1995 Antofagasta earthquake

Tectonic setting

Chile lies along the oblique convergent boundary between the oceanic Nazca plate and the continental South American plate. Crustal deformation is primarily accommodated by two main types of faulting: strike slip and reverse faulting subduction zone earthquakes. Reverse faulting deformation is taken up by the Peru-Chile Trench, on which this earthquake occurred. Slip rate on the fault is 68-80 mm/yr, and as a result the subduction zone is responsible for many megathrust earthquakes in the region. Some of the largest recorded earthquakes ever recorded occurred in the area, such as the 1960 Valdivia earthquake, the 1730 Valparaíso earthquake, and the 1420 Caldera earthquake. Strike slip faulting is taken up the by the Liquiñe-Ofqui Fault. It is responsible for a 7.7 earthquake as part of the aftershock sequence of the 1960 Valdivia earthquake, and potentially was involved with the main rupture as well.

Earthquake

At 1:11 local time on July 30, 1995, a large earthquake struck northern Chile. The 8.0 earthquake struck at a depth of 46 km with an epicenter near Antofagasta. The focal mechanism of this earthquake indicates thrust faulting along the subduction zone, which is consistent with other large earthquakes along the plate boundary in this region. The maximum slip was 5.4 m along a 180x70 km zone of rupture. Foreshock activity was minimal, but large aftershocks lasted a while after the mainshock, with the largest being a shallower 6.4 event with a Modified Mercalli Intensity of VII three days later. The event occurred at the edge of a known seismic gap that produced the 1877 Iquique earthquake, and research suggests that this earthquake may have put more stress on the region as well. The event is not thought to have ruptured the shallow plate interface in the region, leaving it susceptible to future large megathrust earthquakes such as the 1877 event.

Tsunami

The tsunami observed was smaller than expected, however this may be explained by the depth of the event. Maximum run-up height was measured at 2.8 m at Antofagasta. Tide gauges at Antofagasta, Caldera, and Iqiuque recorded wave heights of 1.5 m, 0.6 m, 0.3 m respectively. 10 hours after initial rupture, tsunami waves reached French Polynesia where anomalously large run-ups of 2.5 m and crest-to-trough wave heights of 3 m were recorded. Tahiti itself recorded a small tsunami of 20 cm, while Hilo, Hawaii registered heights of 80 cm.

References

References

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