HR: 1400h
AN: G33A-06    [Abstracts]
TI: Seismicity variations associated with aseismic transients, Guerrero, Mexico, 1995- 2006
AU: * Liu, Y
EM: liu@esag.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 29 Oxford Street, Pierce Hall 327, Cambridge, MA 02138, United States
AU: Larson, K M
EM: kristinem.larson@gmail.com
AF: Department of Aerospace Engineering Sciences, University of Colorado, UCB 429, Boulder, CO 80309, United States
AU: Rice, J R
EM: rice@esag.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 29 Oxford Street, Pierce Hall 327, Cambridge, MA 02138, United States
AU: Rice, J R
EM: rice@esag.harvard.edu
AF: School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Pierce Hall 224, Cambridge, MA 02138, United States
AB: Aseismic transients with no obvious relation to large earthquakes are a newly recognized mode of deformation along subduction zones, transform plate boundaries and mega-landslide faults. Stressing in the up-dip seismogenic zone is increased due to down-dip slow slips, and it can be made more prone to failure in a large thrust earthquake. Thus, it is important for seismic hazard assessment, to search and identify patterns of spatiotemporal seismicity variation associated with transients and, in some cases, tremors. The Guerrero, Mexico, region is chosen for this study, because of the long-term (over 10 years, continuous and campaign) geodetic observation and abundance of seismicity in the shallow subduction zone. We search the GCMT (Global Centroid Moment Tensor) and NEIC (National Earthquake Information Center) catalogs for seismic events between 1995 and 2006 within the area of latitude 16 to 20N and longitude 98 to 102W, which covers the region affected by major transients since 1996. Earthquake depth is limited to be above 100 km, to roughly include events related to the shallow subduction process. A completeness magnitude of Mc ~ 4.5 is determined, for the NEIC events, based on the maximum likelihood method. Three large transients in 1998, 2001-2002 and recently 2006 [K. Larson, this meeting] are all temporally correlated with higher seismic rates in the studied area. Particularly, we found that transients are either preceded by normal-faulting earthquakes, presumably in the subducting slab given their large epicentral distance from the trench, or followed by shallow thrust-faulting earthquakes close the trench, although the GCMT and NEIC epicenters may vary by tens of km. In some cases, such as the transient from October 2001 to April 2002, both clusters are found bordering the transients, suggesting that the transient may act as a connection in stress transfer [much like the deep slip mechanism for transfer by Dmowska et al. (1988)]. The beginning of the 2006 transient coincided with two normal-faulting earthquakes in February and March, 2006. Thrust earthquakes are found to follow the 1996 and 1998 transients. Although so far no thrust earthquakes have been reported in GCMT after the 2006 transient, the NEIC catalog does show a cluster of seismicity with epicenters close to the trench, thus up-dip in the seismogenic zone. We also perform numerical simulations in the framework of rate and state-dependent friction to model subduction earthquake sequences and aseismic transients. When the normal-faulting earthquake is treated as a stress perturbation to the subduction interface, sequential aseismic transients can be triggered, and the timing of the next large thrust earthquake is affected by three factors, namely, when, where and how large is the perturbation.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 7215 Earthquake source observations (1240)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 8034 Rheology and friction of fault zones (8163)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Geodesy [G]
MN: 2007 Joint Assembly