The Washington Regional Seismograph Network (WRSN) earthquake catalog shows more earthquakes in the day than at night, probably because some local explosions are misidentified as earthquakes. We have implemented a method to help... more
The Washington Regional Seismograph Network (WRSN) earthquake catalog shows more earthquakes in the day than at night, probably because some local explosions are misidentified as earthquakes. We have implemented a method to help discriminate likely local blasts from local earthquakes. Probable blasts are identified based on time of occurrence (year, month and hour), magnitude, location, and depth. We have defined thirteen areas in Washington and northern Oregon, with enhanced daytime activity probably due to blasts, and have developed specific time, magnitude, and depth criteria for each area to best identify probable blasts. Except in a few regions, most of the smallest, shallowest events occurring during the day in Washington and northern Oregon are probably blasts.
Research Interests: Geology and Seismology
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This article examines local myth and folklore related to earthquakes, landslides, and tsunamis in oral traditions from Cascadia (part of the northern Pacific coast of North America) and in written traditions from Japan, particularly in... more
This article examines local myth and folklore related to earthquakes, landslides, and tsunamis in oral traditions from Cascadia (part of the northern Pacific coast of North America) and in written traditions from Japan, particularly in the Edo (present-day Tokyo) region. Local folklore corresponds closely to geological evidence and geological events in at least some cases, and the symbolic language of myth and folklore can be a useful supplement to conventional geological evidence for constructing an accurate historical record of geological activity. At a deep, archetypical level, Japan, Cascadia, and many of the world's cultures appear to share similar themes in their conception of earthquakes. Although folklore from Cascadia is fragmentary, and the written record short, the evolution of Japanese earthquake folklore has been well documented over a long period of history and illustrates the interaction of folklore with dynamic social conditions.
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A comparison of seismicity at The Geysers and in the surrounding region indicates that the rate of seismicity at The Geysers is 45 times the regional rate and that clustering of events in space and time is more prevalent in the region... more
A comparison of seismicity at The Geysers and in the surrounding region indicates that the rate of seismicity at The Geysers is 45 times the regional rate and that clustering of events in space and time is more prevalent in the region area than at The Geysers. Temporally clustered seismic events that occurred at The Geysers from September 1975 through September 1976 appear linked to regional temporal clusters located at the southern end of Clear Lake. During this period, a characteristic 2- to 6-day time lapse separated temporal clusters at The Geysers from those at Clear Lake. The two areas where these correlated clusters occurred lie on either side of a presumed magma body. Correlation between clusters in the two areas disappears after September 1976. During the period of correlated seismic episodes, regional stress changes may have been transmitted between the two areas by aseismic creep.
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Research Interests: Geology and Fact Sheet
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Ludwin2001_Poster_SSA.pdf – Presented at Seismological Society of America Annual Meeting, 2001: Companion Poster to peer-reviewed article: Ludwin, R.S., R. Dennis, D. Carver, A.D. McMillan, R. Losey, J. Clague, C. Jonientz-Trisler, J. Bowechop, J. Wray, K. James, 2005, Dating the 1700 Cascadia ea...more
Companion Poster to peer-reviewed article: Ludwin, R.S., R. Dennis, D. Carver, A.D. McMillan, R. Losey, J. Clague, C. Jonientz-Trisler, J. Bowechop, J. Wray, K. James, 2005, Dating the 1700 Cascadia earthquake; Great coastal earthquakes... more
Companion Poster to peer-reviewed article: Ludwin, R.S., R. Dennis, D. Carver, A.D. McMillan, R. Losey, J. Clague, C. Jonientz-Trisler, J. Bowechop, J. Wray, K. James, 2005, Dating the 1700 Cascadia earthquake; Great coastal earthquakes in Native stories, Seismological Research Letters, V. 76, No. 2, pp.140-148.
Ludwin2003_Poster_GSA.pdf - Presented at Geological Association of America Annual Meeting, Seattle, 2003: Companion Poster to peer-reviewed article: Ludwin, R.S., C. P. Thrush, K. James, D. Buerge, C. Jonientz-Trisler, J. Rasmussen, K.... more
Ludwin2003_Poster_GSA.pdf - Presented at Geological Association of America Annual Meeting, Seattle, 2003: Companion Poster to peer-reviewed article: Ludwin, R.S., C. P. Thrush, K. James, D. Buerge, C. Jonientz-Trisler, J. Rasmussen, K. Troost, A. De Los Angeles, 2005, Serpent spirit-power stories along the Seattle Fault, Seis. Res. Lett. V. 76, No. 4, pp. 426-431.
The 1990 Pacific Northwest regional AGU meeting held September 13-14 at the University of Washington, Seattle, was attended by more than 80 people; 24 papers and 17 posters were presented. About 25 people participated in a field trip to... more
The 1990 Pacific Northwest regional AGU meeting held September 13-14 at the University of Washington, Seattle, was attended by more than 80 people; 24 papers and 17 posters were presented. About 25 people participated in a field trip to look at debris flow processes, deposits and hazards at Mount Ranier, organized by Patrick Pringle of the Washington Department of Natural Resources, Division of Geology. Published copies of the field trip guide will be available in 1991 from the Washington State DNR.Also featured at the meeting was an interdisciplinary study by the Geology, Forest Resources and Engineering departments of the University of Washington, ``Characterization and Modeling of a Hollow in the Cascades With Respect to Slope Stability.'' Slope stability is an important topic in the Pacific Northwest because of its rugged topography and the economic importance of both forestry and fisheries.
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The effects of basin shape upon strong ground motion in shallow alluvial basins is examined for a series of simple, geometric basins. The resulting psuedovelocity response spectra contour maps form the basis for the analysis of realistic... more
The effects of basin shape upon strong ground motion in shallow alluvial basins is examined for a series of simple, geometric basins. The resulting psuedovelocity response spectra contour maps form the basis for the analysis of realistic basin models to be presented in the final report.
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Many whirlpools formed during the 2004 Indian Ocean tsunami. Whirlpools were photographed by SPOT satellites and reported by observers in at least a half-dozen locales. Whirlpools have previously been reported in a number of other... more
Many whirlpools formed during the 2004 Indian Ocean tsunami. Whirlpools were photographed by SPOT satellites and reported by observers in at least a half-dozen locales. Whirlpools have previously been reported in a number of other tsunamis, and are a memorable feature of the human experience of a tsunami.
A Brief Account of the Catfish (Namazu) as a Cultural Symbol in Japan, 15th-20th Centuries
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ABSTRACT Probable effects of geothermal development on seismicity at the Geysers are shown by the spatial coherence of decreases in gravity and pressure with maximum geodetic deformation and seismic moment sum along a line through the... more
ABSTRACT Probable effects of geothermal development on seismicity at the Geysers are shown by the spatial coherence of decreases in gravity and pressure with maximum geodetic deformation and seismic moment sum along a line through the most developed area of the geothermal field. Increases in the mean number of events per day and in the magnitude of largest annual event correlate with increases in steam production. The two largest earthquakes in the steam field occurred near the two injection wells most distant from production wells, and large events (M/sub c greater than or equal to 2.5) occurred most frequently during months of peak injection. Spatial seismic clusters in proximity to injection wells have occurred soon after injection began. Preliminary data also indicate an increase in seismicity in a previously aseismic area near plant 15 following the beginning of power production at that plant in 1979.
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... magnitude Relationships. Thomas M. Brocher US Geological Survey, Menlo Park Craig S. Weaver US Geological Survey, Seattle. Ruth S. Ludwin Dept. of Earth and Space Sciences, University of Washington. INTRODUCTION. ...