Dynamic triggering of earthquakes and tremors in Taiwan
Date Issued
2011
Date
2011
Author(s)
Yeh, Ting-Chen
Abstract
The discovery of deep-seated tremor opened up a new window into the complex processes below the base of the seismogenic zone. As tremor and associated low frequency earthquakes appear to represent shear failure capable of producing seismic radiation, a brittle failure model is generally proposed as the physical mechanism. It is possible that very high fluid pressure on discrete fault patches or distinct lithologic heterogeneity facilitate slip in an otherwise ductile shear regime. Tremor in Taiwan was triggered by teleseismic surface waves from distant events [Peng and Chao, 2008; Tang et al., 2010; Chao et al.,
in review, 2011], where a threshold of dynamic stress 7–8 kPa is inferred. Built on the previous research, in this study we refine the triggering threshold and further explore the similarity/difference in triggering response of tremor and earthquakes. This research illuminates the differences in response of shallow and deep portions of the fault to dynamic stress changes induced by distant earthquakes. We found 4 of 21 Sumatra Mw ≧ 7.0 earthquakes since 2000 triggered tremor, while 3 events triggered small earthquake within the surface wave train. The dynamic stress calculation indicates that the triggered stress induced by surface waves need to be above 2.86 kPa and 0.0454 kPa for immediate triggering of tremor and earthquakes, respectively. The tremors are confined in a small area underneath south of Central Range, below the seismogenic zone where the earthquake swarms and higher Vp/Vs ratio are located. This suggests the possible connection between tremor activity and fluid process. The dominant role of small shear-stress perturbations in stimulating the tremor but not crustal earthquakes indicates a very weak fault zone with extremely low effective normal stress. Likely due to near lithostatic pore pressures in the tremor source region.
Subjects
dynamic triggering
triggered tremor
triggered earthquakes
Type
thesis
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