Joint modeling of teleseismic and tsunami wave observations to constrain the 16 September 2015 Illapel, Chile, M_w 8.3 earthquake rupture process

Abstract

The 16 September 2015 Illapel, Chile, Mw 8.3 earthquake ruptured ~170 km along the plate boundary megathrust fault from 30.0°S to 31.6°S. A patch of offshore slip of up to 10 m extended to near the trench, and a patch of ~3 m slip occurred downdip below the coast. Aftershocks fringe the large‐slip zone, extending along the coast from 29.5°S to 32.5°S between the 1922 and 1971/1985 ruptures. The coseismic slip distribution is determined by iterative modeling of teleseismic body waves as well as tsunami signals recorded at three regional DART stations and tide gauges immediately north and south of the rupture. The tsunami observations tightly delimit the rupture length, suppressing bilateral southward extension of slip found in unconstrained teleseismic‐wave inversions. The spatially concentrated rupture area, with a stress drop of ~3.2 MPa, is validated by modeling DART and tide gauge observations in Hawaii, which also prove sensitive to the along‐strike length of the rupture.

Subduction zone megathrust earthquakes

“…This observation has been supported by aftershock catalogs for many of the M > 8 earthquakes, such as the recent Sumatra (e.g., Hsu et al, 2006), Chile (Hayes et al, 2014b;Yue et al, 2014b;Li et al, 2016), and Tohoku (e.g., Asano et al, 2011) earthquakes. The 2013 Santa Cruz Islands earthquake appears to have had few aftershocks on the megathrust fault, and this event may have triggered an adjacent aseismic slip episode following the main shock (Hayes et al, 2014a).…”

“…Efforts are under way to synthesize the accumulated data sets (e.g., Kanamori, 2014;Lay, 2015;Ye et al, 2016bYe et al, , 2016cDenolle and Shearer, 2016;Meier et al, 2017;Melgar and Hayes, 2017;Hayes, 2017), and we will not attempt to summarize the multitude of studies. Large shallow coseismic slip occurred in the 2015 Illapel (e.g., Li et al, 2016;Melgar et al, 2016), 2011 Tohoku (e.g., Lay et al, 2011b;Iinuma et al, 2012;Ozawa et al, 2012;Satake et al, 2013;Romano et al, 2014;Bletery et al, 2014;Melgar and Bock, 2015;Lay, 2017), 2010 Maule (e.g., Vigny et al, 2011;Yue et al, 2014b;Yoshimoto et al, 2016;Maksymowicz, et al, 2017), and 2004 Sumatra (e.g., Ammon et al, 2005;Rhie et al, 2007;Fujii and Satake, 2007) events, accompanying slip on the downdip portions of the megathrusts. In other cases, such as the 2014 Iquique, Chile (e.g., Lay et al, 2014;Hayes et al, 2014b), 2012 Nicoya, Costa Rica (e.g., Yue et al, 2013;Liu et al, 2015), 2003 Tokachi-oki, Japan (e.g., Miyazaki and Larson, 2008;Romano et al, 2010), and 2007 Pisco, Peru, ruptures (e.g., Lay et al, 2010a;Sladen et al, 2010), slip was concentrated on the central or deeper portion of the rupture zone, with no shallow coseismic slip.…”

Development and application of a tsunami fragility curve of the 2015 tsunami in Coquimbo, Chile

“…Even though the modified Li et al (2016) model overestimates the maximum amplitude at the DART buoy, the simulation exhibits a very good agreement with the tsunami record in Coquimbo. When the M w = 8.3 models proposed by Ruiz et al (2016) and Shrivastava et al (2016) were analyzed, it was possible to observe a good agreement at the DART buoy and Valparaiso tide gauge, although the amplitude in Coquimbo is underestimated by more than a meter.…”

“…Since the inundation heights were measured at a few locations across the inundation area and there is a lack of tsunami traces in the wetland, interpolation of tsunami height may not be suitable; therefore, the tsunami heights were obtained from tsunami numerical simulation of the 2015 event. We tested four available finite-fault models, namely those of Li et al (2016), Ruiz et al (2016), Okuwaki et al (2016) and Shrivastava et al (2016), and the best fit was selected according to tide gauges in Coquimbo and Valparaiso and DART buoy 32402. Once the best slip model was selected, we used the field measurements of inundation height and runup to select an appropriate dry-land roughness coefficient.…”

“…Once the best slip model was selected, we used the field measurements of inundation height and runup to select an appropriate dry-land roughness coefficient. The model proposed by Li et al (2016) is obtained from iterative modeling of teleseismic body waves as well as tsunami records at DART buoys. Since the magnitude of the proposed model is M w = 8.21, the slip distribution was multiplied by a factor of 1.38; thus, all events have the same magnitude: 8.3.…”