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

rTV

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!

10

( ) ( ) ( )V f S f B f

( ) ( ) ( )( ) ( ) ( )

ak a ak

bk b bk

V f S f B fV f S f B f

0( ) ( )bk b akV f M B f

0

( )( )

ak a

bk b

V f SV f M

( ) 2 ( ) ( )V f fiCS f F f

1 1 ( )( )2 ( )

V fS ffi 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 ffi 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

rTV

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