SCEC Award Number 11082 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Dynamic triggering of shallow earthquakes and deep tremor in Southern California
Name Organization
Zhigang Peng Georgia Institute of Technology
Other Participants Kevin Chao
Chastity Aiken
SCEC Priorities A5, A6, A11 SCEC Groups Seismology, FARM, EFP
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
Our project focused on understanding the physical mechanisms and necessary conditions for dynamic triggering of deep tremor and shallow earthquakes in California. Peng et al. [2010] examined triggered earthquakes in the Coso geothermal regions and triggered tremor around Parkfield-Cholame following the 2010 Mw8.8 Chile earthquake. They found that both triggered earthquakes and tremor were consistent with frictional failure at different depths on critically-stressed faults under the Coulomb failure criteria. Peng et al. [2011] found the first evidence of dynamic triggering of microearthquakes at Coso by multiple surface waves of the Chile earthquake. Aiken et al. [in prep, 2012] systematically analyzed triggered microearthquakes in three geothermal regions (Long Valley, Coso and Geysers) in California and found different triggering behaviors. Chao et al. [2012] found that tremor in the San Jacinto Fault in Southern California (SC) and the Calaveras Fault in Northern California (SC) was not easily triggered by teleseismic earthquakes, when compared with the Parkfield-Cholame section of the San Andreas Fault in Central California (CC). The lack of widespread triggered tremor in NC and SC is not simply a consequence of their different background noise levels from CC, but rather reflects different background tremor rates in these regions. Peng et al. [2011] found that artificial high-frequency signals could be generated from the analysis procedure when computing spectrograms. Peng et al. [2012] and Kilb et al. [2012] also converted seismic data into sounds and animations to help convey information about dynamic triggering of tremor and microearthquakes to general audience.
Intellectual Merit It is directly relevant to the primary missions of the Fault and Rupture Mechanics (FARM) group: “Understand implications of slow events and non-volcanic tremors for constitutive properties of faults and overall seismic behavior.”. It also directly addresses the following research objective outlined in the SCEC3 RFP: (1) A11. “Constrain absolute stress and understand the nature of interaction between the faulted upper crust, the ductile crust and mantle, and how geologic history helps to resolve the current physical properties of the system”. Finally, it is also relevant to the long-goals of the Earthquake Forecasting and Predictability group on “Investigate stress-mediated fault interactions and earthquake triggering and incorporate the findings into time-dependent forecasts for Southern California.”
Broader Impacts The PI Peng has given multiple seminars and talks on the findings of non-volcanic tremor in Central and southern California at various institutions during SCEC3. These include the USGS Menlo Park (Summer, 2010), China Earthquake Administration in 2008 and 2011, and Caltech Seismolab in Spring 2009.

In addition, PI Peng has hosted a total of 5 SCEC summer interns during SCEC 3 (Summer Ohlendorf, Summer 2007; Amanda Fabian and Lujendra Ojha, Summer 2009; Adrian Doran and Meghan Fisher, summer, 2010). They have been working on various projects that are directly or partially funded by SCEC3. Their work has been presented at previous SCEC, AGU and SSA annual meetings, and some have resulted in peer-review publications [e.g., Chao et al., 2012; Kilb et al., 2012].

Funding from this project provided partial support for the GT graduate student Kevin Chao, who has become an export in studying triggered tremor in Taiwan, California, and New Zealand. He is expected to defend his Ph.D. thesis in May and his work in California triggered tremor [Chao et al., 2012] will become a chapter of his thesis. In addition, it provides summer support to the second-year graduate student Chastity Aiken to work on comparison of triggered microearthquakes in geothermal regions in California.
Exemplary Figure Figure 1. (Left) Maximum peak ground velocity (PGV) of surface wave (horizontal axis) in transverse component versus median amplitude of the 2-8 Hz 3-components band-pass-filtered envelope functions during the surface waves (a-c) and signal to noise ratio (SNR) (d-f) at broadband stations PKD, RDM, and MHC in Central California (CC), Southern California (SC), and Northern California (NC), respectively. (Right) Top: 2–8-Hz band-pass-filtered vertical seismograms showing the move-out of tremor triggered by the Denali fault earthquake along the San Jacinto fault (SJF) in southern California (SC). The seismograms are plotted along the SJF strike. Bottom: A comparison between the velocity and the 2–8 Hz band-pass-filtered seismograms recorded at the broadband station RDM. From Chao et al. [2012].