Un aporte a la investigación de métodos de alerta temprana

La charla, organizada por el Programa de Riesgo Sísmico, PRS, y el Programa de Reducción de Riesgos y Desastres, CITRID, ambos de la Universidad de Chile, se efectuó el viernes 25 de agosto en dependencias de la Facultad de Ciencias Físicas y Matemáticas.

La investigación de Simon Guerin-Marthe aporta a la comprensión de los procesos físicos involucrados en el inicio de una ruptura sísmico (inicio del terremoto). Su trabajo analiza los precursores del deslizamiento lento durante la fase de nucleación de un terremoto. Esto es de gran importancia en la investigación de métodos de alerta temprana.

Abstract

Slow slip precursors during the nucleation of earthquakes have potential implications for early-warning systems and probabilistic forecasting. Although most field studies on nucleation focus on foreshocks sequences, recent GPS observations of the 2014 Chile megathrust show a slow slip phase releasing a significant portion of the total moment. Despite hints from theoretical stability analysis (Rice & Ruina, 1983) and modelling (Rubin & Ampuero 2005; Kaneko et al. 2017), it is not fully understood what controls the prevalence and the size of slip in the nucleation process. Here we present laboratory observations of slow slip preceding dynamic rupture, where for the first time we observe a dependence of nucleation size on the loading rate (laboratory-equivalent of tectonic loading rate). The setup is composed of two polycarbonate plates under direct shear with a 30 cm slip interface. Rupture position, stresses and slip are monitored at high frequency using a high-speed camera, strain gages and laser positioning system placed along the simulated fault interface. The results of our laboratory experiments are in agreement with the pre-slip model proposed by Ellsworth (1995) and subsequently observed in laboratory experiments (Nielsen et al. 2010; Latour et al. 2013), which show a slow slip followed by an acceleration up to dynamic rupture velocity. However, further complexity arises from the effect of (1) rate of shear loading and (2) small-scale inhomogeneities on the fault surface. In particular, the nucleation length shrinks (from 3 cm to 0.5 cm) when loading is increased (from 10 -2 MPa/s to 1 MPa/s).