An earthquake doublet in Ometepec, Guerrero, Mexico

                                       Reporter : Chang-Wei Tsao

                                          Abstract

                 An earthquake doublet was occurred near Ometepec, Guerrero, Mexico
                 which was considered a high seismic potential area. Those two event were
                 very close to each other for not only the scale of the magnitude but also
                 temporal separation. To know why the earthquake doublet occurred is 
                 significant for us to understand more about the nucleation of earthquake.
                 Within the research of Luciana Astiz and Hiroo Kanamori, they use two
                 methods to determine the source parameters. From inverting of surface
                 wave data at period 256 sec, the first event, strike = 116°, dip = 77°, slip
                 =88°, and the seismic moment of2.8 * 1026 dyne-cm. For second event,
                 strike = 116°, dip = 78°, slip = 89° and seismic moment of 2.8 * 1026
                 dyne-cm. And from modeling long period P wave, they are able to estimate
                 the seismic moment for those two events. The ratio of the seismic moment
                 from body wave to the that from surface wave is 0.5 for first event ,and 1
                 for second one. These results suggests that the first event involved a deeper
                 asperity. Considering both the seismic moment and first week aftershock
                 area, 3200km, the stress drop is 4 bars, and co-seismic slip is 0.58m. It
                 accounts for about 25% of the total plate motion between the Cocos Plate 
                 and the North America Plate.
                   The other research is to present a new relationship between Ometepec,
                 Guerrero doublet generation and local geological features. The aftershock
                 distribution implicate the presence Cocos subducting plate disruption at the
                 Ometepec, Guerrero area which might be reasonably related to the 
                 nucleation of doublet .

                                          Reference

                 Astiz, L., Kanamori, H., 1984. An earthquake doublet in Ometepec, Guerrero, 
                 Mexico. Phys. Earth Planet Interior 34, 24–45.

                                           (Abstract)(Full text)

                 Jaime Yamamoto, Luis Quintanar, Zenon Jimenez, 2002. Why earthquake doublets 
                 in the Ometepec, Guerrero, Mexico subduction area? Phys. Earth Planet Interior.
                 132, 131–139.

                                           (Abstract)(Full text)