NGA-East: National Seismic Hazard Mapping Perspective

Mark Petersen

USGS

Golden, CO

New Madrid Ground Motions

• Tennessee: Lowered building codes• Arkansas: Legislative hearing to lower building

codes (Have these ground motions occurred historically?, How do they compare to California earthquake ground motions?)

• Kentucky: Ground motion equations are conservative, uncertainties high, PSHA not valid- mixing temporal

• Building code community: Can these ground motions occur? Are there physical limits that can be applied? Have we adequately accounted for the distribution of ground motions and truncation levels?

New Hazard Maps

Ratio of new hazard maps with 2002 maps

Figure 9: CEUS 0.2 s SA attenuation relations for M 7 earthquake on Vs30 760 m/s site conditions: AB95 AB05 (Atkinson and Boore, 1995, 2005; F96 (Frankel et al., 1996); T97 T02m (Toro, 1997, 2002); C03 (Campbell, 2003); S01 (Somerville 2001); SV02 (Silva et al., 2002); TP05 (TavakoliAnd Pezeshk, 2005) From Chris Cramer

Figure 10: CEUS 1 s SA attenuation relations for M 7 earthquake on Vs30 760 m/s site conditions: AB95 AB05 (Atkinson and Boore, 1995, 2005; F96 (Frankel et al., 1996); T97 T02m (Toro, 1997, 2002); C03 (Campbell, 2003); S01 (Somerville 2001); SV02 (Silva et al., 2002); TP05 (TavakoliAnd Pezeshk, 2005)

From Chris Cramer

FromAtkinson and Boore(2006; updated 2007)

Does this contradictIntensity data fromCEUS and WUS Earthquakes?

Differences

1. Geometrical spreading (r-1.3 vs r-1.0)2. Stress drop3. Site kappa (0.01 vs 0.02)

Amplitudes decay faster than 1/R at R<70 km. Amplitudes decay faster than 1/R at R<70 km. This has important implications for This has important implications for ENA ground motion relations.ENA ground motion relations.

From Gail Atkinson

Average Stress Drop Determinations

570 bars

290 bars

110 bars

≥410 bars

From Art Frankel

Some intriguing ground motion information from MMI, based on the USGS “Did You Feel It?” website database.Higher ENA MMI appears to persist to near-source, suggesting higher stress drops

Slide and caption from Gail Atkinson

From Art Frankel

From Frankel et al. (1990)

Conclusions

• Need more information on geometric spreading, stress drop, kappa

• Need to resolve the discrepancy between new attenuation relations and MMI data

• Need to determine whether high values over New Madrid are reasonable

• Need to involve CEUS ground motion modelers (Hermann, Chapman, Ebel, others)

Corrected for Atkinson Q model and B-C boundary site amplification

Acc

eler

atio

n S

pect

ral A

mp.

Frequency (Hz)

kappa= 0.01

kappa= 0.02

Vs30= 705 m/secVs30= 470 m/sec

We used kappa=0.01 for CEUS B-C sites

location dateMw

(From Herrmann)

MblgDepth

(km)

Corner Frequency

(hz)

Stress drop

(bars)

W. KY6/20/05

12:213.6 3.7 21 8-12 270-880

N.E. AR5/1/05

12:374.2 10 2-5 32-510

MO-AR border

10/21/99

8:183.7* 3.9 11 ≥ 8 ≥410

Fort Payne,

AL

4/27/03

8:594.6 4.9 12 2-3 130-440

S.W. Utah

2/23/01

21:434.2 10 2 32

S.W. Utah

10/22/99 19:06

4.0 6 3 55

Stress Drop Determinations from Spectral Ratios

* Determined from comparison of spectral levels with 5/1/05 event

From Art Frankel

USINVs30= 705 m/sec

OLILVs30= 470 m/sec

What is kappa (high-frequency spectral falloff) for CEUS B-C sites? Vs30= 760 m/sec

5/1/05 earthquake, NE Arkansas, M4.2, fc= 2 Hz (at OLIL)

Corrected for Atkinson Q model and B-C boundary site amplification

Acc

eler

atio

n sp

ectr

al A

mp.

Frequency (Hz)

USIN OLIL

PVMO

Mw= 3.6 (Herrmann), fc= 8-12 Hz, stress drop=270-880 bars

fc= 12 Hz fc= 12 Hz

fc= 9 Hz

8

UTMT

fc= 8 Hz

Western Kentucky 6/20/05 12:21 UTC, d= 21 km S

pect

ral R

atio

Spe

ctra

l Rat

io

Frequency (Hz) Frequency (Hz)

All spectral ratios wrt Md 2.7 foreshock

8

USIL

red: fc= 12 Hzblue: fc= 8 Hz

OLIL

red: fc= 12 Hzblue: fc= 8 Hz

uncorrected spectra (proportional to velocity 1-10 Hz)

6/20/05 W. Kentucky Station USINDist= 167 km

From Art Frankel

Brune spectra forearthquakes whose moments

differ by factor of 125 and have equal stress drops

Ratio of spectrum of larger eventdivided by spectrum of smaller event

fc= 5 Hz

fc= 25 Hz

fc= 5 Hz

fc= 25 Hz

Taking spectral ratio of collocated earthquakes removes path and site effects (and instrument response) and provides estimate of corner frequency of large event

(and the small event if you have sufficient bandwidth)

From Art Frankel

Red stars showearthquakes studied here, Mw 3.6-4.6

Triangles are broadband stationsof the New Madrid seismic network andother ANSS stations used inthis study

From Art Frankel