Distribution and Triggering Threshold of Non-Volcanic Tremor Near Anza, Southern California

Distribution and Triggering Threshold of Non-Volcanic Tremor Near Anza, Southern California Waveform examples of Denali tremor on station RDM that is triggered by the passing surface waves of the Denali earthquake. The upper panel shows the Denali earthquake recorded on the vertical component of RDM. The region that is expanded in the lower panels is highlighted in red. The lower panels span 250 seconds and show all three components (vertical, fault parallel, and fault perpendicular). The orange curves show the surface waves of the earthquake in nm/sec and the black curves show the data filtered between 2-8 Hz (amplitude is exaggerated by 20,000).
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To study the distribution and characteristics of non-volcanic tremor in Southern California, we use broadband data collected by the Southern California Seismic Network (SCSN) surface stations near Anza, California and five Plate Boundary Observatory (PBO) borehole stations. To determine the stress amplitude and orientation needed to trigger tremor, we examined 41 teleseismic earthquakes chosen with epicentral distances greater than 1900 km, from diverse azimuths and Mw over 7.0 from 2001 to 2008. We found that only the 2002 Mw7.8 Denali earthquake, with the largest surface wave amplitudes of all of the teleseismic events, triggered detectable tremor. We are currently determining more precise locations of individual tremor bursts in the of Denali-triggered NVT using a template-matching method [Shelly et al., 2009]. The templates will be used to precisely locate the tremor and to examine the spatial and temporal evolution of triggered tremor. Once the tremor are located, we will determine the precise stress pertubation caused by the Denali earthquake at the tremor hypocenter.We will then compare the triggering threshold for tremor to the stress perturbation from teleseisms that trigger local earthquakes on the San Jacinto Fault. From this study we hope to illuminate differences in the response of earthquakes and tremor to stress pertubations.
</p><p>References
</p><p>Shelly, D. R., Ellsworth, W. L., Ryberg, T., Haberland, C., Fuis, G. S., Murphy, J., Nadeau, R. M., and Burgmann, R. (2009), Precise location of San Andreas Fault tremors near Cholame, California using seismometer clusters: Slip on the deep extension of the fault, Geophys. Res. Lett., 36, L01303.
</p><p>Acknowledgements: This work is supported by NSF (EAR0943892) and SCEC (09054).</p>

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