The M_W=8.1 Antofagasta (North Chile) Earthquake of July 30, 1995: First results from teleseismic and geodetic data

Abstract

A strong (Mw = 8.1) subduction earthquake occurred on July 30, 1995 in Antofagasta (northern Chile). This is one of the largest events during this century in the region. It ruptured the southernmost portion of a seismic gap between 18°S and 25°S. In 1992 we had used GPS to survey a network with about 50 benchmarks covering a region nearly 500 km long (N‐S) and 200 km wide (E‐W). Part of these marks were re‐surveyed with GPS after the 1995 earthquake. Comparison with 1992 positions indicate relative horizontal displacement towards the trench reaching 0.7 m. The inland subsided several decimeters. The Mejillones Peninsula was uplifted by more than 15 cm. Teleseismic body‐wave modelling of VBB records gives a subduction focal mechanism and source time function with three distinct episodes of moment release and southward directivity. Modelling the displacement field using a dislocation with uniform slip in elastic half‐space suggests a rupture zone with 19°–24° eastward dip extending to a depth no greater than 50 km with N‐S length of 180 km and an average slip of about 5 m. The component of right‐lateral slip inferred both from the teleseismic and geodetic data does not require slip partitioning at the plate boundary. That the well‐constrained northern end of the 1995 rupture zone lies under the southern part of the Mejillones Peninsula increases the probability for a next rupture in the gap north of it.

Field observations of seismic velocity changes caused by shaking-induced damage and healing due to mesoscopic nonlinearity

“…The M W 8.4 Arequipa earthquake in 2001 could therefore have introduced a velocity change of 1.2 per cent leading to the linear trend in the velocity changes that we observe during the study period. As the rupture duration of the Antofagasta earthquake was shorter (60 s; Ruegg et al 1996) compared to the one of the Arequipa earthquake but with a similar maximal shaking (estimated by extrapolation), we conclude that the 1995 earthquake seems less plausible to induce a velocity change of 2.5 per cent which would be necessary to cause the linear trend. Considering that the effects of the different earthquakes are superimposed it seems very likely that the linear trend, which was empirically introduced to fit the data, also consistently results from our model.…”

Testing stress shadowing effects at the South American subduction zone

“…The rupture length and location for recent strong events were taken from Barrientos & Ward (1990) for the M9.6 1960 Valdivia earthquake, Delouis et al (1997) for the M7.6 1987 earthquake near Antofagasta, Ruegg et al (1996) for the M8.0 1995 Antofagasta earthquake, Pritchard & Simons (2006) for the M9.6 1960 Valdivia earthquake, Chlieh et al (2011) for the M8.4 2001 Arequipa earthquake, the rupture plane of which extends well into our area of investigation, Schurr et al (2014) for the M7.9 2007 Tocopilla earthquake, Yue et al (2014) for the M8.8 2010 Maule earthquake, Geersen et al (2015) and Schurr et al (2014) for the M8.1 2014 Iquique earthquake, and Tilmann et al (2016) for the M8.2 2015 Illapel earthquake. In the case that the rupture length is not constrained by observations, we estimate rupture lengths from the scaling relation of Blaser et al (2010) for dip-slip inter-plate earthquakes.…”

A model of deep crustal fluid flow following the Mw = 8.0 Antofagasta, Chile, earthquake

“…Rupture plane location of the M W = 8.0 Antofagasta, Chile, earthquake after Ruegg et al [1996]. The fault extends 180 km along strike and 80 km in the dip direction and appears at the interface between oceanic and Andes continental crust inside the seismogenic zone.…”