RHEOLOGICAL CONTROL OF THE DEEP JULY 16, 1990 EARTHQUAKE
(CENTRAL LUZON, PHILIPPINES)
On July l6, 1990, an earthquake of magnitude Ms=7.8 occurred in the central part of Luzon island (Philippines) along a splay of the strike-slip Philippine Fault. In the rupture area, the base of the seismogenic zone as defined by aftershock distribution lies at around 25 km.
Rheological modelling based on a simple brittle-ductile transition indicates that this unusual depth may be explained by the composition of the lower crust and by a relatively low thermal gradient (~20°C/km) in the mainshock area.
It is also suggested that the juxtaposition of geological terranes with contrasting thermal gradients may favour the localization of large earthquakes along some segments of the Philippine Fault.
Society of the Philippines
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