HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) References Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Delouis, B. Articles by Cisternas, A. Search for Related Content GeoRef GeoRef Citation

The M_w = 8.0 Antofagasta (northern Chile) earthquake of 30 July 1995: A precursor to the end of the large 1877 gap

Institut de Physique du Globe, 5 rue R. Descartes, 67084 Strasbourg Cedex, France
ORSTOM, 213 rue Lafayette, 75480 Paris Cedex 10, France
Departamento de Geofísica Universidad de Chile, Casilla 2777, Santiago, Chile

Abstract

An M_w = 8.0 earthquake occurred on 30 July 1995 in the Antofagasta region (northern Chile). The main rupture, corresponding to thrust faulting, developed from 10 to 50 km in depth along the subduction interface between the Nazca and the South American plates. The 1995 earthquake took place just south of the large seismic gap where a great earthquake (M = 9) had occurred in 1877. Most of the 1995 rupture was located within a local network consisting of nine short-period stations that had been previously installed at the southern end of the 1877 gap, and the aftershock sequence could be accurately monitored. Little destruction resulted from the 1995 earthquake in spite of its large size. Ground acceleration in Antofagasta reached 29% of gravity. A tsunami wave, 2 to 2.5 m high, was observed along the coast from Mejillones to Taltal. One strong foreshock (M_w = 6.2) occurred in the 1995 hypocentral region 6 months before the main event.

Body-wave modeling of broadband seismograms from the global network, along with the analysis of the aftershock distribution, allows us to propose a well-constrained model for the whole rupture process. Some additional details of the rupture were obtained from an accelerometer record at Antofagasta. The main rupture started as a double even with thrust mechanism below the southern part of the Mejillones peninsula, and it propagated southward in a N200°E direction with an average velocity of 2.8 km/sec. It ended near the trench in normal faulting. The total rupture area and seismic moment are 185 x 90 km² and 1.2 x 10²⁸ dyne-cm, respectively. The aftershock distribution delineates a well-defined rupture surface along the subduction interface. The distribution of epicenters during the first 20 h of aftershock activity shows a sharp northern boundary beneath the Mejillones peninsula. Hence, the 1995 main rupture did not propagate north of the Mejillones peninsula into the 1877 gap. Aftershocks during the following 2 weeks indicate a growth of the initial rupture zone toward the north. The mechanisms of the strongest aftershocks are similar to that of the mainshock. The down-dip termination of the main rupture corresponds to the maximum depth (50 km) of the region that had been identified as the locked part of the subduction interface from the analysis of the microseismicity recorded by the local network prior to the 1995 event.

A well-constrained dislocation model is proposed for the 1995 main rupture, which produces surface displacements in good agreement with available observations of coastal uplift and GPS measurements. The dislocation model, as well as Global Positioning System (GPS) measurements, indicate that the 1995 earthquake generated E-W extension in the coastal region of Antofagasta. The Atacama fault, located 40 to 50 km above the 1995 main rupture, showed small fresh surface ruptures near Sierra Remiendos (70 km to the SSE of Antofagasta) with a maximum vertical offset of 20 cm. This offset corresponds to normal faulting, which is in agreement with the E-W co-seismic extension.

The Mejillones peninsula appears to be the surface expression of a barrier that interrupted the propagation of the 1995 rupture to the north into the region of the 1877 gap. Modeling of static stress changes induced by the Antofagasta earthquake indicates an increase in compressive stresses along a direction transverse to the trench immediately to the north of the 1995 rupture surface. Thus, the chances for the reactivation of the 1877 gap after this event are greater now.

This article has been cited by other articles:

				B. Delouis, M. Pardo, D. Legrand, and T. Monfret The Mw 7.7 Tocopilla Earthquake of 14 November 2007 at the Southern Edge of the Northern Chile Seismic Gap: Rupture in the Deep Part of the Coupled Plate Interface Bulletin of the Seismological Society of America, February 1, 2009; 99(1): 87 - 94. [Abstract] [Full Text] [PDF]

				H. Hebert, A. Sladen, and F. Schindele Numerical Modeling of the Great 2004 Indian Ocean Tsunami: Focus on the Mascarene Islands Bulletin of the Seismological Society of America, January 1, 2007; 97(1A): S208 - S222. [Abstract] [Full Text] [PDF]

				R. W. Allmendinger, G. Gonzalez, J. Yu, G. Hoke, and B. Isacks Trench-parallel shortening in the Northern Chilean Forearc: Tectonic and climatic implications Geological Society of America Bulletin, January 1, 2005; 117(1-2): 89 - 104. [Abstract] [Full Text] [PDF]

				S. Husen and E. Kissling Postseismic fluid flow after the large subduction earthquake of Antofagasta, Chile Geology, September 1, 2001; 29(9): 847 - 850. [Abstract] [Full Text] [PDF]

				B. Delouis and D. Legrand Focal mechanism determination and identification of the fault plane of earthquakes using only one or two near-source seismic recordings Bulletin of the Seismological Society of America, December 1, 1999; 89(6): 1558 - 1574. [Abstract] [PDF]

				Y. Y. Kagan and D. D. Jackson Worldwide doublets of large shallow earthquakes Bulletin of the Seismological Society of America, October 1, 1999; 89(5): 1147 - 1155. [Abstract] [PDF]

				K. Gouget, P. F. Ihmle, J. Campos, and J.-P. Montagner Self-consistent retrieval of source parameters using mantle waves Bulletin of the Seismological Society of America, August 1, 1998; 88(4): 995 - 1002. [Abstract] [PDF]