SCEC Award Number 17240 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Systematic Detection of Repeating Earthquakes Along the Central San Jacinto Fault
Investigator(s)
Name Organization
Zhigang Peng Georgia Institute of Technology
Other Participants Dongdong Yao (GT graduate student)
One SCEC SURE intern
SCEC Priorities 3a, 3b, 3d SCEC Groups Seismology, FARM, CS
Report Due Date 03/15/2019 Date Report Submitted 05/06/2019
Project Abstract
 We perform a systematic detection of potential repeating earthquakes along the central segment of the San Jacinto Fault (SJF). Starting with ~33,100 earthquakes listed in the relocated catalog of Southern California, we cross-correlate all event pairs with hypocentral distance less than 20km using an 8-s long window around P wave on vertical channels of stations within 50km. A repeating pair is registered when 5 or more stations have cross-correlation coefficients above 0.95. We further group all repeating pairs into different sequences. Currently, we observed a total number of ~11,500 repeating pairs, containing ~6,550 events with magnitude between 0 and 3. This relatively high percentage (~20%) of repeating events might be caused by including micro-earthquakes from adjacent but not overlapping rupture patches. Nevertheless, the mere existence of repeating earthquake pairs indicates potential creeping deformation along the central SJF. The temporal distribution of repeating earthquakes might reveal a combination of both characteristic repeating earthquakes driven by fault creep and repeaters modulated by transient slip episodes, such as continuing afterslip following several moderate-size mainshocks along the SJF. Our study suggests that obtaining complete repeating sequences can provide additional constraints on possible creeping behaviors along the SJF.
Intellectual Merit While some studies have suggested possible “deep creep” along the central SJF, it is relatively difficult to quantify their spatio-temporal extent with surface geodetic instruments. Because fault creep is capa-ble of driving small repeating earthquakes, we can potentially use them as a proxy to study fault creep behaviors at seismogenic depth. Hence, systematic detection of repeating earthquakes in Southern Cali-fornia can help to “constrain the active geometry and rheology of the ductile roots of fault zones” (P3.b).
Broader Impacts An improved understanding of creep behaviors at deep fault roots help to constrain the depth extent of large earthquake ruptures and resulting ground motions. This project supported GT graduate student Dongdong Yao, and the work is included in his 2018 Ph.D. thesis. He is in the process of developing a tutorial on how to detect repeating earthquakes from massive amount of seismic data.
Exemplary Figure Figure 2. (a) Waveforms for a repeating event pair in the SJF. Network and station names and the corre-lation-coefficients are labeled on both sides, respectively. (b) Waveform within a repeating sequence recorded at station AZ.RDM. The corresponding magnitudes and occurrence times are marked.