COSMISMIC STRATIGRAPHY IN LACUSTRINE SEQUENCES OF THE CVTM, SAN PEDRO EL ALTO CASE

La estratigraf\ueda cos\uedsmica se define como el registro sedimentario modificado por la actividad s\uedsmica ocurrida en el momento de su dep\uf3sito, sin expresi\uf3n superficial aparente. Esta actividad influye en la evoluci\uf3n de la cuenca y a su vez se ve reflejada en el paisaje. En cuencas lacustres de origen tect\uf3nico o vulcanotect\uf3nico como las del Cintur\uf3n Volc\ue1nico TransMexicano (CVTM), los efectos de cambio clim\ue1tico, tasas de sedimentaci\uf3n, influencia antropog\ue9nica, entre otros, son factores importantes en su evoluci\uf3n, no obstante, deben considerarse factores ex\uf3genos como sismicidad y vulcanismo, los cuales modifican las condiciones paleoecol\uf3gicas y paleolimnol\uf3gicas de la cuenca. Por lo anterior, es necesario llevar el estudio bajo dos puntos de vista, el estratigr\ue1fico y el s\uedsmico ya que adicionalmente a las rupturas cos\uedsmicas, las propiedades f\uedsicas de los materiales son modificadas por los efectos primarios y secundarios de un sismo. El graben de Acambay, perteneciente al CVTM y una de las zonas representativas de la actividad s\uedsmica reciente en el pa\ueds, almacena el registro sedimentario de los eventos que han sido parte de la evoluci\uf3n de las cuencas en el Cuaternario. Tal registro se corrobora mediante la deformaci\uf3n de los estratos que en algunas ocasiones y sitios espec\uedficos han desarrollado estructuras que ofrecen informaci\uf3n sobre el tipo de evento que las gener\uf3. La cuenca de San Pedro El Alto, presenta una serie de secuencias sedimentarias en donde se han registrado eventos s\uedsmicos que han influenciado su evoluci\uf3n. En este trabajo se pretende definir la evoluci\uf3n del paisaje s\uedsmico de la cuenca ligada al Graben de Acambay con base en el estudio detallado de la estratigraf\ueda y la identificaci\uf3n de paleosismos (estratigraf\ueda cos\uedsmica)

Coseismic stratigraphy in Holocene lacustrine sequences of San Pedro El Alto, Estate of Mexico

The Mexican Volcanic Belt contains a series of coseismic registers in lacustrian sequences in which the consequence of seismic collisions due to fault movements left deformed structures. The scope of this paper is to define the geological and biological evolution of the lacustrian depression of San Pedro el Alto, immersed in the Acambay graben. The area presents morphological evidence of current coseismic ruptures such as vertical height differences, fault edges, structural drainage control and counterslopes. The natural conditions, as well as the time and space relations in which seismic events took place will be demonstrated, underpinned by a detailed study of the area\u2019s stratigraphy and fossil diatoms. Furthermore, the fluctuations in the level of the lake can provide guidelines to understand the environmental factors linked to coseismal ruptures occurred during the Miocene

PRELIMINARY GEOMORPHOLOGIC AND PALEOSEISMIC INVESTIGATIONS ALONG THE AGUA FRIA FAULT IN THE LOS AZUFRES VOLCANIC EDIFICE: AN ATTEMPT TOWARDS SEISMIC HAZARD ASSESSMENT IN CENTRAL MEXICO

The Morelia\u2013Acambay Fault System (MAFS) is a < 260 km long fault system bounded by Acambay Graben to the east and the Cuitzeo Graben to the west. Till date, most of the paleoseismic investigations were focus on the epicentral area of known crustal earthquakes, in the Acambay and Cuitzeo grabens. However there are several undocumented crustal faults between these grabens that are long enough to generate large magnitude earthquakes. In this study, we used a multidisciplinary approach (Geomorphology and Paleoseismology) to characterize the earthquake history of the Agua Fria Fault, one of the largest faults of the MAFS central segment. The fault traces and associated landforms like triangular facets, ponding and scarps were mapped using high resolution satellite imageries and topographic data. The geomorphological data indicate that the fault scarp is at least 13 km long striking E-W and is height varies from few meters to hundreds of meters. Three trenches were excavated at three different sites along the Agua Fria fault. Preliminary results indicate that various earthquakes were produced by this fault during Pleistocene