., Baillie, M. G. L., Bayliss, A., Beck, J. W., Blackwell, P. G., Bronk Ramsey, C., Buck, C. E., Cheng, H., Edwards, R. L., Friedrich, M., Grootes, P. M., Guilderson, T. P., Haflidason, H., Hajdas, I., Hatté, C., Heaton, T. J., Hoffmann, D., Hogg, A. G., Hughen, K. A., Kaiser, K. F., Kromer, B., Manning, Niu, M., S. W., Reimer, R. W., Richards, D. A., Scott, E.M., Southon, J. R., Staff, R.A., Turney, C. S. M., and van der Plicht, J., 2013, IntCal13 and Marine13 radiocarbon age calibration curves, 0-50,000 years cal BP: Radiocarbon, v. 55, n. 4, p. 1869-1887.
7.0 PUBLICATIONS AND CONFERENCE PROCEEDINGS
Hornsby, K.T., 2017, Constraining the Holocene Extent of the Meers Fault, Oklahoma
using High-Resolution Topography and Paleoseismic Trenching, Portland State University, Masters Thesis, 123 pages. ISBN 9780355371857, https://search-proquest-com.proxy.lib.pdx.edu/docview/1988327059?pq-origsite=primo
Bennett, S.E.K., Streig, A., Hornsby, K. T., Chang, J.C., and Woelfel, I.E., 2016, EERI Clearinghouse of observational data from the 2016-09-03 Pawnee Oklahoma Earthquake. [GIS map] https://www.arcgis.com/home/item.html?id=6fc3fb778be041a688ff346ee0706c19
Hornsby, K.T., Streig, A., Bennett, S.E.K., Chang, J.C., 2017, Constraining the Holocene Extent of the Meers Fault, Oklahoma using High-Resolution Topography and
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Paleoseismic Trenching, SSA Annual Meeting, Denver, Colorado, April 17-21, 2017. (poster)
Hornsby, K.T., Streig, A., Bennett, S.E.K., Chang, J.C., 2017, Constraining the Holocene Extent of the Meers Fault, Oklahoma using High-Resolution Topography and Paleoseismic Trenching, AEG Oregon Chapter Meeting – Student Research Presentations, May 16, 2017. (poster)
Hornsby, K., Streig. A., Bennett, S., Chang, J., Woelfel, I., 2016, Constraining the Rupture Length and Timing of the Northwest Extension of the Meers Fault, Oklahoma using High Resolution Topographic and Age Data, Recent Advances in Tectonic Geomorphology, Dates, Rates, Models, and Beyond, AGU Fall Meeting, December 11-15, 2016, San Francisco, CA, EP11B-0994. (poster)
Bennett, S., Streig, A., Chang, J., Hornsby, K., Woelfel, I., Andrews, R., Briggs, R., McNamara, D., Williams, R., and D. Wald, 2016, Rapid Field Response to the 3 September 2016 M5.8 Earthquake Near Pawnee, Oklahoma: Summary of Structural Damage and Liquefaction Observations, Pawnee EQ Late-Breaking Session, AGU Fall Meeting, December 11-15, 2016, San Francisco, CA, S44C-01. (talk)