Wide-angle seismic recordings from the 1998 Seismic Hazards Investigation of Puget Sound (SHIPS), western Washington and British Columbia

Brocher, Thomas M.; Parsons, Tom; Creager, K. C.; Crosson, Robert S.; Symons, Neill P.; Spence, G. D.; Zelt, B. C.; Hammer, Philip T. C.; Hyndman, R. D.; Mosher, D.; Tréhu, Anne M.; Miller, Kate C.; Brink, U. S. Ten; Fisher, Michael A.; Pratt, Thomas L.; Álvarez, M.; Beaudoin, B. C.; Louden, K. E.; Weaver, Craig S.

doi:10.3133/ofr99314

Cited by 21 publications

(30 citation statements)

References 27 publications

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“…Since 1980, numerous seismic reflection‐refraction experiments have been conducted across the margin of Oregon, Washington, and British Columbia to explore the complex velocity and tectonic structure of the Cascadia convergent margin [ Spence et al , 1985; Green et al , 1986; Taber and Lewis , 1986; Clowes et al , 1987; Calvert and Clowes , 1990, 1991; Hyndman et al , 1990; Tréhu et al , 1994; Calvert , 1996; Miller et al , 1997; Flueh et al , 1998; Parsons et al , 1998, 1999; Gerdom et al , 2001]. During the Seismic Hazards Investigations in Puget Sound (SHIPS) experiment, conducted in March 1998, onshore‐offshore wide‐angle data and multichannel reflection data were collected in northwestern Washington State and southwestern British Columbia [ Brocher et al , 1999; Fisher et al , 1999]. The objectives were (1) to define the geometry of deep structures that control earthquake occurrence, including the megathrust fault that produces great earthquakes, (2) to provide detailed controls on seismic velocity crustal structure and on crustal faults, and (3) to define sedimentary basins that may affect strong motions during earthquakes.…”

Section: Introductionmentioning

confidence: 99%

Crustal structure beneath the Strait of Juan de Fuca and southern Vancouver Island from seismic and gravity analyses

et al. 2003

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[1] Wide-angle and vertical incidence seismic data from Seismic Hazards Investigations in Puget Sound (SHIPS), gravity modeling, and seismicity are used to derive twodimensional crustal models beneath the Strait of Juan de Fuca. The Eocene volcanic Crescent-Siletz terrane is significantly thicker than previously recognized and extends from near the surface to depths of 22 km or greater. For the northern strait, a weak midcrustal reflector, dipping east from 12-to 22-km depth, is inferred from wide-angle reflections. A stronger deeper reflector, dipping eastward from 23-to 36-km depth, is associated with the top of ''reflector band E,'' a zone of high reflectivity on coincident Multichannel Seismic (MCS) data, interpreted as a shear zone. A high-velocity zone (7.60 ± 0.2 km s À1 ) between these reflectors is interpreted as a localized slice of mantle accreted with the overlying Crescent-Siletz terrane. For the southern strait, no deep high-velocity layer is observed and the E-band reflectivity is weaker than to the north. A strong deep reflector, interpreted as the oceanic Moho dips eastward from 35 to 42 km. Seismicity within the subducting slab occurs mainly above the inferred oceanic Moho. Gravity modeling, constrained by the wide-angle seismic models and seismicity, is consistent with the inferred large thickness of Crescent-Siletz and high-density rocks (3030 kg m À3 ) in the lower crust.

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Section: Introductionmentioning

confidence: 99%

Crustal structure beneath the Strait of Juan de Fuca and southern Vancouver Island from seismic and gravity analyses

et al. 2003

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“…The 06 instruments were used at noisier and more accessible sites within the city of Seattle, under the assumption that the dynamic range was less important because only the largest events would be recorded at these noisier sites. PASSCAL (1991) and Brocher et al (1999) describe the REF TEK instruments. All instruments were programmed to record three channels continuously at 50 samples/sec during the duration of the experiment.…”

Section: Seismograph Deployment and Maintenancementioning

confidence: 99%

“…During the 1998 "wet" SHIPS project, airgun shots behind the University of Washington's research vessel Thomas G. Thompson were recorded by a marine multichannel system and by 250 land-based seismic recorders Brocher et al, 1999). The 1999 "dry" SHIPS study was a refraction experiment in which 1008 land seismometers were placed along an east-west profile across the Seattle basin to record 38 underground detonations (Brocher et al, 2000a;Brocher et al, 2000b;Brocher et al, 2001b).…”

Section: Introductionmentioning

confidence: 99%

Earthquake recordings from the 2002 Seattle Seismic Hazard Investigation of Puget Sound (SHIPS), Washington state

Pratt¹,

Meagher²,

Brocher³

et al. 2003

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“…Given the small volume of the CCGS Tully airgun, most of recorders were deployed along the Strait of Georgia within 10 km of the planned ship tracks (Figure 1). Thirteen of the sites used for RefTek stations represent reoccupations of 1998 SHIPS sites (Brocher et al, 1999) (Appendix 3). The other sites selected were chosen to increase the density of SHIPS wide-angle recordings to permit the inversion for higher-resolution tomography velocity models in the southern Georgia basin.…”

Section: Wide-angle Recordingmentioning

confidence: 99%

“…The median uncertainty in elevation is 17 m (Appendix 4). To the elevations provided by these GPS receivers we added 19 m, the same correction applied by Brocher et al (1999).…”

Section: Station Locations and Elevationsmentioning

confidence: 99%

Wide-angle seismic recording from the 2002 Georgia Basin Geohazards Initiative, northwestern Washington and British Columbia

Brocher¹,

Pratt²,

Spence³

et al. 2003

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This report describes the acquisition and processing of shallow-crustal wide-angle seismicreflection and refraction data obtained during a collaborative study in the Georgia Strait, western Washington and southwestern British Columbia. The study, the 2002 Georgia Strait Geohazards Initiative, was conducted in May 2002 by the Pacific Geoscience Centre, the U.S. Geological Survey, and the University of Victoria. The wide-angle recordings were designed to image shallow crustal faults and Cenozoic sedimentary basins crossing the International Border in southern Georgia basin and to add to existing wide-angle recordings there made during the 1998 SHIPS experiment. We recorded, at wide-angle, 800 km of shallow penetration multichannel seismic-reflection profiles acquired by the Canadian Coast Guard Ship (CCGS) Tully using an air gun with a volume of 1.967 liters (120 cu. in.). Prior to this reflection survey, we deployed 48 Refteks onshore to record the airgun signals at wide offsets. Three components of an oriented, 4.5 Hz seismometer were digitally recorded at all stations. Nearly 160,300 individual air gun shots were recorded along 180 short seismic reflection lines. In this report, we illustrate the wide-angle profiles acquired using the CCGS Tully, describe the land recording of the air gun signals, and summarize the processing of the land recorder data into common-receiver gathers. We also describe the format and content of the archival tapes containing the SEGY-formated, common-receiver gathers for the Reftek data. Data quality is variable but the experiment provided useful data from 42 of the 48 stations deployed. Three-fourths of all stations yielded useful first-arrivals to source-receiver offsets beyond 10 km: the average maximum source-receiver offset for first arrivals was 17 km. Six stations yielded no useful data and useful firstarrivals were limited to offsets less than 10 km at five stations. We separately archived our recordings of 86 local and regional earthquakes ranging in magnitude from 0.2 to 4.3 and 16 teleseisms ranging in magnitude 5.5 to 6.5. CONTENTS

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Wide-angle seismic recordings from the 1998 Seismic Hazards Investigation of Puget Sound (SHIPS), western Washington and British Columbia

Cited by 21 publications

References 27 publications

Crustal structure beneath the Strait of Juan de Fuca and southern Vancouver Island from seismic and gravity analyses

Crustal structure beneath the Strait of Juan de Fuca and southern Vancouver Island from seismic and gravity analyses

Earthquake recordings from the 2002 Seattle Seismic Hazard Investigation of Puget Sound (SHIPS), Washington state

Wide-angle seismic recording from the 2002 Georgia Basin Geohazards Initiative, northwestern Washington and British Columbia

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