Physics
Scientific paper
May 1978
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1978pepi...16..318m&link_type=abstract
Physics of the Earth and Planetary Interiors, Volume 16, Issue 4, p. 318-326.
Physics
7
Scientific paper
Intraplate stresses in middle South America are not negligible. We report thrust-faulting mechanisms for five intraplate earthquakes, which indicate a dominant horizontal deviatoric compressional stress oriented in a NW-SE direction. We conclude that this state of stress is due to forces connected with spreading on the Mid Atlantic Ridge and resistive forces exerted by the Caribbean plate to the north and the Nazca plate to the west. The existence and nature of the resistive forces is inferred from earthquake mechanisms and geological evidence presented in other studies. All the available intraplate stress data for Nazca and South America indicate that both plates are under deviatoric compression generated at spreading centers. The absence of tensional earthquake focal mechanisms, particularly in the Nazca plate near the trench, suggests that the forces associated with the gravitational sinking of subducted lithosphere are locally compensated. We present a simple numerical calculation of a non-subducting plate to show how the compressional deviatoric stresses in middle South America can be used to estimate an upper bound of about 1021 P for the viscosity of the mantle.
Mendiguren Jorge A.
Richter Frank M.
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