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.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Anderson, J. G., 1979, Estimating the Seismicity from Geological Structure for Seismic-Risk Studies, Bull. Seism. Soc. Am. 69, 135–158.
Aydin, A. and Nur, A., 1982, Evolution of Pull-Apart Basins and their Scale Independence, Tectonics 1, 91–105.
Barka, A. A. and Kadinsky-Cade, K., 1988, Strike-Slip Fault Geometry in Turkey and its Influence on Earthquake Activity, Tectonics 7, 663–684.
Bergman, E. A. and Solomon, S. C., 1988, Transform Fault Earthquakes in the North Atlantic: Source Mechanism and Depth of Faulting, J. Geophys. Res. 93, 9027–9057.
Brune, J. N., 1968, Seismic Moment, Seismicity, and Rate of Slip Along Major Fault Zones, J. Geophys. Res. 73, 777–784.
Chandra, U., 1974, Seismicity, Earthquake Mechanisms, and Tectonics along the Western Coast of North America from 42° N to 61° N, Bull. Seism. Soc. Amer. 64, 1529–1549.
de, Charon, A., 1988, Structure and Tectonics of Cascadia Segment, Central Blanco Transform Fault Zone, M.S. thesis, Oregon State University, Corvallis, Oregon, 80 pp.
Embely, R. W., 1985, A Locally Formed Deep-Ocean Canyon System along the Blanco Transform, Geo-Marine Letters 5, 99–104.
Embley, R. W., Kulm, L. D., Massoth, G., Abbott, D., Holmes, M., 1987, Morphology, Structure, and Resource Potential of the Blanco Transform Fault Zone, in School, D. W., Grantz, A., Yedder, J. G., (eds.), Geology and Resource Potential of the Continental Margin of Western North America and Adjacent Ocean Basins-Beaufort Sea to Baja, California, Amer. Assoc. Petro. Geologists, 549–561.
Gutenberg, B. and Richter, C. F., 1954, Seismicity of the Earth and Associated Phenomena, Princeton University Press, Princeton, N.J.
Johnson, S. H. and Jones, P. R., 1978, Microearthquakes Located on the Blanco Fracture Zone with Sonobuoy Arrays, J. Geophys. Res. 83, 255–261.
Karsten, J. L., Hammond, S. R., Davis, E. E., and Currie, R. G., 1986, Detailed Geomorphology and Neotectonics of the Endeavour Segment, Juan de Fuca Ridge: New Results from Seabeam Swath Mapping, Geol. Soc. Amer. Bull. 97, 213–221.
Kawasaki, I., Yasutoshi, K., Ikuko, T., and Kosugi, N., 1985, Mode of Seismic Moment Release at Transform Faults, Tectonophys. 118, 313–327.
Mann, P. M., Hempton, D. C., Bradley, D. C., and Burke, K., 1983, Development of Pull-Apart Basins, Journal of Geology 91, 529–554.
Northrop, J., 1970, Accuracy of Earthquake Epicenters on the Gorda Ridge, Bull. Seism. Soc. Amer. 60, 265–267.
Riddihough, R. P., Beck, M. E., Chase, R. L., Davis, E. E., Hyndman, R. D., Johnson, S. H., and Rogers, G. C., 1983, Geodynamics of the Juan de Fuca Plate, in R. Cabre (ed.), Geodynamics of the Eastern Pacific Region, Caribbean and Scotia Arcs, Amer. Geophys. Un., 5–21.
Scholtz, C. H., 1982, Scaling Laws for Large Earthquakes: Consequences for Physical Models, Bull. Seism. Soc. Amer. 72, 1–14.
Schwartz, D. P. and Coppersmith, K. J., 1984, Fault Behavior and Characteristic Earthquakes: Examples from the Wasatch and San Andreas Fault Zones, J. Geophys. Res. 89, 5681–5698.
Segall, P. and Pollard, D. D., 1980, Mechanics of Discontinuous Faults, J. Geophys. Res. 85, 4337–4350.
Sibson, R. H., 1986, Rupture Interaction with Fault Jogs, Geophys. Monogr. 37 (Am. Geophys. Un., Washington, D.C.) 157–167.
Spence, W., 1989, Stress Origins and Earthquake Potentials in Cascadia, J. Geophys. Res. 94, 3076–3089.
Tobin, D. G. and Sykes, L. R., 1968, Seismicity and Tectonics of the northeast Pacific Ocean, J. Geophys. Res. 3, 3821–3845.
Trehu, A. M. and Solomon, S. C., 1983, Earthquakes in the Orozco Transform Zone: Seismicity, Source Mechanisms, and Tectonics, J. Geophys. Res. 88, 8203–8225.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Dziak, R.P., Fox, C.G. & Embley, R.W. Relationship between the seismicity and geologic structure of the Blanco Transform Fault Zone. Mar Geophys Res 13, 203–208 (1991). https://doi.org/10.1007/BF00369149
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00369149