Observations and Modeling of Extreme Subduction Earthquakes

Abstract eng:
The 19/09/1985 a Ms 8.1 thrust mechanism subduction superficial (TSS) earthquake occurred in the Mexican Pacific ocean coast with an epicentral distance of 380 km from Mexico City (MC). The estimates of the human and economical losses related to this large event, were of about 30,000 people and more than 6 billion US dollars, the largest share of these were in MC. The largest, Ms 8.2, instrumentally observed TSS earthquake in Mexico, occurred in the Colima-Jalisco region the 3/06/1932, with epicentral distance of about 200 km from Guadalajara (G) in northwestern Mexico. The estimated frequency of occurrence, in Mexico, of these types of events varies from decades to about 100 years and their upper Ms bound are still under discussion. By applying a hybrid method, previously validated for the 19/09/1985 and for the 09/10/1995 Ms 7.6 Colima-Jalisco earthquakes, we generated broadband synthetic accelerograms, expected in MC stiff and compressive soils, and in G sandy soils, associated to extreme seismic scenarios for TSS Mw 8.5 earthquakes. Based on an acceptable risk criteria, in order to minimize the probability of exceedance associated to an expected economical loss of 6.22 Billion US dollars, for the proposed Mw 8.5 MC earthquake scenario, a compressible soil design spectra Sa(5%) ordinate of 1.4g (g=981 cm/s2), seems appropriate (for the 19/09/1985 earthquake the observed Samax(5%) was equal to about 1g). From the information of the construction stock of G, the economical loss, associated to the Mw 8.5 earthquake scenario analyzed amounts to 19 billion US$ dollars.

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