Análisis Cinemático del Sistema de Fallas de Billecocha, utilizando evidencia Geomorfológica y Geofísica, Cantón Cotacachi, Provincia de Imbabura

Abstract:

While several destructive earthquakes have occurred in the history of Ecuador, not all have been able to be assigned to a specific fault. This is the case of the Ibarra earthquake of 1868 (7.0 y 7.3 Mw Beauval et al., 2010), which devastated nearby towns and resulted in more than 20 thousand fatalities. The distribution of intensities (Beauval et al., 2010) suggests an epicenter near the Billecocha Fault System (BFS). Prior work suggests that these structures are extensional in origin, probably generated via isostatic adjustment due to melting since the last period of glaciation ~6 – 10 Ka BP (Ego et. al., 1996). If true, this idea implies that these are non-tectonic structures and mostly devoid of the ability to produce strong future earthquakes. To this end, in this study we seek to better characterize the nature of the fault system from both field, seismic, and remote sensing techniques. The BFS is located northwest of Cotacachi county at approximately 4000 meters above sea level and distributed over an area 5 km wide and 20 km long. Detailed geomorphological lineament analyses show abundant evidence of transcurrent motions. These include the presence of moraines with lateral displacements, strike-slip compressive structures, and drainages either offset horizontally or completely cut and abandoned. Seismic refraction lines and ground-penetrating radar (GPR) reveal layers between 2 - 6 m thick cut by a southeast dipping plane. Additionally, a fault-perpendicular trench was dug and exhibits a sedimentary pack consisting of mostly volcanic sediments with interspersed pumice and fluvio-glacial deposits displaced by various fault planes. Colluvial wedges with at least 3 offsets are also present, the last of which actually reaches the surface. The analysis carried out in this study is relevant for the quantification of the area seismic risk.

Año de publicación:

2020

Keywords:

• SISTEMA DE FALLAS
• GEOFISICA
• GEOLOGIA

Fuente:

rraae