HR: 0800h
AN: T41A-1164    [Abstracts]
TI: Characteristics and Possible Triggering Relationship of Earthquakes at the Pacific Transform Faults
AU: * Gregg, P M
EM: trish@whoi.edu
AF: MIT/WHOI Joint Program, WHOI Dept. Geology & Geophysics MS 24, Woods Hole, MA 02139
AU: Lin, J
EM: jlin@whoi.edu
AF: Woods Hole Oceanographic Inst., WHOI Dept. Geology and Geophysics MS 22, Woods Hole, MA 02139
AU: Smith, D K
EM: dsmith@whoi.edu
AF: Woods Hole Oceanographic Inst., WHOI Dept. Geology and Geophysics MS 22, Woods Hole, MA 02139
AB: We utilize hydroacoustic data collected between May 1996 and November 2001 by NOAA/PMEL's Equatorial Pacific autonomous hydrophone array to investigate seismicity patterns at six transform faults near the equatorial Pacific Ocean: the Clipperton, Siqueiros, Quebrada, Discovery, Gofar, and Yaquina. The calibrated seismicity rate of a transform fault, when normalized by the transform fault length, changes from one transform to the other. The Clipperton transform fault, the only transform in our study with a single fault segment, has undergone tectonic compression during the last 0.5 Ma and has the lowest hydroacoustically recorded seismicity rate of the six transforms. Based on earthquakes recorded in the Harvard CMT catalog, however, Clipperton has had the highest amount of cumulative energy released of the 6 transforms from 1976 to 2004. The last Mw=6.6 occurred in May 1995, immediately preceding the deployment of the NOAA hydrophone array. One possibility for the current low seismicity rate is that Clipperton transform is currently in a seismic quiet period. In contrast, the Siqueiros, Quebrada, Discovery, and Gofar transforms all consist of multiple transform segments separated by intra-transform spreading centers. These transforms have undergone tectonic extension during the last 0.5 Ma and they each exhibit relatively high seismicity rates during the hydrophone monitoring period. Siqueiros, Discovery and Gofar show moderate seismic moment release for the last 28 years. On the other hand, Yaquina transform, thought to be a hybrid transform/non-transform offset (Lonsdale, 1989), has a low hydroacoustically recorded seismcity rate and a low moment release for the last 28 years. Through correlating hydrophone data to teleseismically recorded events, we have located several moderate size earthquakes on the Siqueiros, Discovery, and Gofar transform faults. Eight of the nineteen moderate size events ($>$ 5.3 Mw) recorded in the Harvard CMT catalog between 1996-2001 occurred closely in space and time, suggesting the possibility of earthquake interaction. Stress calculations were carried out for several pairs of the moderate size events. The relatively close correlation of the calculated Coulomb stress changes with the observed spatial and temporal variations in the main events and with the aftershock activities provides strong evidence for both static and dynamic stress interaction of earthquakes along the transform faults. Furthermore, aftershock sequences associated with the moderate size earthquakes are relatively short, lasting less than 2 days and have fewer than 120 events, thus showing considerable differences from typical aftershock sequences of continental earthquakes, which last significantly longer and have several times more aftershock events.
DE: 8123 Dynamics, seismotectonics
DE: 3025 Marine seismics (0935)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting