The Mw=8.8 Maule earthquake off the coast of Chile on February 27, 2010 is the 5th largest megathrust earthquake ever to be recorded and the 2nd largest to be recorded by modern digital seismic networks. Immediately following the Maule earthquake, teams of seismologists from Germany, France, the UK, and the US, working with seismologists in Chile, coordinated resources to deploy both broadband and short period seismometers and accelerometers above the rupture zone to capture aftershocks associated with this significant earthquake. Data recorded from these stations will be combined to produce an open international community data volume providing an unprecedented opportunity to investigate processes associated with great earthquakes and to image the anatomy of a subduction zone. A defining characteristic of the Maule aftershock investigations has been collaboration, at both national and international levels. The original involvement in the data collection by US teams grew voluntarily out of the IRIS community, and the rationale of greater efficiencies through cooperation was readily adapted by the five international groups working in the region.
In this project the researchers will carry out a broad but interrelated spectrum of seismic analyses to the Maule international seismic data set, along with a reanalysis of a selection of data collected in the rupture zone prior to the earthquake, to address some of the fundamental scientific objectives that motivated the initial data collection. These objectives fall into two general categories: (1) rupture processes of megathrusts, and (2) active tectonics and dynamics of an oceanic-continental (Andean) margin. They intend to produce an internally consistent set of data products across a range of analytical techniques. The PIs will share graduate students and scheduling extended visits to each others labs, thereby exposing students to a significantly broader range of experience than most students typically enjoy. Finally, they plan to engage our international colleagues by sharing some analysis tasks of mutual interest. Data products generated by this study will be made available to the broader international community via a dedicated web site.
This main objective of this project were to analyze seismograms of aftershocks of the 2010 Mw8.8 Maule (Chile) earthquake in order to recover more detail about the nature of the rupture zone and the overriding South American plate. This project was a collaborative effort of several seismologists in the US, Germany, the UK, France, and Chile. Among the more significant data analysis results to come out of our joint efforts, we were able to generate the following principal products: (1) a comprehensive event catalog of locations and focal mechanisms, (2) 3D elastic wave images of the subuction zone, (3) a shear wavespeed model for most of the Chilean crust, (4) a map of crustal thickness in the rupture area, and (5) a detailed image of the region encompassing the Pichilemu event, which was the largest aftershock of the Maule earthquake. Among our principle findings was an image of an irregularity on the slab interface that strongly influenced the generation of aftershocks; we infer that this irregularity is due to the subduction of a seamount. We were also able to map the rupture of the Pichilemu normal fault, which turned out to be two reactivated faults at varying strike. Maps of the elastic wavespeed variations are of both academic and practical interest. From an academic point of view they allow us to make inferences about the evolution of the Andes; practically they allow us to quantitatively model the ground motion that results from large events. The PI authoring this summary (Roecker) was engaged primarily in waveform modeling of both teleseismic and local earthquake seismograms. The teleseismic results were inconclusive, largelyl because the numerous local events interfered with most of the usable signal. However, we discovered that the migration of local earthquake coda can be an effective tool for imaging interfaces in the upper plate such as the Moho and large scale faults. Broader impacts: Perhaps the most significant boarder impact of this project is that it serves as an example of how an international collaboration can work in an open data environment; this is a mode of research which to our knowledge has never been attempted before in the geosciences. The success of this project should encourage similar types of collaborations in the future as it is clear that they can geneate results that go well beyond what individual investigators can accomplish with such datasets. Several graduate students were involved in this project; the PI advised a masters level student on waveform imaging and part of the coda migration work contributed to the PhD work of another graduate student. The masters student is now working in Chile towards her PhD with one of our Chilean colleagues from this project, applying what she learned to the Pisagua region of Chile, where the next very large earthquake is expected. Results of this project have been disseminated in publications and talks at professional meetings; we also conducted an extended workshop with our Chilean colleagues on the 2013 anniversary of the Maule event.
