HR: 0800h
AN: T11C-1266    [Abstracts]
TI: The Seismicity of Stable Continental Regions
AU: * van Lanen, X
EM: lanx@geo.vu.nl
AF: US Geological Survey, 345 Middlefield rd. MS 977, Menlo Park, CA 94025 United States
AU: * van Lanen, X
EM: lanx@geo.vu.nl
AF: Vrije Universiteit, De Boelelaan 1105, Amsterdam, 1081 Netherlands
AU: Mooney, W D
EM: mooney@usgs.gov
AF: US Geological Survey, 345 Middlefield rd. MS 977, Menlo Park, CA 94025 United States
AB: The large impact on humans of large magnitude earthquakes in stable continental regions provides a strong motivation to study the systematic nature of their occurrence, to improve the assessment of seismic hazards. Unfortunately, limited historical information of these events complicates studies to better understand these events. The existing main hypotheses to explain their occurrence are (1) reactivation of zones of weakness; (2) localization of stress by physical stress concentrators; (3) crustal weakening by fluids; (4) anomalous high temperatures; and (5) stress changes due to deglaciation or sediment loading. In this study stable continental seismicity patterns were compared with potential field data (Bouguer gravity and aeromagnetic anomaly maps are made). The study cannot disprove any of the existing hypotheses for the occurrence of these events, but it is possible to evaluate some of them. A significant portion of stable continental seismicity follows long linear geophysical trends (500-2000 km) that are correlated with major tectonic features, such as rifted margins and suture zones. The correlation of seismicity with localized stress concentrators is not consistent with this observation, which rather supports the zone of weakness hypothesis. However, in several cases of seismicity not observed in linear trends, the localized stress concentrator hypothesis is instead favorable. Rifted margins commonly have both sedimentary loads and high-density mafic lower crust, both of which provide a stress perturbation. The observed correlation with rifted margins is strong in Australia but less pronounced for eastern North America and is therefore not uniform. The correlation of seismicity with geophysical anomaly maps is an effective means of testing the multiple hypotheses that have been advanced for the genesis of earthquakes in Stable Continental Regions. We favor the view that multiple hypotheses are valid for stable continental earthquakes. Additional studies will help better our assessment of seismic hazards in Stable Continental Regions.
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
DE: 8110 Continental tectonics--general (0905)
DE: 8123 Dynamics, seismotectonics
DE: 7209 Earthquake dynamics and mechanics
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting