Intensity distribution and isoseismal maps for the Nisqually, Washington, earthquake of 28 February 2001

Self Cite

100

We analyzed the regional dependence of ground motion to intensity conversion equations and derived a new global relationship to improve ground motion and intensity estimates for earthquake hazard applications, including those related to the ShakeMap system. For this purpose, we merged several databases collected by other authors in different geographical regions to highlight any systematic regional effects in the relationship between macroseismic intensities and both peak ground velocity and peak ground acceleration. Our database contains macroseismic intensities derived from expert assignments or from the "Did You Feel It?" database, paired with peak ground motions (PGM) from seismic stations. We constrain our intensity-ground-motion pairs to those with a maximum 2 km separation. For each region, we derived invertible relationships between intensities and ground motion using an orthogonal regression. We also derived a global relationship to quantify the regional differences. We investigated the dependence of intensity on predictor variables such as PGM, magnitude, and hypocentral distance. Our analyses indicate that PGM is the most robust predictor variable of intensity. Within one standard deviation, our regional and global results are in agreement with the relations of Worden et al. (2012) for California, Faenza and Michelini (2010) for Italy, Tselentis and Danciu (2008) for Greece, and Atkinson and Kaka (2007) for central-eastern United States. The earthquakes in the study ranged in magnitude from 2.5 to 7.3, and the distances ranged from less than a kilometer to about 200 km from the epicenter.

Section: Time Consistencysupporting

confidence: 85%

Ground Motion to Intensity Conversion Equations (GMICEs): A Global Relationship and Evaluation of Regional Dependency

Caprio¹,

Tarigan²,

Worden³

et al. 2015

Self Cite

100

“…Location of the mapped strands (dashed) and deformation front (solid) of the Seattle fault from Blakely et al (2002). (b) Contoured Modified Mercalli intensities from community damage reports (Dewey et al, 2002) over the same area as for Figure 3a. MMI values are compiled by zip code and displayed at the geometric center of each zip-code area, independent of actual damage locations.…”

Section: The Nisqually Earthquake and Its Geologic Settingmentioning

confidence: 99%

“…After the earthquake, we rapidly surveyed chimney-damage patterns in West Seattle and other similar neighborhoods in the greater Seattle area. Our objective was to compare the observed damage patterns with the measured ground accelerations for the 2001 earthquake, to compare (Dewey et al, 2002); strong-motion instrument sites plotted from data compiled in Table 1. our rapid surveys with damage reported to disaster-relief agencies by homeowners, to compare our results with 1965 damage in West Seattle, and to seek possible correlations between repeated chimney damage and geologic structure along the southern margin of the Seattle basin. We focused on peak ground accelerations (PGAs) for reasons of simplicity and data availability, although more sophisticated analyses using spectral values might have produced even stronger correlations.…”

Section: Introductionmentioning

confidence: 99%

Chimney Damage in the Greater Seattle Area from the Nisqually Earthquake of 28 February 2001

Booth¹,

Wells²,

Givler³

2004

Unreinforced brick chimneys in the greater Seattle area were damaged repeatedly in the Benioff zone earthquakes of 1949, 1965, and 2001. A survey of visible chimney damage after the 28 February 2001 Nisqually earthquake evaluated approximately 60,000 chimneys through block-by-block coverage of about 50 km 2 , identifying a total of 1556 damaged chimneys. Chimney damage was strongly clustered in certain areas, in particular in the neighborhood of West Seattle where prior damage was also noted and evaluated after the 1965 earthquake. Our results showed that damage produced by the 2001 earthquake did not obviously correspond to distance from the earthquake epicenter, soft soils, topography, or slope orientation. Chimney damage correlates well to instrumented strong-motion measurements and compiled resident-reported ground-shaking intensities, but it offers much finer spatial resolution than these other data sources. In general, most areas of greatest chimney damage coincide with best estimated locations of strands of the Seattle fault zone. The edge of that zone also coincides with areas where chimney damage dropped abruptly over only one or two blocks' distance. The association between shaking intensity and fault-zone structure suggests that abrupt changes in the depth to bedrock, edge effects at the margin of the Seattle basin, or localized trapping of seismic waves in the Seattle fault zone may be significant contributory factors in the distribution of chimney damage.

“…This earthquake, the largest generated by the Cascadia subduction zone (CSZ) in more than 50 years, caused nearly $2 billion dollars in damage in Washington State and was felt over 350,000 km 2 (Dewey et al, 2002). Damage was relatively modest for an earthquake of this size in an urban area because it occurred at 52 km depth within the subducting Juan de Fuca (JdF) plate.…”

Section: Introductionmentioning

confidence: 98%

Comparing Intensity Variation of the 2001 Nisqually Earthquake with Geology in Victoria, British Columbia

Molnar

Cassidy

Dosso

2004

This article compares the variation in observed intensity of the 2001 M W 6.8 Nisqually, Washington, earthquake in Victoria, British Columbia (150 km from the epicenter), with amplification hazard predictions based on the average shearwave velocity of geologic units. Modified Mercalli intensities were assigned from 750 felt reports collected by online Web submission augmented by door-to-door canvassing in regions of particular interest. An intensity map was created based on high-resolution (sub-city block) georeferencing with the Canadian postal code system. Site-specific comparisons of earthquake intensity and geology indicate significant differences in observed felt effects between high and low shear-wave velocity substrates (bedrock and glacial till versus soft clay and peat). Overall, the observed intensity map for weak levels of shaking supports the assignment of amplification hazard based on shear-wave velocities across greater Victoria.