Study of the structure and seismicity of the February 27, 2010 Chile Mw 8.8 earthquake rupture zone
Final Report Abstract
The main objective of the project was to further our understanding of the relationships between great earthquakes, the structure of convergent margins and postseismic relaxation processes using the earthquake sequence along the Southern Chilean margin which started on 27 February 2010 with the Mw 8.8 Maule earthquake. This sequence provides an opportunity to image the aftershock activity in great detail and structure of the rupture zone of a great earthquake. We used data of a dense network of 142 seismograph stations installed by various international teams shortly after the mainshock along the entire 500 km long rupture zone. The first 12 months of the 22 months reporting period were focussed on solving technical issues in order to automatically detect and locate the dense aftershock sequence, necessary because of the high number of events and stations. We applied automated P and S-picking algorithms to the complete local seismicity catalogue. We found that the automated P and S phases from picking algorithms perform are comparable to a human analyst, but the “hit-rate” is less than the rate from a human analyst because of the (conservative) tendency of the algorithm to downgrade a number of high quality picks. This phase resulted in a local event catalogue where the aftershock seismicity is related to the structure of the Chilean Forearc. Seismicity occurs in various groups along the Forearc. The most unusual properties of the aftershock seismicity are the observation of a pronounced normalfaulting sequence at the northern limit of the 2010 rupture with ~10.000 locally detected aftershocks and the band of plate interface seismicity in 40-50 km depth which is clearly separated from the main interface at shallower depth. In the second year of the project we focused on the relation of aftershock seismicity and the postseismic deformation observed by GPS. We suggest a method (Lange et al., 2014) to map the ‘afterslip to aftershock ratio’ along the convergent margin by comparing cumulative number of events with temporal-spatial afterslip models. In the last year of the project source properties of aftershocks were inverted. Focal mechanisms highlight the correlation of thrust focal mechanisms with the 3D slab model geometry in the area. The analysis of depth and magnitude dependence of the normalized source duration (NSD), following an approach proposed for strong and global earthquakes in subduction zones, indicates that the correlation between NSD and depth holds also for smaller magnitude events at local and regional scales. The tendency of increased NSD observed for shallow depths (<20 km) is most likely due variations of rigidity rather then from special frictional conditions along the plate interface.
Publications
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(2012), Aftershock Seismicity of the 27 February 2010 Mw 8.8 Maule Earthquake Rupture Zone, Earth and Planetary Science Letters, 317-318C, pp. 413-425
Lange, D., Tilmann, F., Barrientos, S. E., Contreras-Reyes, E., Methe, P., Moreno, M., Heit, B., Agurto, H., Bernard, P., Vilotte, J.-P., Beck, S.
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(2012), Mantle subducting slab structure in the region of the 2010 M8.8 Maule earthquake (30–40°S), Chile, Geophysical Journal International
Pesicek, J. D., Engdahl E.R., C.H. Thurber, H.R. DeShon, Lange, D.
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(2013), A high-resolution, timevariable afterslip model for the 2010 Maule Mw=8.8, Chile megathrust earthquake, Earth and Planetary Science Letters, 383, pp. 26-36
Bedford, J.R., Moreno, M., Baez, J.-C., Lange, D., Tilmann, F., Rosenau, M., Heidbach, O., Oncken, O., Ryder, I., Bevis, M., Bartsch, M., Vigny, C.
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(2014), Comparison of postseismic afterslip models with aftershock seismicity for three subductionzone earthquakes: Nias 2005, Maule 2010 and Tohoku 2011, Geophysical Journal International, 199(2), 784-799
Lange, D., Bedford, J. R., Moreno, M., Tilmann, F., Baez, J.C., Bevis, M., Krüger, F.
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(2014), Splay fault activity revealed by aftershocks of the 2010 Mw=8.8 Maule earthquake, Central Chile. Geology
Lieser, K., Grevemeyer, I., Lange, D., Flueh, E., Tilmann, F., Contreras-Reyes, E.
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(2014). High-frequency seismic radiation from Maule earthquake (Mw 8.8, 27/02/2010) inferred from high-resolution backprojection analysi, Geophysical Journal International, 199(2), 1058-1077
Palo M.,Tilmann, F., Krueger F.,Ehlert L., Lange D.
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Systematic Changes Of Earthquake Rupture With Depth: A Case Study From The 2010 Mw 8.8 Maule, Chile, Earthquake Aftershocks Sequence, Bulletin of the Seismological Society of America, 105(5), 2015 (12 S.)
Sen, T.A., Heimann, S., Cesca, S., Lange, D., Dahm, T., Tilmann, F.
