High seismic activity occurs along the Caribbean and the North
American Plate boundary beneath the eastern part of Hispaniola. A
large number of intermediate to deep earthquakes are clustered between
the Puerto Rico Trench to the north and the Muertos Trench to the
south suggesting the possibility of concurrent subduction from both
north and south.
The body wave inversion technique was used to analyze nine
earthquakes, the largest teleseismically recorded events since the
establishment of WWSSN (World Wide Standardized Seismograph
Network) in 1963 in the geographic region between 72°W and 66°W
latitude and 16°N and 21°N longitude. Their body-wave magnitude
ranges from 5.6 to 6.1. Each event was inverted for strike, dip and slip
of the two possible fault planes, as well as for the centroid depth, the
total seismic moment and the source time function.
In order to optimize the crustal structure parameters used in the
body wave inversion method, a two-dimensional geophysical cross-section
across Hispaniola was constructed by forward modeling of
gravity and magnetics data.
The inversion results are consistent and can be divided into
groups according to the depth and the epicentral location of the events.
The shallow events, with depths of 6 to 12 km, represent crustal
deformation and show thrust mechanisms with large strike-slip
component. The intermediate depth events range from 42 to 107 km in
depth and occur to the south of eastern Hispaniola. They show clear
thrust mechanisms with a consistent dip of the compressional P-axis at
about 30° to the north and approximately north-south P-axis strike. The
deep earthquakes occur between 110 and 177 km depth, have a
steep-dipping tensional T-axis, and define another slab, possibly
originating at the Puerto Rico Trench to the north. One m[subscript b]=6.l event,
which occurred on 6/24/84, shows opposite orientations of the P- and T-axes
from the surrounding intermediate events. It is interpreted as an
interface event in the upper mantle.
The southern subduction zone is well defined and indicates that
the Muertos Trench is active, with the subducting plate dipping to the
north beneath eastern Hispaniola. At a depth of about 110 km, the
northward dipping slab collides with the almost vertical segment of the
other slab. This deep vertical slab segment, extending to at least 200 km
in depth, may be a remnant of an earlier subduction zone associated
with the Puerto Rico Trench. Alternatively, it may be connected with a
more gently dipping part of the slab towards the north or, even in some
way, with subduction from the south. / Graduation date: 1990
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29148 |
| Date | 03 November 1989 |
| Creators | Ludwig, Rainer |
| Contributors | Nabelek, John, Ness, Gordon E. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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