figure 4.1 hls histories of all sites, plotted with the aligned time
TRANSCRIPT
-40
-30
-20
-10
0
10
20
30
40
50
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
-2.2 +/-2.42 2 +/
1 2 +/-0 3
Bdg99A3
Bdg99A1
-40
-30
-20
-10
0
10
20
30
40
50
60
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
-2.9 +/-1.79 +/ 1 7
-9.0 +/-3.0
-9
3 0
-6.1 +/-0.70 7/ 0 7/ 0 7
Tb97
Tb00A1
Uneroded HLSEroded HLS
Tectonic rate/displacement
dashed where less certaindotted where extrapolated
(a) Bendera
(b) Badgugu West
4-68
Rel
ativ
e E
leva
tio
n o
f H
LS
(cm
)
Figure 4.1 HLS histories of all sites, plotted with the aligned time scale and the same
scaling of emergence and submergence relative to modern HLS. The 1935 event
dominates the history. The 1962 event is the second largest event. The vertical
deformation rates vary markedly from site to site and for different periods.
-15
-5
5
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
(g) Antinang(g) Antinang
(h) Memong, head A2
(i) Memong, head A1
-10
0
10
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Tf99B1Tf99Ct(f) Tofa
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
-0.3 +/-0.7
Pn00A1-east wingg
Pn00A1-west wing
Pn97P 97(e) Pono
-30
-20
-10
0
10
20
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
-2.0 +/-0.8
Brg00A1 Brg-97
(d) Barogang
-50
-40
-30
-20
-10
0
10
20
30
40
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
-5.1 +/-3.2
-9.3 +/-1.9
(c) Badgugu-East
Bdg00B1
4-69
Rel
ativ
e E
leva
tio
n o
f H
LS
(cm
)
Figure 4.1 Continued ...
-10
0
10
20
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Ba97B1 Ba97B2(l) Bai
-20
-10
0
10
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Pe97-1(k) Penang
-40
-30
-20
-10
0
10
1880 1890 1900 1 20 1930 1940 1950 1960 1970 1980 1990 2000
Taj00A1west-side cut
Taj00A1east side cut
(j) Tanjung Anjing
-20
0
10
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
9A1
0.8 +/-0.2(i) Memong Head 1
-20
-10
0
10
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Mm97A2
(h) Memong Head 2
4-70
Rel
ativ
e E
leva
tio
n o
f H
LS
(cm
)
Figure 4.1 Continued ...
-10
0
10
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Te97
(q) Telur
-20
-10
0
10
20
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
1
Sm97-1
Sm97-1
-10
0
10
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Lm99A1
-30
-20
-10
0
10
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Msn00A1
-40
0
10
20
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
2.0 +/-0.6/ 0 6-2.2+/-1.4
1.1 +/-0.21 1
Lg99A1g
-2.6 +/-1.0/ 1 0(m) Lago
(n) Masin
(o) Lambak
(p) Sambulaling
4-71
Rel
ativ
e E
leva
tio
n o
f H
LS
(cm
)
Figure 4.1 Continued ...
50km-Benioff isobath
99˚
00'E
98˚
00'E
98˚
30'E
0˚ 30'S
0˚
25km
Sumatra
Pini
Tanabala
Tanamasa
Siberut
Masin
1997(3-10)
1993-4(2.5/-6)
1994-eroded1994(>1.5)
1994(8.5)
1995(1.5)
1994(4-5)
1994(3)
1994(0.3/)
1994(>1.5/)
1994(1)
1993-4(3)
1994(7/)
1994-not affected1994-eroded?
1994(2)
1994-not affectedMemong
LagoLambak
Sambulaling
TelurAntinang
Pono
Barogang
Bendera
West BadguguEast Badgugu
Penang
Bai
1986(10)
1986(>2.5/-10)
1986(2.5/-5)
1986(>12/-12)
1986-7(2)
1987(0.5-3.5)
1986-not affected
1987(2)
1986-freegrowth
1986-eroded?1986-eroded?
1986-eroded?
1986-eroded?
1986-eroded?
1986-eroded?
1982(>1.5)1982(4)
1982(3)
1982(3)
1982(2.5)
1982-3(1.5)
1982-eroded?1982-not affected
1982-eroded?
Tofa
Tj.Anjing
Figure 4.2 Non-tectonic HLS die-downs during ENSO and IOD (Indian Ocean Dipole) events. Values in the brackets are measured emergence/submergence (-) from the paleogeodetic records.
4-72
(12/-12) = emergence/submergence (cm)
50km-Benioff isodepth
99˚
00'E
98˚
00'E
98˚
30'E
0˚ 30'S
0˚
25km
Sumatra
Pini
Tanabala
Tanamasa
Siberut
Masin 1991(4)
Lambak
1990(4)
Tofa
1958(4/-4)
1919.5(7/-8.5)
Bendera
1978-9(9/-12)
1976(5)
1979(2)
1974(2.5)
1974(2)
1978(4.5)
1991(1)
1991(1)
Pono
1986(10)
Figure 4.3 HLS die-downs that occurred locally. At the Pono site, the die-down in 1986 was probably of tectonic origin. The emergence/submergence episodes of 1978-9 at Bendera may reflect a very local tectonic event. At Masin and Lambak the die-down of ~1990 was possibly related to an earthquake event (Mw 5.2), but it may also be influenced by cyanide fishing. Sites with black letters probably experienced non-tectonic die-downs.
Lago
1994(7)
Bai
Sambulaling
4-73
-6
-3
0
3
6
1965 1970 1975 1980 1985 1990 1995 2000
-6
-3
0
3
6
-6
-3
0
3
6
Figure 4.4b Angsa site. During our visit in mid-1997, numerous living microatolls showed pristine micro-topography on their upper surface, characterized by alternating concentric ridges and swales.
HL
S re
sidu
al (
cm)
Bai
Sambulaling
Angsa
Figure 4.4a Three sites with particularly good HLS records allow calculation of uncertainties in rates of submergence/emergence due to annual fluctuations in lowest low tides. These three residual plots of the HLS records show the HLS fluctuations. The 2σ standard deviations are +/- 2.6 cm at Bai, +/-2.7cm at Sambulaling, and +/-2.8 cm at Angsa. The average HLS uncertainty is +/- 2.7 cm. This is the uncertainty that we can assign assign then to uneroded HLS records. Bai and Sambulaling data are from Fig. 3.42 and 3.50 respectively.
4-74
0
0
cm
191
19
Stage3: 3cm erosion at crests
970770
1975975
191965
Stage2: 2cm erosion at crests
0
1980
11995995
1990
1975751975
1965
Stage1: 1cm erosion at crests
Stage4: 4cm erosion at crests
?
Sm97- actual head cross section in 1997
Figure 4.5 Erosions adds additional uncertainty to the rate calculations. These five figures
show a hyphothetical degradation of a coral surface assuming erosion occurs predominantly as a diffusive process. The ridges erode more rapidly than swales, because of their more exposed position and greater ratio of surface area to volume.
4-75
-10
0
5
10
15
-10
-5
10
15
-10
5
10
15
-10
5
10
15
-10
-5
0
5
15
Ele
vatio
n of
HLS
rel
ativ
e to
cre
st o
f liv
ing
ring
(cm
)
Actual HLS history from Sm97-1
1cm erosion of the coral surface
2cm erosion of the coral surface
3cm erosion of the coral surface
4cm erosion of the coral surface
1.9 +/- 0.5 mm/y1 9 /
(a)
(b)
(c)
(d)
(e)
Figure 4.6 Graphical representations of coral degradations shown in the previous figure. The
standard errors of the averaged vertical motion rates are calculated using the weighted-least-
squared method described in the text. The assigned uncertainties of the 2-σ HLS records are
proportional to the severity of erosion.
2.3 +/- 0.7 mm/y2 3 +/ 0
2.3 +/- 1.1 mm/y2 3 +/ 1
4-76
Pini Basin
99˚
00'E
50km
-Wadati B
enio
ff Zone is
obath
98˚
00'E
98˚
30'E
0˚ 30'S
25km
Equator
-600
-1200
-600
-600
-240090
50
30
10
-10
Lago(-34+/-4)
Tj. Anjing(-28+/-5)
Memong(-8+/-5)
Pono(-10+/-6)
Masin(-19+/-4)
Sambulaling(-11+/-4)
-30-10
Labuan Bajau(~ -7 )
East Badgugu(+67+/-13)
Bendera(90+/-8)
Barogang(+35+/-8)
70
Figure 4.7 Vertical displacements during the 1935 event. The values of emergence (red) and submergence (green) are in cm and are plotted with their 2-σ uncertainty. The red and green lines are contours of the values. Contours of bathymetry (blue) are in meters. The 25-km isobath of the subduction interface cuts diagonaly accross the map.
4-77
1
2
3
4
5
6
7
8
1920 1925 1930 1935 1940 1945
Tb00A1
Bdg00B1
Brg00A1
Pn00A1
Mm00A1
Lg99/00A1
Taj00A1
Msn00A1
Figure 4.8 Date ranges of the December 1935 event based on visual ring counting from the
exterior ring. The weighted average of the dates is 1935.8 +/-0.6 (2σ).
-40 -30 -20 -10 0 10 20 30 40 50
Tb00A1-3aBdg00B1-2bBdg00B1-3aBdg00B1-4bBrg00A1-2aBrg00A1 2aBrg00A1-3aBrg00A1-4aPn00A3-2b-1Pn00A3-2b-2Pn00A3-4bPn00A3 4bPn00A3-5bMm00A1-3aLg00A1-1bLg00A1-2aTaj00A1-2aTaj00A1 2aTaj00A1-3aTaj00A1-4aTaj00A1-4bTaj00A1-5b
Tf99C1At99A1-2Lm99A1-1a
Age differences (years)
Figure 4.9 Date ranges for the 1935 event, based upon U-Th dates (red squares) and their 2σ
uncertainties (red bars) compared to the assigned ages from the visual ring counting (bold gray
line with gray bars).
4-78
99˚
00'E
50 k
m W
adati-B
enio
ff Zone Is
obath
98˚
00'E
98˚
30'E
0˚ 30'S
Equator
-25 k
m
20
402060
-20
-10
Lago(-34+/-4)
Tj. Anjing(-28+/-5)
Memong(-8+/-5)
Pono(-10+/-6)
Masin(-19+/-4)
Sambulaling(-11+/-4)
-10
Labuan bajau (~ -7)
East Badgugu(+67+/-13)
Bendera(90+/-8)
Barogang(+35+/-8)
Figure 4.10 A comparison of vertical deformations for the 1935 event. Values plotted under site names are from analysis of our microatoll records. Contours are from elastic dislocation model derived from seismologic rupture parameters, and the yellow rectangle is the seismologically determined source in plan view from Rivera et al. [2002].
4-79
99˚
00'E
50 k
m-W
adati-B
enio
ff zone is
obath
98˚
00'E
98˚
30'E
0˚ 30'S
25 k
m
Equator
-14+/-4
-5+/-6
2+/-5-4+/-4 ~ -5+/-4
15+/-920+/-8
15+/-8
Figure 4.11 Difference between measured uplift determined from microatolls and the uplift predicted by the elastic dislocation model. In general, the measured values of both emergence and submergence are greater than the predicted values. This may mean that significant aseismic afterslip occurred soon after the earthquake.
2 +/-5
4-80
100 0 100 200 300 400
Distance (km)
Upl
ift (
cm)
Dep
th (
km)
0
40
80
120
160
88.0(14.8)
125.0 (27.0)
Slip=2.33 meters
1935 EventBrg
Figure 4.12 2-D fit to microatoll data for the 1935 event. In Panel A the data are projected
onto a cross section perpendicular to the trench axis. In Panel B the data are projected onto a
cross section drawn 10 degree counter-clockwise from the line perpendicular to the trench axis.
Black numbers with arrows are the distance from the trench and the depth to the Wadati-
Benioff zone (in kilometers) of the updip and downdip limits of the 1935 rupture patch.
Panel B
100 0 100 200 300 400 500
Distance (km)
Upl
ift (
cm)
Dep
th (
km)
0
40
80
120
160
94.0(16.8)
125.0 (27.0)
Slip=2.52 meters
1935 EventBrg
Panel A
4-81
1950 1955 1960 1965 1970
Figure 4.13 Date ranges for the 1962 event based on visual ring counting.
Tb00A1Tb00A1
Bdg00B1Bdg00B1
Brg97Brg97Brg00A1Brg00A1
Pn97Pn97Pn00A3Pn00A3
Lg99A1Lg99A1
Taj00A1Taj00A1Msn00A1Msn00A1
Tf99C1Tf99C1
Pe97Pe97
Ba97B1Ba97B1
Lm99A1Lm99A1
Sm97-1Sm97 1
4-82
Pini Basin
99˚
00'E5
0km
98˚
00'E
98˚
30'E
0˚ 30'S25km
Equator
7+/-4
6+/-4
2+/-4
4+/-4
0+/-4
7+/-6
7+/-5
7+/-4
1+/-5
0+/-4 0+/-4
13+/-4
9+/-5 2+/-4
5+/-5
10
1010 cm
55
5
0
Figure 4.14 Map of emergence event that occurred in 1962. Values are in centimeters. Though coverage is incomplete the contours of uplift suggest two NE-trending ridges of emergence. Yellow shaded patches with dashed boundaries suggest which section of the subduction interface might have slipped to produce the pattern of uplift. Arrows indicate directions of slips.
4-83
Pini Basin
99˚
00'E
50km
98˚
00'E
98˚
30'E
0˚ 30'S
25km
Equator
-10-20
-10
-20
-20
-5
-10
?
-9+/-4
-8+/-4
-23+/-7
-21+/-6
-11+/-4
-14+/-5
-9+/-4-4+/-4
-11+/-4
-7+/-4
-2+/-4
-16+/-6
-8+/-4-12+/-6
Figure 4.15 Submergence that occurred in 1962 (values in centimeters). The pattern of the submergence, as delineated by the red contours, suggests slip on those patches of the subduction interface that did not slip in the preceding emergence event.
4-84
0 81624
0 100 200 300 400
Upl
ift (
cm)
Dep
th (
km) 40
80
120
160117.2(24.2)-133.2 (30.3)
Slip=1.66 meters
1962 Submergence
Slip=1.15 meters
103.0(19.3)
0
10
20 0 100 200 300 400
40
80
120
160
Distance (km)
Upl
ift (
cm)
Dep
th (
km)
1962 Emergence
1m slip
Figure 4.17 Data of the 1962
submergence are predicted by
slips on the outboard patch of
the 1935 rupture and on the
narrow patch near the down-
dip edge of the 1935 slip
source. Scattering of the data
may suggest slip variations
along the strike. Uniform slips
of 1.7 m on the orange patch
and 1.2 m on the red patch
produce the double-troughed
deformation pattern shown in
green. The model curve fits
much of the data, but the two
extreme submergence values
are grossly underfitted.
Figure 4.18 Superposition of the slips on the subduction interface from the 2-D elastic
dislocation models of 4.16 and 4.17. The 1962 slip patches overlap with the 1935 rupture but
extend farther up-dip and down-dip. This may indicate that the 1962 silent event facilitates the
distribution of slips throughout the broader interface.
Figure 4.16 The 2-D elastic dislocation fit of the paleogeodetic data of the 1962 emergence
event. Slips are allowed to vary along the patch. The observed emergences are explained by
slips on and near the lower boundary of the 1935 patch and on a wider patch further down-dip.
Black dots and vertical bars represent values of paleoseismic emergence with their 2-σ errors.
The scatter of the data reflects their variability along strike. Red bars indicate the sections of the
subduction interface that slipped. Bold orange lines show the magnitude of slips on the
subduction interface prescribed by the inversion. The triangular shape of the orange line
indicates that we have allowed slip to vary on the interface. The thin red curve is the modeled
vertical surface deformation.
0 81624
0 100 200 300 400
40
80
120
160
1962 Emergenceand Submergence
1935 rupture
1.2m0.5m
1.0m
1.7m1.7m
4-85
-10
1890 1900 1910 1920 1930 1940 1950 1960 1970
10
1.6 +/-1 7
Figure 4.19 Paleogeodetic records derived from HLS records, but corrected for a 2 mm/yr
global glacio-hydro-isostatic sea-level rise.
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
-10
10
20
3.9 +/-1.09 +/
Sambulaling
Telur
20
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
0
Lambak
20
1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
-20
-10
0
1.3 +/-0.91.5 +/-1.81 5 +/ 1 8
Masin
30
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
-30
-20
-10
10
20
4.0 +/-0.64 0
-4.3+/-6.3
-0.2+/-1.44
3.1 +/-0.23 4.6 +/-1.0
+/-1
30
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
0
20
BaiR
elat
ive
Ele
vatio
n (c
m)
Lago
20
1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
10
5.8+/-1.4+/-1Penangg
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
-30
-10
0
100.1 +/-2.8 ?
6.1 +/-2.46 1
Tj.Anjing
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
-10
1 +/-2 ?? 2.5 +/-0.6
20
980 1990 2000
-
0
2.5 +/-0.62
Memong-head 2
1930 1940 1950 1960 1970 1980 1990 2000
1.3 +/-0.4
Rel
ativ
e el
evat
ion
(cm
)
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1990 2000
0
10-1.5 +/-0.61.5 +/-0 6
Tofa
30
1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
-10
0
10
201.7 +/-1.4+/ 1 41.7 +/-0.70.70.9 +/-0.5
5+/-25+
Pono
1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
-10
0
20
-20
-3.0 +/-0.8-3 0 +/ -0.4 +/-0.6
Barogang
-10
0
10
20
30
1920 1930 1940 1950 1960 1970 1980 1990 2000
40
-7.3 +/-1.9
7.9
-3.1 +/-3.23 1 +/
East Badgugu
-40
-30
-10
0
10
30
40
1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
-2.3 +/-3.62 31.6 +/-0.80.8
-0.2 +/-2.40.2West Badgugu
-0.9 +/-1.7
-7.0 +/-3.0
-1.2 +/-1.3 -7.9 +/-4.5
-4.1 +/-0.7-10+/-2.4
0 +
0.9
10+
/ 1 3 -7.9/ 1 3 -7.9
-20
0
10
20
30
40
50
9 +/ 4
1930 1940 1950 1960 1970 1980 1990 2000
70
Tj.Bendera
WEST
EAST
a
bb
c
ddd
e
ffff
ggg
hh
iii
jjjj
lll
m
n
o
pp
qqqqqq
4-86
Pini Basin
99˚
00'E
50km
-Benio
ff isobath
98˚
00'E
98˚
30'E
0˚ 30'S
25km
-Benio
ff isobath
Equator
Tanabala
Tanamasa
Pini
1
-40
32
-4.1+/-0.7
Badgugu0.8+/-0.3
Barogang0.0+/-0.8
Pono0.9+/-0.5
Memong2.8+/-0.2
3.1+/-0.2
Bendera
Lago
Figure 4.20 Rates of slow vertical deformation prior to 1935, adjusted for 2 mm/y of the global sea level rise. Shaded domain is the region that was slowly submerging. The highest recorded submergence was ~4 mm/yr. Eastern part of the islands was emerging. The highest emergence was ~3 mm/yr
4-87
Pini Basin
99˚
00'E
50 k
m W
adati-B
enio
f zone is
obath
98˚
00'E
98˚
30'E
0˚ 30'S
25km
Equator
-3
2
0
2 1
Bendera-7+/-3 East Badgugu
-7.3+/-1.9
Barogang-3.0+/-0.8
Pono1.7+/-0.7
Masin1.5+/-1.8
Figure 4.21 Average rates (mm/y) of post-seismic deformation from 1935 to 1961 after a rate adjustment by 2 mm/yr for global sea-level rise (data from Fig.4.19). Submergence rates of the sites in the western part abruptly increased. The highest recorded submergence is 7 mm/yr.
Tanabala
Tanamasa
Pini
4-88
Locked patch?
Pini Basin
99˚
00'E
50km
-Benio
ff isobath
98˚
00'E
98˚
30'E
0˚ 30'S
25km
0
23
45
6
-1
-2
21
234
?
?
?
-0.9+/-1.7
-0.2+/-2.4-3.1+/-3.2
-0.4+/-0.6
1.7+/-1.4
1.5+/-0.6
1.3+/-0.4
2.5+/-0.6
6.1+/-2.4
5.8+/-1.4
6.0+/-1.1
4.6+/-11.3+/-0.9
3.2+/-0.8
3.9+/-1.0
1.6+/-1.7
Equator
?
TanabalaIsland
TanamasaIsland
Pini Island
Figure 4.22 Modern rates (1962-2000) after 2 mm/yr adjustments for the global sea-level rise. Values are in milimeters per year. Contouring of the values shows that the hingeline runs parallel to the trench. The maximum submergence occurs around the southwestern part of Tanabala Island. The larger maximum emergence is centered about 10 km off the east coast of Tanamasa Island. An "odd" ridge of emergence runs almost parallel to the long axis of Pini Island.
4-89
top interface
bottom interface
Coseismic
interseismic
A
B
C
D
Vplate
Vplate
Vplate
Vout
Mantle
Slab
Overriding Plate
d lock dslipT
trench
Figure 4.23a Sketch showing the parameters of an idealized elastic dislocation model of interseismic deformation at a subduction zone [after Sieh et al., 1999]
Figure 4.23b An elastic dislocation model of an earthquake cycle. Red patches slip equal to a plate rate (i.e. a fraction of aseismic slip is 1.0) during an interseismic period. Panels A and B show contributions to vertical motion from indivdual sources. Panel D shows a total vertical motions. Note that motions due to the top and the bottom interfaces are nearly mirror image to each other. So, in a steady state subduction they nearly cancel one another. Panel C shows vertical motion in a seismic event, which is nearly a mirror image to that of the interseismic period [from Steve Ward, written comm., 2002].
4-90
a fraction of plate rate
Figure 4.24 Elastic dislocation models of slow vertical deformation prior to 1935.
Panel A uses a 2 mm/y global sea level rise correction. Panel B assumes 1 mm/y. The
high rate of submergence and low rates of emergence require rates of slip on the
subjacent interface that are 50 -75% of the long-term plate rate. Slip rates on the
interface between the islands and the trench are appreciably higher than the long-term
plate rate.
0 2 4 6
0 100 200 300 400Distance (km)
Upl
ift (
mm
/y)
Dep
th (
km) 40
80
120
160125.0 km
Panel APre 1935
Slip=55 mm/y
Slip=40 mm/yBaseline= 2 mm/y
Slip=25 mm/y
83.5
Xout
Xslip
MmLg
Tb
0 2 4 6
0 100 200 300 400Distance (km)
Upl
ift (
mm
/y)
Dep
th (
km) 40
80
120
160125.0 km
Panel BPre 1935
Slip=72 mm/y
Slip=40 mm/yBaseline= 1 mm/y
Slip=30 mm/y
83.5
4-91
Figure 4.25 Elastic
dislocations modeling of
slow vertical deformation
for the period from 1935
to 1961. Paleogeodetic
data are projected onto a
cross-section
perpendicular to the
trench. Both Panel A and
B have a fixed boundary
at 125km from the trench
but use a global sea-level
rise correction of 2 mm/yr
and 1 mm/yr respectively.
In Panel C this boundary
has been allowed to
move. In all three models
the up-dip section slips at
or slightly faster than
long-term plate rate. Data
from the western part
require the 1935 rupture
patch to creep at about a
quarter of the long-term
plate rate. Panel C shows
that intrusions of the
creeping up-dip and
down-dip sections into
the healed 1935 rupture
patch better fit the eastern
data.
0 2 4 6
0 100 200 300 400U
plift
(m
m/y
)D
epth
(km
) 40
80
120
160
Distance (km)
95.3(16.9)
125 (27)
Slip=40 mm/y
1935-1961
Slip=41 mm/y
Baseline= 2 mm/y
Slip= 9 mm/y
Panel A
Msn
0 2 4 6
0 100 200 300 400
Upl
ift (
mm
/y)
Dep
th (
km) 40
80
120
160
Slip=40 mm/y
1935-1961
Slip=53 mm/y
Baseline= 2 mm/y
Slip=9 mm/y
115.7(23.6)100.4(18.5)
Panel C
0 2 4 6
0 100 200 300 400
40
80
120
160
Upl
ift (
mm
/y)
Dep
th (
km)
95.3(16.9) 125
(27)
Slip=40 mm/y
1935-1961
Slip=54 mm/y
Baseline= 1 mm/y
Slip=14 mm/y
Panel B
Mm
4-92
112.8(22.8) 125(27)
Slip=40mm/y
Slip=27 mm/y
Baseline= 2 mm/y
Slip=9 mm/y
Panel B1962-2000
135(31)
Slip=40 mm/y
Slip=0.0 mm/y
Baseline= 2 mm/y
Slip=0.0 mm/y
Panel A1962-2000
0 2 4 6
0 100 200 300 400
40
80
120
160
Upl
ift (
mm
/y)
Dep
th (
km)
108.5(21.1) 125 (27)
Slip=40 mm/y
Slip=37 mm/y
Baseline= 1 mm/y
Slip=17 mm/y
Panel C1962-2000
0 2 4 6
0 100 200 300 400Distance (km)
Upl
ift (
mm
/y)
Dep
th (
km) 40
80
120
160
0 2 4 6
0 100 200 300 400
Upl
ift (
mm
/y)
Dep
th (
km) 40
80
120
160
Figure 4.26 The 2-D inverse elastic dislocation models of the modern rates (1962-2000). The
fully locked model in Panel A is an acceptable inverse model, but greatly under predicts the
important westernmost point. Models in Panel B and C fit the westernmost point and thus are
preferred solutions. The principal observation is that the submergence rates in the western part
have declined significantly since 1962. This requires that slip rates on the interface between the
island and the trench have decelerated to only about 65% of the long-term plate rate, but that the
zone of slippage extent farther down-dip onto the principal locked patch.
4-93
99˚
00'E
50km-B
enioff isobath
98˚
00'E
0˚ 30'S
25km
Equator
0
23
45
6
-1
-2
21
2
34
?
?
?
99˚
00'E
50km
98˚
00'E
0˚ 30'S
25km
Equator
-10
-20
-10
-20
-20
-5
-10
99˚
00'E
50km
98˚
00'E
0˚ 30'S
25km
Equator
10
1010 cm
55
5
0
7+/-4
6+/-4
2+/-4
4+/-4
0+/-4
7+/-6
7+/-5
7+/-4
1+/-5
0+/-40+/-4
13+/-4
9+/-5
2+/-4
5+/-5
Pini Basin
99˚
00'E
50 km W
adati-Beniof zone isobath
98˚
00'E
0˚ 30'S
25km
Equator
-3
2
0
2 1
-7+/-3-7.3+/-1.9
-3.0+/-0.8
1.7+/-0.7
1.5+/-1.8
99˚
00'E
50 km W
adati-Benioff Z
one Isobath
98˚
00'E
0˚ 30'S
Equator
-25 km
9050
30
10
-10
(+67+/-13)
(90+/-8)
(+35+/-8)
(-34+/-4)
(-28+/-5)
(-8+/-5)
(-10+/-6)
(-19+/-4)
(-11+/-4)
-10
-30
99˚
00'E
50km-B
enioff isobath
98˚
00'E
0˚ 30'S
25km
Equator
1
-40
32
-4.1+/-0.7
0.8+/-0.3
0.0+/-0.8
0.9+/-0.5
2.8+/-0.2
3.1+/-0.2
Tanabala
Tanamasa
Pini
-9+/-4
-8+/-4
-23+/-7
-21+/-6
-11+/-4
-14+/-5
-9+/-4-4+/-4
-11+/-4
-7+/-4
-2+/-4
-16+/-6
-8+/-4 -12+/-6
-0.9+/-1.7
-0.2+/-2.4-3.1+/-3.2
-0.4+/-0.6
1.7+/-1.4
1.5+/-0.6
1.3+/-0.4
2.5+/-0.6
6.1+/-2.4
5.8+/-1.4
6.0+/-1.1
4.6+/-11.3+/-0.9
3.2+/-0.8
3.9+/-1.0
1.6+/-1.7
(a) Deformation rates 1900-1935 (mm/yr)
(b) Vertical deformation of the1935 event (cm)
(c) Deformation rates 1935 - 1962 (mm/yr)
(d) Emergence event in 1962 (cm)
(e) Submergence event in 1962 (cm)
(f) Deformation rates 1962 - 2000 (mm/yr)
4-94
Figure 4.27 Summary of paleogeodetic records of vertical deformations for the 20th century.
Note that deformation rates differ significantly between the three periods separated by the 1935
and 1962 events. Submergence rates are fastest in the post-earthquake period 1935-1962. In the
past four decades the rates slowed down. These differences indicate changes in the the slip rates
and other processes operating on and around the subduction interface.
100
0
100
200
300
400
Uplift (cm) Depth (km) 0
40
80
120
160
88.0
(14.
8)12
5.0
(27.
0)
S
lip =
2.3
met
ers
Pan
el B
1935
Eve
nt
0 2 4 6
0 1
00 2
00 3
00 4
00D
ista
nce
(km
)
Uplift (mm/y) Depth (km) 4
0
80
120
160
Pan
el A
Pre
193
5
S
lip=5
.5 c
m/y
S
lip=4
cm
/yB
asel
ine=
2 m
m/y
S
lip=2
.5 c
m/y
Xou
t
Xsl
ip
83.5
(1
3.6)
125.
0 (2
7.0)
0 2 4 6
0 1
00 2
00 3
00 4
00
Uplift (mm/y) Depth (km) 40 8
0
120
160
S
lip=4
cm
/y
Pan
el C
1935
-196
1
S
lip=5
.3 c
m/y
Bas
elin
e= 2
mm
/y
S
lip=0
.0 c
m/y
115.
7(23
.6)
100.
4(1
8.5)
112.
8(22
.6)
125.
0 (2
7.0)
S
lip=4
cm
/y
S
lip=2
.7 c
m/y
Bas
elin
e= 2
mm
/y
S
lip=0
.9 c
m/y
Pan
el F
1962
-200
0 0 2 4 6
0
100
200
300
400
Uplift (mm/y) Depth (km) 4
0
80
120
160 01020
0
100
200
300
400
40
80
120
160
Dis
tanc
e (k
m)
Uplift (cm) Depth (km)
Pan
el D
1962
Em
erge
nce
1m s
lip
0 81624
0 1
00 2
00 3
00 4
00
Uplift (cm) Depth (km) 40
80
120
160
117.
2(24
.2)
Slip
=1.
66 m
eter
s
Pan
el E
1962
Sub
mer
genc
e
S
lip=
1.15
met
ers
103.
0(1
9.3)
133.
2 (3
0.3)
105.
0 (2
0.0)
127.
0 (2
8.2) 16
2-18
0 (4
0-50
)
Fig
ure
4.2
8 S
um
mar
y o
f th
e el
asti
c dis
loca
tion m
odel
s of
the
centu
ry-l
ong p
aleo
geo
det
ic h
isto
ry. T
he
1935 a
nd t
he
1962 a
re
the
maj
or
tect
onic
even
ts, an
d d
emar
cate
appre
ciab
le c
han
ges
in t
he
beh
avio
rs o
f th
e su
bdu
ctio
n i
nte
rfac
e.
4-95
0
100
200
300
400
500
600
700
800
0 20 40 60 80 100 120 140 160 180 200 220
1962-2000
1962-2000
1962 Submergence
19621962
EmergenceEmergence
1935-1961
1935-19611900-1935
up-dip
1935
rupture
down-dip stable sliding
Distance from trench axis (km)
EastWestC
um
ula
tive s
lip o
n the inte
rface (
cm
)
Figure 4.29 Seismic and aseismic slip history on the subduction interface from 1900 to 2000 based on paleogeodetic data and elastic dislocation models. The red, yellow, and green areas represent the amount of slips in the 1935, 1962 emergence, and 1962 submergence events respectively. All other colors represent aseismic slips during intervening periods. Stable sliding at plate rate is indicated as 100% on the right-side scale.
50
100
150
200
% o
f pla
te ra
te a
ccom
odate
d
ste
ady s
ubm
erg
ence
recentslip deficit
4-96
Equator
1S
2S
99E98E
-200
-200
-600
-1200
-600
-600
-600-1800
-2400-3000
-3600-4000
-4600
-5000
-200
I FZ
PLATE
VECTOR
60 m
m/y
r
No
rth
110
40
Trench
0
60 m
m/y
r(P
late
vecto
r)
7 mm/yr
WFSR
35
IFZ
axis
IFZ
70 km
5 M
a10 M
a
Pre
sent
Projection of
IFZ on the interface
Figure 4.30. Hyphothesis of the eastward moving of the subducting Investigator Fracture Ridge
zone (IFZ) along the Sumatran subduction. WFSR is Wharton Fossil Spreading Ridge zone. The
plate vector is ~7 degree eastward from the axis of the IFZ. Thus, the IFZ moves toward east
about 7 mm/yr. The IFZ moved about 70 km since 10 Ma or about 155 km along the trench axis.
This subducting IFZ may have led to the intense faulting on the hanging wall above and to the
high percentage of aseismic slip on the subduction interface. Gray shaded and yellow shaded
regions indicate the trails of and an approximate present position of the IFZ.
4-97