The 2007 M7.7 Tocopilla northern Chile earthquake sequence: Implications for along‐strike and downdip rupture segmentation and megathrust frictional behavior

Abstract

[1] In 2007 a M7.7 earthquake occurred near the town of Tocopilla within the northern Chile seismic gap. Main shock slip, derived from coseismic surface deformation, was confined to the depth range between 30 and 55 km. We relocated $1100 events during six months before and one week after the main shock. Aftershock seismicity is first congruent to the main shock slip and then it spreads offshore west and northwest of Mejillones Peninsula (MP). Waveform modeling for 38 aftershocks reveals source mechanisms that are in the majority similar to the main shock. However, a few events appear to occur in the upper plate, some with extensional mechanisms. Juxtaposing the Tocopilla aftershocks with those following the neighboring 1995 Antofagasta earthquake produces a striking symmetry across an EW axis in the center of MP. Events seem to skirt around MP, probably due to a shallower Moho there. We suggest that the seismogenic coupling zone in northern Chile changes its frictional behavior in the downdip direction from unstable to mostly conditionally stable. For both earthquake sequences, aftershocks agglomerate in the conditionally stable region, whereas maximum inter-seismic slip deficit and co-seismic slip occurs in the unstable region. The boundary between the unstable and conditionally stable zones parallels the coastline. We identify a similar segmentation for other earthquakes in Chile and Peru, where the offshore segments break in great M > 8 earthquakes, and the onshore segments in smaller M < 8 earthquakes. Using critical taper analysis, we demonstrate a causal relationship between varying slip behavior on the interface and forearc wedge anatomy that can be attributed to spatial variations in the rate-dependency of friction.Citation: Schurr, B., G. Asch, M. Rosenau, R. Wang, O. Oncken, S. Barrientos, P. Salazar, and J.-P. Vilotte (2012), The 2007 M7.7 Tocopilla northern Chile earthquake sequence: Implications for along-strike and downdip rupture segmentation and megathrust frictional behavior,

High-frequency seismic radiation from Maule earthquake (Mw 8.8, 2010 February 27) inferred from high-resolution backprojection analysis

“…The seismogenic zone has recently been subdivided in a shallower part dominated by co-seismic slip and a deeper part characterized by high-frequency radiation, and the occurrence of major but not great earthquakes in the interseismic period Schurr et al 2013;Yao et al 2013). Our results-with the co-location of aftershocks and the peak of energy emission at the downdip edge of the coseismic slip area -are in line with this general behaviour.…”

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“…This mechanism could be responsible for the correlation of basins with source areas of megathrust earthquakes (Mogi, 1969;Nishenko and McCann, 1979;Wells et al, 2003) and peninsulas with barriers (e.g. Victor et al, 2011;Schurr et al, 2012;Saillard et al, 2017). moreover suggest a feedback between forearc deformation and seismogenesis along the megathrust: accordingly, because the stable wedge part overlying the seismogenic zone in segmented forearcs deforms quasi-elastically, characteristic great earthquakes tend to occur fairly periodically as in simple spring-slider experiments and numerical simulations of the experiments .…”

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“…The role of subducted seamounts in the nucleation and rupture propagation of large subduction earthquakes have been widely discussed (Bilek et al, 2003;Das and Watts, 2009;Dixon and Moore, 2007;Hicks et al, 2012;Schurr et al, 2012;Yang et al, 2013a). A series of earthquakes between 1983 to 1999 along the Costa Rican subduction zone led to the suggestion that spaced isolated seamounts could act as asperities (Bilek et al, 2003).…”