Source model of the 2007 M_w 8.0 Pisco, Peru earthquake: Implications for seismogenic behavior of subduction megathrusts

Abstract

[1] We use Interferometric Synthetic Aperture Radar, teleseismic body waves, tsunami waveforms recorded by tsunameters, field observations of coastal uplift, subsidence, and runup to develop and test a refined model of the spatiotemporal history of slip during the M w 8.0 Pisco earthquake of 15 August 2007. Our preferred solution shows two distinct patches of high slip. One patch is located near the epicenter while another larger patch ruptured 60 km further south, at the latitude of the Paracas peninsula. Slip on the second patch started 60 s after slip initiated on the first patch. We observed a remarkable anticorrelation between the coseismic slip distribution and the aftershock distribution determined from the Peruvian seismic network. The proposed source model is compatible with regional runup measurements and open ocean tsunami records. From the latter data set, we identified the 12 min timing error of the tsunami forecast system as being due to a mislocation of the source, caused by the use of only one tsunameter located in a nonoptimal azimuth. The comparison of our source model with the tsunami observations validate that the rupture did not extend to the trench and confirms that the Pisco event is not a tsunami earthquake despite its low apparent rupture velocity (<1.5 km/s). We favor the interpretation that the earthquake consists of two subevents, each with a conventional rupture velocity (2-4 km/s). The delay between the two subevents might reflect the time for the second shock to nucleate or, alternatively, the time it took for afterslip to increase the stress level on the second asperity to a level necessary for static triggering. The source model predicts uplift offshore and subsidence on land with the pivot line following closely the coastline. This pattern is consistent with our observation of very small vertical displacement along the shoreline when we visited the epicentral area in the days following the event. This earthquake represents, to our knowledge, one of the best examples of a link between the geomorphology of the coastline and the pattern of surface deformation induced by large interplate ruptures.

Superficial simplicity of the 2010 El Mayor–Cucapah earthquake of Baja California in Mexico

“…3c). Such an anti-correlation has been observed in a number of previous studies [14][15][16][17] suggesting that some of the aftershocks release residual strains near the patches of high slip.…”

Control of asperities size and spacing on seismic behavior of subduction megathrusts

“…As in our models, the Pedernales earthquake features the rupture of two adjacent asperities that activated in two distinct phases of the same earthquake (i.e., the second asperity has been activated 25 s from earthquake initiation) [Nocquet et al, 2016]. Also the M w 8.0 Pisco earthquake, which occurred in 2007 along the Peruvian megathrust, is characterized by rupturing of two distinct asperities with slip activation on the second asperity delayed by 60 s from earthquake initiation [Sladen et al, 2010]. Another typical example of recent megathrust earthquake characterized by two slip patches is the M w 8.8 Maule earthquake that struck the central Chile megathrust in 2010 [Moreno et al, 2012;Lorito et al, 2011].…”

Supervised Method of Landslide Inventory Using Panchromatic SPOT5 Images and Application to the Earthquake-Triggered Landslides of Pisco (Peru, 2007, Mw8.0)

“…The areas covered by the images have been chosen to encompass most of the areas visited by the field survey after the earthquake. [37]. Indeed, these aftershocks are clustered updip of the hypocenter and south of the Paracas Peninsula, at least 60 km far from the main area of landslide ( Figure 1).…”

“…The epicenter was 18 km deep and ruptured the megathrust along the subduction zone of Nazca and southern American plates [38]. It broke a fault segment of 170 km, parallel to the coast, composed of 2 main asperities [37]. The analysis of the accelerogram registered in a radius of 200 km showed the complexity of this rupture [39].…”

“…Summary of the SPOT5 image pairs used in this study: (a) temporal baseline and (b) corresponding images coverage. The 1 m contour of slip distribution on the fault during the Pisco earthquake (orange line) is extracted from Sladen et al [37]. The white dots represent the landslides identified with the field inventory [36].…”