Relationship between the seismicity and geologic structure of the Blanco Transform Fault Zone |
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| Authors: | Robert P Dziak Christopher G Fox Robert W Embley |
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| Institution: | (1) Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, 97365 Newport, OR, USA;(2) Cooperative Institute for Marine Resources Studies, Oregon State University Hatfield Marine Science Center, 97365 Newport, OR, USA |
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| Abstract: | Morphologic studies of an oceanic transform, the Blanco Transform Fault Zone (BTFZ), have shown it to consist of a series of extensional basins that offset the major strike-slip faults. The largest of the extensional basins, the Cascadia Depression, effectively divides the transform into a northwest segment, composed of several relatively short strike-slip faults, and a southeast segment dominated by fewer, longer faults. The regional seismicity distribution (m
b
 4.0) and frequency-magnitude relationships (b-values) of the BTFZ show that the largest magnitude events are located on the southeast segment. Furthermore, estimates of the cumulative seismic moment release and seismic moment release rate along the southeast segment are significantly greater than that of the northwest segment. These observations suggest that slip along the southeast segment is accommodated by a greater number of large magnitude earthquakes. Comparison of the seismic moment rate, derived from empirical estimates, with the seismic moment rate determined from plate motion constraints suggests a difference in the seismic coupling strength between the segments. This difference in coupling may partially explain the disparity in earthquake size distribution. However, the results appear to confirm the relation between earthquake size and fault length, observed along continental strike-slip faults, for this oceanic transform. |
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| Keywords: | Blanco Transform divergent wrench-fault earthquake b-value seismic moment fault length |
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