INTRAPLATE MICRO-SEISMICITY IN THE CENTRAL PART OF THE SIERRA MADRE ORIENTAL, MEXICO

Mexico is a seismic country, the major of the activity is present on the pacific shore due to the subduction of Cocos plate beneath North America plate, and nevertheless there are zones within the North America plate that show intraplate earthquakes not related to this plate interaction. This study analyses the possible causes of the intraplate seismicity occurring in the central part of the Sierra Madre Oriental thrust-and-fold belt. The data was obtained by the monitoring of the local seismological network Landa, which has been operated by the Centro de Geociencias-UNAM since November 2007. This network consists of short period seismographs with 4.5 Hz sensors. The seismograms used in this work, correspond to the months between november 2007 and december 2010. A total of 1553 events were processed and located in Seisan, but the total records are 3176 giving the background seismicity rate in this period. Due the limitation of the instruments, many of the events were located by the single station method, to calibrate accuracy of the method events reported by others seismic networks were compared with our solutions. There are also a 150 pairs of doublets located and analyzed. In the study area there has been a few considerable historical events with magnitude 7, some of these produced damages i.e the 1989 Landa earthquake with a 4.6 M destroyed the dome of the local colonial church, nowadays people who lives in the surrounds towns of Landa de Matamoros report “shakes and sounds” on the ground that occur with different space and time distribution, besides the records it is also possible to see cracks in a few buildings across Landa de Matamoros. The epicentral locations are correlated with geological and geophysical maps.