Estimation of the paleoepicentral area from the spatial gradient of deformation in lacustrine seismites (Tierras Blancas Basin, Mexico)

• Published in: Quaternary international Vol. 219; no. 1; pp. 66 - 78
• Main Authors: Rodríguez-Pascua, M.A., Garduño-Monroy, V.H., Israde-Alcántara, I., Pérez-López, R.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.06.2010
• Subjects: Freshwater; Mexico
• ISSN: 1040-6182; 1873-4553
• DOI: 10.1016/j.quaint.2009.11.006

A new methodology is introduced to estimate the most probable epicentral area for a paleoearthquake interpreted from seismites within a Quaternary basin. Seismites were described from various detailed stratigraphic logs within the Tierras Blancas Basin (TBB), a Pleistocene lacustrine area located in the central part of the Trans-Mexican Volcanic Belt (TMVB). The lacustrine landscape evolution of TBB has been determined by the recent fault activity of the Morelia-Acambay Fault System (MAFS). The TBB is bounded by active normal faults striking E-W. This fault activity has generated soft-sediment deformation structures, sand, silt and gravel dikes, pillows, diapirs, and decametric slumps, disturbing the sedimentary infilling. From these seismites and their stratigraphic spatial correlation, five strong-moderate paleoearthquakes (E1–E5) have been established in the basin. The spatial distribution of these seismites exhibits a gradient of perturbation defined by the intensity of deformation. Three different degrees of intensity deformation (DDI) are associated with the liquefacted grain size sediments: I (silt liquefaction), II (silt and sand liquefaction), and III (silt, sand and gravel liquefaction). This spatial gradient indicates an increase of the energy involved from the seismic activity, related with the proximity of the source. Mapping the boundaries among these zones of deformation and interpolation of each DDI limit for paleoearthquake E4 was used to construct paleoseismic isolines of deformation as a potential indicator of the most probable paleoepicentral zone. A 1.5 km 2 elongate zone oriented NNW-SSE is the potential paleoepicentral area associated with paleoearthquake E4 within the TBB.