Mature Seismic Gap

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Science  05 Jul 2002:
Vol. 297, Issue 5578, pp. 15
DOI: 10.1126/science.297.5578.15c

The beautiful coastal ranges of Chile are seismically active, averaging a large-magnitude earthquake every 10 years. This activity is due to the subduction of the Nazca Plate beneath the South American Plate. The number of seismic instruments deployed in Chile is small, so it has been difficult to determine the seismic hazard and how much of the plate motion is accommodated in the crust. In particular there is a region along the coast between latitudes 35 to 37 degrees that has not experienced a subduction-zone earthquake since 1835. This region may represent a mature seismic gap that has a higher probability of a large earthquake than other regions along the subduction zone.

Ruegg et al. measured the interseismic velocity of surface locations above the subduction zone using Global Positioning System measurements. The coastal sites are moving about 40 millimeters per year relative to a stable South America. This suggests that the subduction zone is locked below the coastal sites, that strain is accumulating, and that a subduction-zone earthquake is likely. The 18 June 2002 earthquake (magnitude 6.6) at 31 degrees south near Coquimbo occurred north of the gap and may not have helped relieve strain. — LR

Geophys. Res. Lett.29, 10.1029/2001GL013438 (2002).

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