Proceedings of Workshop XIV: earthquake hazards of the Puget Sound region, Washington

Crosson, Robert S.; Jacobson, Muriel L.

doi:10.3133/ofr8319

Cited by 12 publications

(2 citation statements)

References 59 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Their distribution shows no preference for either strike‐slip or thrust mechanisms, indicating an approximately uniaxial stress field with σ 1 > σ 2 ≈ σ 3 at that depth range. Very similar distributions have been found in general seismicity studies in the Pacific Northwest (Crosson 1972, 1983; Ma et al . 1991; Wang et al .…”

Section: Stress‐field Considerationssupporting

confidence: 85%

“…Assuming a pervasively fractured crust, the average directions of pressure ( P ) and tension ( T ) axes, averaged over a large number of earthquakes, are expected to approximate the directions of the principal stresses σ 1 (maximum) and σ 3 (minimum), respectively. Background seismicity in the Pacific Northwest appears to occur for most part under a NS compressional stress field (Crosson 1972, 1983; Ma et al . 1991).…”

Section: Stress‐field Considerationsmentioning

confidence: 99%

See 1 more Smart Citation

New techniques for the analysis of earthquake sources from local array data with an application to the 1993 Scotts Mills, Oregon, aftershock sequence

Schurr

Nábělek

1999

Geophysical Journal International

View full text Add to dashboard Cite

We analysed aftershocks recorded by a temporary digital seismic network following the moderate Mw = 5.5 1993, Scotts Mills, Oregon, earthquake. A technique to retrieve source moment tensors from local waveforms was developed, tested, and applied to 41 small earthquakes (Mw ranging from 1.6 to 3.2). The derived focal mechanisms, although well resolved, are highly variable and do not share a common nodal plane. In contrast, the majority of the events, relocated with a joint hypocentre determination algorithm, collapse to a well‐focused plane. The incompatibility of the nodal planes of most events with the plane defined by their locations suggests that the aftershocks did not occur on the fault plane, but tightly around it, outlining the rupture area rather than defining it. Furthermore, the moment tensors reveal stable P‐axes, whereas T ‐axes plunges are highly dispersed. We detect a rotation of average T ‐axis plunge with depth, indicating a change from shallower, predominantly dip‐slip mechanisms to deeper strike‐slip mechanisms. These characteristics are difficult to explain by remnant stress concentrations on the main‐shock rupture plane or asperity‐ and barrier‐type models. We suggest that the aftershocks occurred under the ambient regional stress, triggered by a sudden weakening of the region surrounding the main‐shock slip, rather than from a shear stress increase due to the main shock.

show abstract

Section: Stress‐field Considerationssupporting

confidence: 85%

Section: Stress‐field Considerationsmentioning

confidence: 99%

New techniques for the analysis of earthquake sources from local array data with an application to the 1993 Scotts Mills, Oregon, aftershock sequence

Schurr

Nábělek

1999

Geophysical Journal International

View full text Add to dashboard Cite

show abstract

P-waveform analysis for local subduction geometry south of Puget Sound, Washington

Lapp

Owens

Crosson

1990

PAGEOPH

View full text Add to dashboard Cite

Strain accumulation in western Washington

Savage¹,

Lisowski²,

Prescott³

1991

J. Geophys. Res.

View full text Add to dashboard Cite

The Juan de Fuca plate is subducted beneath the North American plate off the coast of Washington at a rate of about 40 mm/yr N68°E. The average principal strain rates (extension reckoned positive) measured in northwestern Washington are as follows: Olympic peninsula 25 km south of Port Angeles from 1982 through 1990, trueε˙1=0.011±0.027 μstrain/yr N31°E±6.6° and trueε˙2=−0.092±0.028 μstrain/yr N59°W±6.6° and near Seattle from 1972 through 1985, ε˙1=0.027±0.019 μstrain/yr N22°E±6.4° and trueε˙2=‐0.036±0.013 μstrain/yr N68°W±6.4° . Both strain measurements are consistent with uniaxial contraction in the direction of plate convergence. Uplift rates inferred from tide gage recordings are about 4 mm/yr on the Pacific coast and near 0 mm/yr farther inland near Seattle. These deformation rates are consistent with a model of the Cascadia subduction zone in which the plate interface beneath the continental slope and outer continental shelf is locked but free to slip farther landward. The limited downdip extent of the locked segment of the plate interface is consistent with a shallow depth (∼20 km) of the isotherm (∼450°C) that defines the brittle‐ductile transition. Small thrust events diagnostic of seismic subduction should then occur only offshore and at shallow depths. The principal strain rates measured from 1972 through 1983 in the back arc region near Richland, Washington, are trueε˙1=‐0.016±0.013 μstrain/yr N03°W±34° and trueε˙2=‐0.024±0.013 μstrain/yr N87°E±34° .

show abstract

Proceedings of Workshop XIV: earthquake hazards of the Puget Sound region, Washington

Cited by 12 publications

References 59 publications

New techniques for the analysis of earthquake sources from local array data with an application to the 1993 Scotts Mills, Oregon, aftershock sequence

New techniques for the analysis of earthquake sources from local array data with an application to the 1993 Scotts Mills, Oregon, aftershock sequence

P-waveform analysis for local subduction geometry south of Puget Sound, Washington

Strain accumulation in western Washington

Contact Info

Product

Resources

About