Evidence that the 2008 Mw 7.9 Wenchuan Earthquake Could Not Have Been Induced by the Zipingpu Reservoir

Abstract

According to the Coulomb failure criterion the variation of either shear stress, normal stress, or pore pressure can affect the occurrence, or not, of earthquakes. Abnormalseismicity increasesaroundreservoirsareoftenthoughttobeinducedbythe water impounded behind the dam, which leads to nearby increases in crustal pore pres- sure and Coulomb stress, and so may promote the nearby faults to fail. To investigate how much the Zipingpu reservoir, whose dam is just a few hundred meters from the Longmen Shan fault, influenced the 12 May 2008 Wenchuan earthquakeM w 7.9, we calculatedtheCoulombstressvariationinducedbythefillingoftheZipingpureservoir, which began in October 2005. We also analyzed the correlation between local seismi- cityvariationsandtheinducedCoulombstressvariations.BoththecalculatedCoulomb stress variations and the observed seismicity analysis suggest that the probability that the huge Wenchuan earthquake,M w 7.9, was induced by the Zipingpu reservoir is very low. The filling of the Zipingpu reservoir could only result in an increase in the rate of shallowearthquakeswithhypocenterdepthsmallerthan5kmnearthereservoirregion.