Recent earthquakes thatoccurred between 1973-2002 (USGS), illustrate the diffuse shallow nature of plateau sesimic activity. Except in the western and eastern syntaxis of Indo-Asian collision, most of the earthquakes are located at less than 15 km (figure 8). The shallow depth of the events indicates a relatively warm lithosphere with shallow brittle-ductile transition beneath the plateau.
Figure 8. Depth distributed epicenter locations of earthquakes occurred between 1973-2002 [USGS].
Centroid Moment Tensor (CMT) solutions of earthquakes with M > 5, shows 3 different types of active faulting (figure 9). Thrust mechanisms mainly concentrated over main Himalayan thrust front and north of Tibetan plateau with SW-NE oriented compression directions. Although plate motions indicates ongoing collision, earthquakes related to the subduction of Indian plate do not display a clear Benioff zone. They also disappear with increasing latitudes. On the other hand, shallow thursting on the northern margin proves ongoing shortening associated with fold and thrust belts at the north. Extension related active normal faulting mainly took place in southern Tibet where topography reaches maximum values. Except one mantle earthquake, depth of these events are consistent with a depth of faulting less than to 15 km and they give W-E directed extension. In central and eastern Tibet, focal mechanisms indicate sinistral strike-slip faulting along series of large fault systems. The pressure axes of these events also have orientations similar to the active thrusting which agrees with slip partitioning. It is worth noting that magnitudes of some strike-slip reached up to 8 and caused extensive damage.
Figure 9. CMT solutions of Indo-Asian earthquakes that occurred during between 1977-2000 with M > 5 [Harvard, CMT catalog].
A) Tectonics & Geology B) Seismicity C) GPS D) Seismic profiles & Tomography
E) Gravity F) Anisotropy G) Paleomagnetism H) Geochemistry I) MT studies
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