Possibility on Forecasting Aftershock Distribution from
Stress Change: Case Study for Inland Taiwan Earthquakes
Chung-Han Chan and Kuo-Fong Ma
（詹忠翰、馬國鳳）
Institute of Geophysics, National Central University
ABSTRACT
Large earthquakes yield casualty in life and damages in buildings. Unfortunately,
large subsequent aftershocks sometimes yield secondary disaster following the
mainshock. A possibility of estimating possible aftershocks distribution might be able
to help reducing the secondary disaster it might bring. Several studies (Parsons et al.,
2000; Lin and Stein, 2004; Stein, 2000) have discussed the Coulomb stress transfer
after earthquakes. The results show that the seismicity has significant correspondence
to the Coulomb stress change of the mainshock. The aftershocks usually located in
the region where the Coulomb stress change was increased in the mainshock. These
studies bring the possibility on predicting possible aftershock distribution from the
stress transfer. Furthermore, if the stress transfer can be done soon after the
mainshock, the forecasting of the possible aftershock distribution might be able to
reduce the secondary earthquake hazard from large aftershocks.
For this study, we first considered five earthquake sequences in this study,
namely 15th December 1993 Da-Pu (ML =5.7); 5th June 1994 Nan-Ao (ML =6.2); 17th
July 1998 Ruey-Li (ML =6.2); 22nd October 1999 Chia-Yi (ML =6.4); and 22nd
October 1999 Chia-Yi-2 (ML =6.0) earthquakes as shown in Figure1. Table1 shows
their source parameters (origin time, location of hypocenters, and local magnitudes)
determined by Central Weather Bureau Seismological Network (CWBSN). The
models of spatial slip dislocations determined by waveform inversion using Taiwan
Strong Motion Network (TSMN) data by Wu and Ma (2001), that we call the models
thus obtained as heterogeneous slip models, are introduced to calculate the
conditions of stress transfer shown as Figure2 which shows that no matter if the
mainshock and aftershocks are on the same rupture plans and the same types of faults,
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most of the aftershocks locate at the area where stress was increased. Furthermore,
we calculated the changes of Coulomb stress by a single fault according to the
rupture length, width, and displacement by magnitude of the earthquakes and
geometry of rupture planes by the scaling law (Ma and Wu, 2001) and the focal
mechanisms to compare with the distribution of the aftershocks (Figure3). Similar
results with those by heterogeneous models, most of the aftershocks locate at the area
where stress was increased. The comparison between this result with the results by
heterogeneous models indicates that the amounts of the aftershocks which located at
the area where stress are increased reduce which may result from the simplified
one-segment model for Da-Pu and Ruey-Li sequences. For Nan-Ao and Chia-Yi
sequences, By contrast, these amounts rise which may be attributed to the moment
magnitude over-determined and the larger scales of stress change attribute to the
homogeneous displacement on the whole rupture plane instead of the dislocation
centralization (asperity) by waveform inversions. For the 1999 Chi-Chi earthquake,
although the patterns of stress changes for the three stages as detail slip distribution
models, three-segments homogenous fault model, and one-segment homogenous
fault model, are slightly different from each other (Figure4), most prominent features
of the aftershock distribution can be explained by all three fault models, namely the
region near the Chia-Yi earthquake, and southern linear extension of the aftershock
near southern end of the Chelungpu fault.
On the basis of the rapid stress change calculation, it is also possible to have
stress change calculation using a homogenous fault model according to derived
scaling law of Ma and Wu (2001). Thus, once the location, magnitude and focal
mechanism of the earthquake are available, the stress change calculation can be
carried out to provide information on the possible aftershock distribution. The
calculation can be further updated accordingly to the detail slip distribution
determination through the time to provide more precise information to the
distribution of aftershocks.
REFERENCES
Lin, J. and R.S. Stein (2004) Stress triggering in thrust and subduction earthquakes,
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and stress interaction between the southern San Andreas and nearby thrust
and
strike-slip
faults,
J.
Geophys.
Res.,
109,
B02303,
doi:10.1029/2003JB002607.
Ma, K.- F. and S.- I. Wu (2001) Quick slip distribution determination of moderate to
large inland earthquakes using near-source strong motion waveforms,
Earthquake Engineering and Earthquake Seismology, 3, 1-10.
Parsons, T. (2002) Global observation of Omori-law decay in the rate of triggered
earthquakes: Large aftershocks outside the classical aftershock zone, J.
Geophys. Res., 107, 2199, doi:10.1029/2001JB0006462.
Stein, R. S. (1999) The role of stress transfer in earthquake occurrence, Nature, 402,
605-609.
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Earthquake
Ruey-Li
1998
Chia-Yi
1999
Chia-Yi-2
1999
6
7
10
10
5
17
22
22
21
1
4
2
3
minute
49
9
51
18
10
second
43.1
30.09
14.96
556.8
17.5
Longitude (°)
120.523
121.838
120.663
120.422
120.431
Latitude (°)
23.213
24.462
23.503
23.517
23.533
12.5
5.3
2.8
16.59
16.74
5.7
6.2
6.2
6.4
6
strike (°)
200
87
45
180
45
Focal Mechanism
dip (°)
48
81
50
42
90
rake (°)
84
8
110
56
0
Moment
Magnitude (Mw)
Wu and Ma, 2000
5.66
6.28
5.85
6.16
5.87
5.99
Origin Time
Location
year
Da-Pu
1993
Nan-Ao
1994
month
12
day
15
hour
depth (km)
Magnitude (ML)
Fault Length (km)
Fault Width (km)
Fault Area (km2)
Displacement (m)
One segment
5.7
6.19
6.19
6.34
Wu and Ma, 2000
9
15
10
8
5
One segment
4.62
10.97
10.97
15.49
7.76
Wu and Ma, 2000
7
13
8
7
4.5
6.24
One segment
4.55
7.7
7.7
9.51
Wu and Ma, 2000
63
195
80
56
22.5
One segment
21.05
84.49
84.49
147.33
48.46
Wu and Ma, 2000
0.259
0.567
0.307
1.27
1.17
One segment
0.234
0.436
0.436
0.559
0.34
Table2 The source parameters and fault plane parameters of the events investigated
in this study.
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Figure1 The circles represent the distribution of the earthquakes with ML > 5.0 since
1993 in Taiwan area. The Stars denote the events with high aftershock activity
that can be investigated the relation between stress transfer and seismicity
changes after earthquake.
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Figure2 The Coulomb stress changes by the models of spatial slip dislocations
determined by heterogeneous slip models for comparison with one-month
aftershocks (dot). Due to the variation of stress changes at depths for the thrust
type earthquakes, stress changes associated with the Da-Pu, Ruey-Li and
Chia-Yi earthquakes with aftershock seismicity within 3 km of each profile are
shown at different depths. Because of less than one hour occurrence in time for
the two Chia-Yi earthquakes, the Coulomb stress changes of these two events
are considered simultaneously to represent the final Coulomb stress change
after the 22nd October, 1999.
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Figure3 The Coulomb stress changes by a single fault according to the rupture length,
width, and displacement by magnitude of the earthquakes and geometry of
rupture planes by the scaling law (Ma and Wu, 2001) and the focal mechanisms
for comparison with the distribution of the aftershocks (dot). Due to the
variation of stress changes at depths for the thrust type earthquakes, stress
changes associated with the Da-Pu, Ruey-Li and Chia-Yi earthquakes with
aftershock seismicity within 3 km of each profile are shown at different depths.
Because of less than one hour occurrence in time for the two Chia-Yi
earthquakes, the Coulomb stress changes of these two events are considered
simultaneously to represent the final Coulomb stress change after the 22nd
October, 1999.
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(a)
(b)
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(c)
Figure4 The changes of Coulomb failure stress base on (a) the model by Ji et al.
(2003), (b) three-segments model, and (c) one-segment model, respectively,
associated with the three-month aftershock seismicity after Chi-Chi earthquake.
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