Seismicity Structure of the Northern Chile Forearc From >100, 000 Double‐Difference Relocated Hypocenters. Issue 5 (19th May 2018)

• Record Type: Journal Article
• Authors: Sippl, C.; Schurr, B.; Asch, G.; Kummerow, J.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 5(2018)
• Page Start: 4063
• Page End: 4087
• Publication Date: 2018-05-19
• Subjects: intermediate‐depth earthquakes -- northern Chile -- seismicity -- slab hydration -- subduction zone; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1002/2017JB015384
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: In this study, we present high‐resolution seismicity images of the northern Chile subduction zone forearc. We used 8 years of continuous seismic waveform data from the Integrated Plate Boundary Observatory Chile network and auxiliary stations to produce an extensive earthquake catalog containing 101, 601 double‐difference relocated earthquake hypocenters using automatic event detection and phase picking routines. The minimum magnitude of retrieved events is <2, and the catalog is estimated to be complete at magnitudes above ∼2.8. Intraslab seismicity makes up the majority of detected earthquakes. Where the seismogenic zone of the megathrust is active, a clear separation of seismicity into three distinct planes can be observed. The uppermost plane corresponds to the plate interface, which is observed to terminate downdip at a depth of 50–55 km. The other two planes, located ∼7 and ∼26 km below the slab surface, dip at a constant angle of about 20° until they are absorbed by a 25 km thick highly active cluster of intermediate‐depth seismicity at depths of 80–120 km. Downdip of this cluster, the slab steepens and lower plate seismicity is considerably sparser, even absent in the northern part of the study area. Upper plate seismicity is also considerable, with a segment between 21 and 21.6°S standing out for featuring pervasive activity occurring all the way down to the plate interface. Here the seismicity resembles a wedge in west‐east profile view and occurs where the upper plate crust is coldest based on thermal models. Key Points: Eight years of IPOC network seismic data were harvested for microseismicity, obtained catalog features 101k events Majority of seismicity is at intermediate depths, where a usual double seismic zone grades into a highly active, 25 km thick cluster Pervasive upper plate seismicity is observed in an area around 21 degrees S, forming a wedge‐like structure extending down to the interface