Abstract
This study used the rupture directivity theory to derive the fault parameters of the 2010 Mw 8.8 Chile earthquake on the basis of the azimuth-dependent source duration obtained from the Rayleigh-wave phase velocity. Results revealed that the 2010 Chile earthquake featured asymmetric bilateral faulting. The two rupture directions were N171°E (northward) and N17°E (southward), with rupture lengths of approximately 313 and 118 km, respectively, and were related to the locking degree in the source region. The entire source duration was approximately 187 s. After excluding the rise time from the source duration, the northward rupture velocity was approximately 2.02 km/s, faster than the southward rupture velocity (1.74 km/s). On average, the rupture velocity derived from this study was slower than that estimated from finite-fault inversion; however, several historical earthquakes in the Chile region also showed slow rupture velocity when using low-frequency signals, as surface waves do. Two earlier studies through global-positioning-system data analysis showed that the static stress drop of 50–70 bars for the 2010 Chile earthquake was higher than that for subduction-zone earthquakes. Hence, a remarkable feature was that the 2010 Chile earthquake had a slow rupture velocity and a high static stress drop, which suggested an inverse relationship between rupture velocity and static stress drop.Graphical abstract.
Highlights
On February 27, 2010, the megathrust Chile earthquake (Mw 8.8) occurred near the coast of Maule in central Chile (Fig. 1)
The rupture characteristics of the 2010 Chile earthquake were mainly inferred using source rupture models inverted from P-waves and global positioning system (GPS) data
The apparent source duration varying with station azimuth indicated preliminarily the rupture feature of the 2010 Chile earthquake—not a unilateral faulting but a bilateral faulting [ refer to Figure 3 of Hwang (2014)]
Summary
On February 27, 2010, the megathrust Chile earthquake (Mw 8.8) occurred near the coast of Maule in central Chile (Fig. 1). The earthquake generated a large rupture and caused severe damage along the coast and in nearby regions. Large earthquakes occurred frequently in the Chile region, where the Nazca plate subducts beneath the South American plate with a relative moving velocity of ~6.5 cm/year (Contreras-Reyes and Carrizo 2011). The most well-known event is the 1960 Mw 9.5 Chile earthquake, the largest event observed using modern seismic instruments. In the central and southern areas of Chile (35°S–37°S), no large events occurred during 1835–2010; the region was regarded as a zone with seismic gap (Ruegg et al 2009; Moreno et al 2010, 2012). In the central and southern areas of Chile (35°S–37°S), no large events occurred during 1835–2010; the region was regarded as a zone with seismic gap (Ruegg et al 2009; Moreno et al 2010, 2012). Moreno et al (2010)
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