Double seismic zone beneath the Mariana Island arc

Journal Article · Mon Aug 10 04:00:00 EDT 1981 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB086iB08p07013· OSTI ID:5875161

Samowitz, I R; Forsyth, D W

A double zone of seismicity has been found beneath the northern Marianas in the depth range 80--120 km. The Benioff zone undergoes a pronounced bend, with radius of curvature about 200 km, before straightening and descending nearly vertically to a depth of more than 600 km. Thus this is an ideal area in which to search for evidence of stresses associated with unbending of the subducted oceanic plate. We relocated all teleseimic events from 1963 through 1975 by using a regional, composite master event technique, which significanly decreased the scatter of the hypocenters. The three events of lower seismic zone are separated from the upper zone by about 30-35 km. The true thickness of the upper seimic zone is probably 20 km or less. The limited focal mechanism data indicate that there is downdip tension in the lower zone and downdip compression in the upper zone. The seismicity patterns could be generated either by thermal stresses or by unbending a plate which was originally deformed anelastically. We show that an elastic-perfectly plastic model of the rheology of the plate can account for the seperation of the two seismic zones, the focal mechanism, and the greater activity of the upper seismic zone.

• Research Organization: Department of Geological Sciences, Brown University, Providence, Rhode Island 02912
• OSTI ID: 5875161
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 86:B8; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580500* -- Oceanography-- (1980-1989)
BENDING
EARTH CRUST
EARTHQUAKE FOCI
EARTHQUAKES
FLEXURAL STRENGTH
ISLANDS
MECHANICAL PROPERTIES
OCEANIC CRUST
PACIFIC OCEAN
PLATE TECTONICS
SEA-FLOOR SPREADING
SEAS
SEISMIC EVENTS
SEISMICITY
SURFACE WATERS
TECTONICS