Earthquake swarms in South America

Abstract

S U M M A R YWe searched for earthquake swarms in South America between 1973 and 2009 using the global Preliminary Determination of Epicenters (PDE) catalogue. Seismicity rates vary greatly over the South American continent, so we employ a manual search approach that aims to be insensitive to spatial and temporal scales or to the number of earthquakes in a potential swarm. We identify 29 possible swarms involving 5-180 earthquakes each (with total swarm moment magnitudes between 4.7 and 6.9) within a range of tectonic and volcanic locations. Some of the earthquake swarms on the subduction megathrust occur as foreshocks and delineate the limits of main shock rupture propagation for large earthquakes, including the 2010 M w 8.8 Maule, Chile and 2007 M w 8.1 Pisco, Peru earthquakes. Also, subduction megathrust swarms commonly occur at the location of subduction of aseismic ridges, including areas of long-standing seismic gaps in Peru and Ecuador. The magnitude-frequency relationship of swarms we observe appears to agree with previously determined magnitude-frequency scaling for swarms in Japan. We examine geodetic data covering five of the swarms to search for an aseismic component. Only two of these swarms (at Copiapó, Chile, in 2006 and near Ticsani Volcano, Peru, in 2005) have suitable satellite-based Interferometric Synthetic Aperture Radar (InSAR) observations. We invert the InSAR geodetic signal and find that the ground deformation associated with these swarms does not require a significant component of aseismic fault slip or magmatic intrusion. Three swarms in the vicinity of the volcanic arc in southern Peru appear to be triggered by the M w = 8.5 2001 Peru earthquake, but predicted static Coulomb stress changes due to the main shock were very small at the swarm locations, suggesting that dynamic triggering processes may have had a role in their occurrence. Although we identified few swarms in volcanic regions, we suggest that particularly large volcanic swarms (those that could be detected using the PDE catalogue) occur in areas of infrequent eruption and may be related to large regional fault zones.

Earthquake Swarms and Slow Slip on a Sliver Fault in the Mexican Subduction Zone

“…The most similar scenario to our findings appears to be in southern Chile where the Liquiñe-Ofqui Fault Zone has been proposed to accommodate the forearc sliver motion associated with oblique subduction (72). There have been reported cases of swarms along the fault that have been attributed to both fluid-induced and tectonic processes where they could be a result of both (50,51,73). The proximity of the swarms to local volcanoes and the Liquiñe-Ofqui Fault Zone complicated determining which process was dominant.…”

Deformation and seismicity near Sabancaya volcano, southern Peru, from 2002 to 2015

“…Ticsani volcano in Peru (175 km SE of Sabancaya) experienced an earthquake swarm but no subsequent eruptive activity [Holtkamp et al, 2011;Jay, 2014]. Between 25 July and 20 October 2005, 31 earthquakes occurred within 50 km of Ticsani with depths less than 50 km and magnitudes ranging from M w 4.0 to 5.3 [Jay, 2014].…”

Monitoring the West Bohemian earthquake swarm in 2008/2009 by a temporary small-aperture seismic array

“…Thus, their characteristics differ from typical mainshock-aftershock sequences at tectonic plate boundaries. Earthquake swarms occur in many regions of the world and are very often related to volcanic activities (Foulger et al 2004;Holtkamp et al 2011) and therefore are mostly treated as local phenomena.…”