The Mw 8.8 Maule, Chile earthquake of 27 February 2010 is estimated to be the sixth largest earthquake globally since 1900. The Maule earthquake is the most recent in a long history of large and great subduction megathrust earthquakes along the central and southern Chile convergent plate boundary. It ruptured the megathrust segment just to the north of the great 1960 Chile earthquake, the largest earthquake ever instrumentally recorded, filling in and apparently extending beyond an identified seismic gap. Existing and new local/regional datasets for Chile provide key data allowing us to constrain marginwide velocity structure and pre- and post-seismic earthquake locations with a greater accuracy than has been achieved before for this region and move toward a better understanding of how this convergent plate boundary fault releases strain and evolves over the seismic cycle. Among the key issues to be addressed are the following: (1) What are the updip, downdip, and along-strike limits of aftershockactivity, and how do aftershocks spatially relate to prior seismicity and main shock rupture pattern? (2) Do structural variations in the upper and lower plates affect main shock rupture and aftershock distribution? (3) Are there identifiable gaps in the background seismicity and/or aftershock distribution that could be potentially filled by a major earthquake?

The project involves the following steps: First, they will carefully reprocess the available ISS, ISC, and PDE data for the region encompassing the Chile subduction zone from about 40° S to 30° S, extending as far back in time as 1918, using stringent event quality criteria to produce significantly improved single event hypocenters for the global data. Next, they will gather all available regional arrival time data, including data from new and preexisting Chilean, U.S. and international deployments, and then combine them with the groomed global data to produce a comprehensive and internally consistent margin-wide earthquake catalog. Finally, they will use the complete dataset for (a) single-iteration nested regional-global tomography, (b) robust multiple-iteration nested regional-global tomography, and (c) teleseismic double-difference tomography and relocation.

The goal of this project is to investigate the Mw 8.8 Maule, Chile earthquake of 27 February 2010, its aftershock sequence, and the nature of the plate boundary fault on which it occurred. The Maule earthquake, estimated to be the sixth largest earthquake globally since 1900, is the most recent in a long history of large and great earthquakes along the central and southern Chile convergent plate boundary. It occurred just to the north of the great 1960 Chile earthquake, the largest earthquake ever instrumentally recorded. In this project, researchers will form a comprehensive and internally consistent catalog of earthquakes for analysis. Using these data, researchers will determine precise earthquake locations for the 2010 aftershock sequence and prior earthquakes and image the 3D structure of the plate boundary region and the fault on which the 2010 great earthquake occurred. These results will allow us to address significant scientific questions that will help us better understand why great earthquakes occur where they do, when they do.

Project Report

We developed a new seismic image of the subduction zone where the 2010 magnitude 8.8 Maule, Chile earthquake occurred. We combined seismic wave arrival time data from regional and distant (teleseismic) earthquakes and initially used a conventional multi-scale tomographic method. The new image revealed the detailed structure of the subducting slab as it transitions from a flat-lying slab to the north to a more normally dipping slab in the Maule region. Here the transition is found to be a continuous bend. In contrast, to the south of the Maule region, the slab appears to be torn. We next applied a new, "double-difference" (DD) tomographic method to an expanded dataset for the same region. The DD method uses differential seismic wave arrival times and an iterative solution to improve the clarity with which seismicity features can be defined and sharpen the seismic image in the areas where the earthquakes have occurred. The results show that the velocity anomaly patterns from the multiple iteration solution are quite similar in pattern to the single iteration results but with increased amplitudes in the slab and other features (see first figure). Our locations (panel C in the second figure) are greatly improved compared to the NEIC and EHB results (panels A and B, second figure) and show a quality comparable to that from a detailed regional study (panel D, second figure). The inversion code, named teletomoDD, should have broad applicability to many regions of interest around the world.

Agency
National Science Foundation (NSF)
Institute
Division of Earth Sciences (EAR)
Type
Standard Grant (Standard)
Application #
1114245
Program Officer
Eva E. Zanzerkia
Project Start
Project End
Budget Start
2011-07-01
Budget End
2014-06-30
Support Year
Fiscal Year
2011
Total Cost
$147,678
Indirect Cost
Name
University of Wisconsin Madison
Department
Type
DUNS #
City
Madison
State
WI
Country
United States
Zip Code
53715