Spatial and temporal variations in earthquake stress drop on Gofar Transform Fault, East Pacific Rise : implications for fault strength
Moyer, Pamela A.
Boettcher, Margaret S.
McGuire, Jeffrey J.
Collins, John A.
MetadataShow full item record
KeywordEarthquake stress drop; Oceanic transform faults; Fault zone damage; Rupture dynamics; Earthquake swarms; Seismic coupling
On Gofar Transform Fault on the East Pacific Rise, the largest earthquakes (6.0 ≤ MW ≤ 6.2) have repeatedly ruptured the same portion of the fault, while intervening fault segments host swarms of microearthquakes. These long‐term patterns in earthquake occurrence suggest that heterogeneous fault zone properties control earthquake behavior. Using waveforms from ocean bottom seismometers that recorded seismicity before and after an anticipated 2008 MW 6.0 mainshock, we investigate the role that differences in material properties have on earthquake rupture at Gofar. We determine stress drop for 138 earthquakes (2.3 ≤ MW ≤ 4.0) that occurred within and between the rupture areas of large earthquakes. Stress drops are calculated from corner frequencies derived using an empirical Green's function spectral ratio method, and seismic moments are obtained by fitting the omega‐square source model to the low frequency amplitude of the displacement spectrum. Our analysis yields stress drops from 0.04 to 3.2 MPa with statistically significant spatial variation, including ~2 times higher average stress drop in fault segments where large earthquakes also occur compared to fault segments that host earthquake swarms. We find an inverse correlation between stress drop and P wave velocity reduction, which we interpret as the effect of fault zone damage on the ability of the fault to store strain energy that leads to our spatial variations in stress drop. Additionally, we observe lower stress drops following the MW 6.0 mainshock, consistent with increased damage and decreased fault strength after a large earthquake.
Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 123 (2018): 7722-7740, doi:10.1029/2018JB015942.
Suggested CitationJournal of Geophysical Research: Solid Earth 123 (2018): 7722-7740
Showing items related by title, author, creator and subject.
Stress triggering in thrust and subduction earthquakes and stress interaction between the southern San Andreas and nearby thrust and strike-slip faults Lin, Jian; Stein, Ross S. (American Geophysical Union, 2004-02-03)We argue that key features of thrust earthquake triggering, inhibition, and clustering can be explained by Coulomb stress changes, which we illustrate by a suite of representative models and by detailed examples. Whereas ...
Boettcher, Margaret S. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2005-06)The relatively simple tectonic environment of mid-ocean ridge transform fault (RTF) seismicity provides a unique opportunity for investigation of earthquake and faulting processes. We develop a scaling model that is ...
Roland, Emily C.; McGuire, Jeffrey J. (John Wiley & Sons, 2009-06-04)Swarm-like earthquake sequences are commonly observed in a diverse range of geological settings including volcanic and geothermal regions as well as along transform plate boundaries. They typically lack a clear mainshock, ...