HR: 14:55h
AN: S43D-06    [Abstracts]
TI: Shallow Seismicity in Stable Continental Regions (SCRs): Implications for Earthquake Hazards
AU: * Klose, C D
EM: cklose@ldeo.columbia.edu
AU: Seeber, L
EM: nano@ldeo.columbia.edu
AB: A world-wide compilation of strong (M_w 4.5-8.0) and well constrained earthquakes in stable continental regions (SCRs) reveals a bimodal depth distribution with a very shallow upper crustal component. SCR-earthquake ruptures are confined within the upper or the lower thirds of the crust (0-10 km or 20-35 km). Thus, while the mid crust accounts for much of the moment released in active continental regions (ACRs; excluding regions where tectonics has changed crustal thickness), the same depth range in SCRs shows a minimum of seismicity. This remarkable difference has been partly hidden by a tendency to overestimate hypocentral depths in SCRs, where instrumental coverage tends to be sparse. The upper 5 km of ACR-crust are generally weak and seismically opaque, thus releasing relatively little seismic moment and attenuating seismic energy coming from below. In contrast, the upper SCR-crust is generally strong and many large SCR-earthquakes nucleate close to the surface, with severe implications for hazard. On the other hand, the tendency of SCR-earthquakes to occur in sequences and to rupture downward offers an opportunity for improving hazard estimates; after an earthquake occurs the probability of another earthquake increases dramatically in a source area with no prior seismicity. Such a probability can be quantified from available data. The aforementioned issues become more important, when human activities are more likely to cause significant stress changes in the depth range for nucleation of SCR-earthquakes than for ACR-earthquakes. A world-wide compilation of human triggered earthquakes due to geomechanical pollution confirms the argument of shallow earthquake nucleation in SCRs.
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Seismology [S]
MN: Fall Meeting 2005