Abstract
A long-standing goal of subduction zone earthquake studies is to determine whether or not there are physical processes that control seismogenesis and the along-strike segmentation of the megathrust. Studies of individual earthquakes and global compilations of earthquakes find favorable comparison between coseismic interplate slip distributions and several different long-lived forearc characteristics, such as bathymetry, coastline morphology, crustal structure, and interplate frictional properties, but no single explanation seems to govern the location and slip distribution of all earthquakes. One possible reason for the lack of a unifying explanation is that the inferred earthquake parameters, most importantly the slip distribution, calculated in some areas were inaccurate, blurring correlation between earthquake and physical parameters. In this paper, we seek to test this possibility by comparing accurate slip distributions constrained by multiple datasets along several segments of a single subduction zone with the various physical properties that have been proposed to control or correlate with seismogenesis. We examine the rupture area and slip distribution of 6 recent and historical large ( M w > 7) earthquakes on the Peru–northern Chile subduction zone. This analysis includes a new slip distribution of the 14 November 2007 M w = 7.7 earthquake offshore Tocopilla, Chile constrained by teleseismic body wave and InSAR data. In studying the 6 events, we find that no single mechanism can explain the location or extent of rupture of all earthquakes, but analysis of the forearc gravity field and its gradients shows correlation with many of the observed slip patterns, as suggested by previous studies. Additionally, large-scale morphological features including the Nazca Ridge, Arica Bend, Mejillones Peninsula, and transverse crustal fault systems serve as boundaries between distinct earthquake segments.
Highlights
7 earthquake physics, because if seismicity is not random, key characteristics of 8 large earthquakes can 9 be forecast through analysis of physical properties.A key obstacle we face in determining whether or not earthquake locations are random along a fault is limited temporal sampling
24 There are at least 4 possible explanations for the lack of a single, global prop25 erty correlating with earthquake parameters: 1) Multiple physical processes influence the rupture; 2) Even if one property dominates seismic patterns in a given subduction zone, spatial variations of this property may limit its influ28 ence over earthquakes elsewhere; 3) The inferred earthquake parameters, most importantly the slip distribution, calculated for some events were inaccurate, blurring any correlation with physical parameters
We focus on the South American subduction zone including central-southern Peru and northern Chile because the area has experienced nine Mw 7 or larger earthquakes between the years 1992–2007 (Figure 1), and several datasets are available to constrain the distribution of coseismic slip on the megathrust
Summary
7 earthquake physics, because if seismicity is not random, key characteristics of 8 large earthquakes (i.e., where they begin, end, and achieve maximum slip) can 9 be forecast through analysis of physical properties.A key obstacle we face in determining whether or not earthquake locations are random along a fault is limited temporal sampling. 24 There are at least 4 possible explanations for the lack of a single, global prop erty correlating with earthquake parameters: 1) Multiple physical processes influence the rupture; 2) Even if one property dominates seismic patterns in a given subduction zone, spatial variations of this property may limit its influ ence over earthquakes elsewhere; 3) The inferred earthquake parameters, most importantly the slip distribution, calculated for some events were inaccurate, blurring any correlation with physical parameters This could be an explanation for the lack of correlation between geologic structures or morphotectonic provinces with earthquakes in southern Chile from 1570–1960
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