TY - JOUR

T1 - Postseismic variations in seismic moment and recurrence interval of repeating earthquakes

AU - Chen, Kate Huihusan

AU - Bürgmann, Roland

AU - Nadeau, Robert M.

AU - Chen, Ting

AU - Lapusta, Nadia

N1 - Funding Information:
We are grateful to Nick Beeler, Justin Rubinstein, Doug Dreger, Ruth Harris, and Zhigang Peng for their helpful discussions. We also thank the two reviewers Naoki Uchida and Terry Tullis for their comments to make this paper better. This work was supported by a Southern California Earthquake Center grant (contribution number 1448 ), the National Science Foundation through grants EAR-0337308 , EAR-0537641 , EAR-0738342 , EAR-0910322 , EAR-0544730 and EAR-0510108 , Taiwan NSC through grants 98-2116-M-003-002 and 99-2116-M-003-006 , and the United States Geological Survey through grant 07HQGR0070 . The Parkfield High Resolution Seismic Network is operated by the University of California, Berkeley Seismological Laboratory with financial support from the US Geological Survey (USGS) through National Earthquake Hazards Reduction Program award 07HQAG0014 . Seismic data are archived at the Northern California Earthquake Data Center. This is Berkeley Seismological Laboratory contribution 10-11. The numerical simulations for this research were performed on the Caltech Division of Geological and Planetary Sciences Dell cluster.

PY - 2010/10/15

Y1 - 2010/10/15

N2 - In laboratory experiments, longer stationary contact time leads to larger seismic moment during repeated ruptures. However, not all observations in natural fault systems agree with the prediction. We analyze a subset of 34 M-0.4-2.1 repeating earthquake sequences (RES) from 1987 to 2009 at Parkfield to examine the variation of their recurrence properties in space and time. Following a 2004 M6 earthquake, many of the repeating events have greatly reduced recurrence intervals (Tr) that systematically increase with time. In addition to this change in timing, we also find systematic changes in seismic moment (Mo), where most sequences experienced an immediate increase in Mo and subsequent decay as Tr approached pre-quake durations. The RES at shallower depth tend to have a larger range in both Tr and Mo, whereas deeper RES show smaller variation. The shallowest RES with the greatest magnitude (M1.8-2.1) among the events we studied reveal a large variation in Tr but small variation in Mo. These observations are qualitatively consistent with earthquake simulations in 3D continuum fault models with rate- and state-dependent friction. In the models, RES are produced on velocity-weakening patches surrounded by velocity-strengthening fault areas. The models show that the degree of postseismic variation in Mo and Tr is a function of radius (r) and nucleation zone size (h*) of the velocity-weakening patch. A ratio of r/. h* ~ 1 produces negative Mo- Tr slopes, whereas larger ratios of r/. h* yield weak positive slopes. Given the same nucleation size h* (i.e., the same frictional properties and effective normal stress), smaller radii and hence smaller seismic moments result in negative Mo- Tr slopes, whereas larger radii and hence larger moments lead to weak positive Mo- Tr slopes, which are consistent with observations. Conversely, with only a small percentage of its slip accumulated seismically, a small asperity appears to grow in Mo under high loading rate, which is contrary to the view that Mo should decrease due to a reduced strength recovery time.

AB - In laboratory experiments, longer stationary contact time leads to larger seismic moment during repeated ruptures. However, not all observations in natural fault systems agree with the prediction. We analyze a subset of 34 M-0.4-2.1 repeating earthquake sequences (RES) from 1987 to 2009 at Parkfield to examine the variation of their recurrence properties in space and time. Following a 2004 M6 earthquake, many of the repeating events have greatly reduced recurrence intervals (Tr) that systematically increase with time. In addition to this change in timing, we also find systematic changes in seismic moment (Mo), where most sequences experienced an immediate increase in Mo and subsequent decay as Tr approached pre-quake durations. The RES at shallower depth tend to have a larger range in both Tr and Mo, whereas deeper RES show smaller variation. The shallowest RES with the greatest magnitude (M1.8-2.1) among the events we studied reveal a large variation in Tr but small variation in Mo. These observations are qualitatively consistent with earthquake simulations in 3D continuum fault models with rate- and state-dependent friction. In the models, RES are produced on velocity-weakening patches surrounded by velocity-strengthening fault areas. The models show that the degree of postseismic variation in Mo and Tr is a function of radius (r) and nucleation zone size (h*) of the velocity-weakening patch. A ratio of r/. h* ~ 1 produces negative Mo- Tr slopes, whereas larger ratios of r/. h* yield weak positive slopes. Given the same nucleation size h* (i.e., the same frictional properties and effective normal stress), smaller radii and hence smaller seismic moments result in negative Mo- Tr slopes, whereas larger radii and hence larger moments lead to weak positive Mo- Tr slopes, which are consistent with observations. Conversely, with only a small percentage of its slip accumulated seismically, a small asperity appears to grow in Mo under high loading rate, which is contrary to the view that Mo should decrease due to a reduced strength recovery time.

KW - Parkfield earthquake

KW - Postseismic process

KW - Rate-and-state models

KW - Recurrence acceleration

KW - Repeating earthquake sequences

UR - http://www.scopus.com/inward/record.url?scp=77958474938&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=77958474938&partnerID=8YFLogxK

U2 - 10.1016/j.epsl.2010.08.027

DO - 10.1016/j.epsl.2010.08.027

M3 - Article

AN - SCOPUS:77958474938

SN - 0012-821X

VL - 299

SP - 118

EP - 125

JO - Earth and Planetary Sciences Letters

JF - Earth and Planetary Sciences Letters

IS - 1-2

ER -