Tectonics and Aftershocks of the Mw=8.8 2010 Chile earthquake rupture area from Oceanbottom Seismometer data
Final Report Abstract
Splay faults, large thrust faults emerging from the plate boundary to the seafloor in subduction zones, are considered to enhance tsunami generation by transferring slip from the very shallow dip of the megathrust onto steeper faults, thus increasing vertical displacement of the seafloor. These structures are predominantly found offshore, and are therefore difficult to detect in seismicity studies, as most seismometer stations are located onshore. The Mw=8.8 Maule earthquake of 27th of February 2010 affected ~500 km of the central Chilean margin. In response to this event, a network of 30 ocean-bottom seismometers was deployed for a 3 month period north of the main shock where the highest co-seismic slip rates were detected, and combined with land station data providing onshore as well as offshore coverage of the northern part of the rupture area. Data were analyzed using an automatic picking engine, identifying more than 83.610 (46.397 on OBS and 37.213 on land stations) first arrival P-wave onset times of 4.592 potential events. In the rupture area of the 2010 Maule main shock, 3.751 local earthquakes were identified and located, with 1.043 events of the quality class “good” or better that were considered for interpretation. For the best 1.043 local earthquakes, S-wave onsets were derived using an automatic picking engine modified for secondary S-waves, providing additional 9.020 S-wave arrival times (3.485 on OBSs and 5.535 on land stations). Data were located in a 2.5D model based on constraints from seismic refraction and wide-angle data from an amphibious experiment crossing the seismic network. The aftershock seismicity in the northern part of the survey area reveals, for the first time, a wellresolved seismically active splay fault in the submarine fore-arc. Application of critical taper theory analysis suggests that in the northernmost part of the rupture zone, co-seismic slip likely propagated along the splay fault and not the subduction thrust fault, while in the southern part it propagated along the subduction thrust fault and not the splay fault. The possibility of splay faults being activated in some segments of the rupture zone but not others should be considered when modeling slip distribution. Seismic tomography based on the aftershock sequence successfully imaged the structural heterogeneity of the area, revealing a number of features, including (i) the high-velocity subducting plate, (ii) the low velocity marine fore-arc with the accretionary prism and the paleo-prism, and (iii) the continental domain. The continental Moho and the mantle wedge are poorly resolved, related to a lack of post-seismic activity in the shallow Wadati-Benioff zone.
Publications
- (2014), Splay fault activity revealed by aftershocks of the 2010 Mw 8.8 Maule earthquake, central Chile, Geology, 42, 823-826
Lieser, K., I. Grevemeyer, D. Lange, E. Flueh, F. Tilmann, E. Contreras-Reyes
(See online at https://doi.org/10.1130/G35848.1) - (2015) After the 2010 Mw 8.8 Maule Earthquake – tectonics in central Chile derived by an automated analysis of aftershocks from an amphibious seismic network, Dissertation der Mathematisch-Naturwissenschaftlichen Fakultät, Christian-Albrechts-Universität, Kiel, pp. 181
Lieser, Kathrin
