The dynamics of oceanic transform faults : constraints from geophysical, geochemical, and geodynamical modeling
The dynamics of oceanic transform faults : constraints from geophysical, geochemical, and geodynamical modeling
Date
2008-06
Authors
Gregg, Patricia M.
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Location
East Pacific Rise
DOI
10.1575/1912/2322
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Keywords
Geological modeling
Earthquake magnitude
Earthquake magnitude
Abstract
Segmentation and crustal accretion at oceanic transform fault systems are
investigated through a combination of geophysical data analysis and geodynamical and
geochemical modeling. Chapter 1 examines the effect of fault segmentation on the
maximum predicted earthquake magnitude of an oceanic transform fault system. Results
of thermal modeling suggest that fault segmentation by intra-transform spreading centers
(ITSC) drastically reduces the available brittle area of a transform fault and thus limits
the available earthquake rupture area. Coulomb stress models suggest that long ITSCs
will prohibit static stress interaction between segments of a transform system and further
limit the maximum possible magnitude of a given transform fault earthquake. In Chapter
2, gravity anomalies from a global set of oceanic transform fault systems are investigated.
Surprisingly, negative residual mantle Bouguer gravity anomalies are found within fastslipping
transform fault domains. These gravity observations suggest a mass deficit
within fast-slipping transform faults, which may result from porosity variations, mantle
serpentinization, and/or crustal thickness variations. Two-dimensional forward modeling
and the correlation of the negative gravity anomalies to bathymetric highs indicate crustal
thickness excesses in these locations. Finally, in Chapter 3, mantle thermal and melting
models for a visco-plastic rheology are developed to investigate the process of mantle
melting and crustal accretion at ITSCs within segmented transform faults, and are applied
to the Siqueiros transform fault system. Models in which melt migrates into the
transform fault domain from a large region of the mantle best explain the gravity-derived
crustal thickness variations observed at the Siqueiros transform. Furthermore, a mantle
potential temperature of 1350ºC and fractional crystallization at depths of 9 – 15.5 km
best explain the major element composition variation observed at the Siqueiros transform.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2008
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Citation
Gregg, P. M. (2008). The dynamics of oceanic transform faults : constraints from geophysical, geochemical, and geodynamical modeling [Doctoral thesis, Massachusetts Institute of Technology and Woods Hole Oceanographic Institution]. Woods Hole Open Access Server. https://doi.org/10.1575/1912/2322