evidence on non-self-similarity source scaling in cluster earthquakes yen-yu lin 1, kuo -fong ma 1,...
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Evidence on non-self-similarity source scaling in cluster earthquakes
Yen-Yu Lin1, Kuo -Fong Ma1, Hiroo Kanamori2, Teh-Ru Song3, Nadia Lapusta2, Victor Tsai2
1Department of Earth Sciences, National Central University, Taiwan2Seismological Laboratory, California Institute of Technology, USA
3Department of Earth Sciences, University College London, UK
IES 2014/3/19
Earthquake self-similarity????
2
Smaller earthquake
Larger earthquake
r1
r2
Dimension(Circular)
Source time function
1 1wT r
Constant rupture speed
(Aki, 1967)1 2r r
Seismic waveforms
1/30r M shorter P-dur
longer P-dur
Similar Q structure
1/30wT M
wrup
rT
V
2 2wT r
Cluster with constant P-durations
Cluster A
P-phase durations Pdur = 0.07s (~15Hz)Magnitude variationMwe 0.27 to 1.97Filter: Notch filter 60Hz
0.27
1.97
TCDP Borehole seismometersInstrument responseNatural frequency: 4.5HzDamping: 0.29Gain: 100
Sampling rate for analysis1000 p/s before 2008(Nyquist frequency 500Hz)200 p/s after 2008(Nyquist frequency 100Hz)
Corrections before analysis- Instrument response- Galperin angle - Orientation (Lin et al., 2012)
5
Earthquake Clusters
-2006/11~2007/12 (14 months)- Correlation coefficient (3 comp.) > 0.8-130 clusters (2~11 events)- Mwe 0.0~2.0 (S-wave max. amp.)- Located 7 clusters (A-G) (> 4 events) by stacked waveforms
6
Magnitudes estimation
Magnitude variation for the located clusters
8
Seismic clusters- finite P duration0.27
1.97
0.49
1.62
0.35
1.32
9
Instrument problem? NO!
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( ) ( ) ( )V f S f B f
( ) ( ) ( )
( ) ( ) ( )ak a ak
bk b bk
V f S f B f
V f S f B f
0( ) ( )bk b akV f M B f
0
( )
( )ak a
bk b
V f S
V f M
( ) 2 ( ) ( )V f fiCS f F f
1 1 ( )( )
2 ( )
V fS f
fi C F f
Analysis 1 : Empirical Green’s function
Analysis 2 : Futterman Q correction (Futterman, 1962)
within a cluster, Bak(f)=Bbk(f)
For event a and b with receiver k
Observed velocity spectrum:
(Wang et al., 2010; 2012)
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Analysis 1 : Empirical Green’s function
Tw=0.010~0.024 s Source dimension=20~50m
Power of 0.04(1/20)~0.10(1/10)
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Analysis 2 : Futterman Q correction
1 1 ( )( )
2 ( )
V fS f
fi C F f
Q=202 & Q=101
Tw=0.020~0.054 s (a constant for each cluster)Source dimension=40~110m
Q=202
Q=101
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8 1/302.4 10wT M
Comparison to earthquake self-similarity empirical relation (9.2>M>6.5)
Source scaling for the clusters
(Duputel et al., 2013)
Clusters with the constant P-wave durations observations break down the earthquake self-similarity behavior.
Power of 0.04(1/20)~0.10(1/10)
Constant rupture speed “a characteristic length “
Rupture speed and source dimension
a constantwrup
rT
V It can be constrained by
source time function estimations.
0r M 0if rupV M
If α=1/3, earthquake self-similarity!But, selection of α can be arbitrary!- Any specified α could also be another possible model to explain
the unique observations.
Summary
- We discovered 3 clusters with constant P-phase durations (Pdur) for events Mw 0.5 to 2.0 in TCDPBHS records, which had been shown to be natural events from deformed zone of decollement.
- The constant P-phase durations observations in the clusters break down the earthquake self-similarity behavior of Tw ∝ Mo(1/3) as examined by both the empirical Green’s function and Futterman Q correction analyses based on assumption of a constant rupture speed.
- A potential model to explain the constant Pdur phenomenon is an existence of a characteristic length on the fault, limiting the duration of the source time function.
- The difference in high frequency component between smaller and larger events might be due to the heterogeneity of fault.
- If not characteristic length related, another possibility is the significant difference in rupture speed among the cluster events.
Thank you very much!
Analysis 1 : Empirical Green’s function