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Seismic channel waves in the accretionary prism of the Middle America Trench
Author(s) -
Shapiro N. M.,
Campillo M.,
Singh S. K.,
Pacheco J.
Publication year - 1998
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/97gl03492
Subject(s) - geology , accretionary wedge , trench , seismology , rayleigh wave , seismogram , prism , seismometer , continental shelf , seismic wave , attenuation , surface wave , subduction , tectonics , optics , oceanography , physics , chemistry , organic chemistry , layer (electronics)
A visual examination of seismograms of earthquakes located near the Middle America Trench and recorded on VBB seismographs along the Pacific coast of Mexico, when bandpass filtered between 6 and 30 s, shows the presence of two types of waves. The first is a short pulse and the second is a dispersed wavetrain. The first type of wave is quickly attenuated, while the second type propagates without significant attenuation. We applied a frequency‐time analysis to identify the nature of these waves. A comparison of period‐group velocity diagrams for signals recorded on different stations shows that the first arrival is a Rayleigh wave propagating in the continental plate, while the second one propagates along the trench in the thickened sediment wedge of the accretionary prism. We have also measured group velocities of Rayleigh wave propagating in the Cocos plate far from the coast. At periods between 15 and 20 s, the group velocities of the wave propagating along the trench are lower than the velocity of Rayleigh waves propagating in adjacent continental and oceanic plates. We conclude that the dispersed wavetrain observed near the coast is a wave trapped in a channel formed by low‐velocity sediments of the accretionary prism.