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David Carver

Publications and source records attributed to David Carver.

5 recordsLinked to original sources
USGS2012

Site response across downtown Santa Cruz, California

Some buildings in Santa Cruz, California, particularly those in the downtown section which is built on a flood plain, were severely damaged by the 17 October 1989 Loma Prieta Earthquake. During an aftershock study conducted in the fortnight following the mainshock, an array of seismographs was deployed across downtown to study the site response of the flood plain. Analyses of the records of eight aftershocks reveal that ground motions of the flood plain are amplified relative to those of crystalline rock sites by factors of 4–8 in the frequency band 2–8 Hz. Both resonance in the whole sedimentary column which overlies the crystalline basement and resonance/broad-band amplification in the low-velocity alluvium of the flood plain contribute to this site response.

California↗
USGS2009

Sedimentary basin effects in Seattle, Washington: Ground-motion observations and 3D simulations

Seismograms of local earthquakes recorded in Seattle exhibit surface waves in the Seattle basin and basin-edge focusing of S waves. Spectral ratios of Swaves and later arrivals at 1 Hz for stiff-soil sites in the Seattle basin show a dependence on the direction to the earthquake, with earthquakes to the south and southwest producing higher average amplification. Earthquakes to the southwest typically produce larger basin surface waves relative to S waves than earthquakes to the north and northwest, probably because of the velocity contrast across the Seattle fault along the southern margin of the Seattle basin. S to P conversions are observed for some events and are likely converted at the bottom of the Seattle basin. We model five earthquakes, including the M 6.8 Nisqually earthquake, using 3D finite-difference simulations accurate up to 1 Hz. The simulations reproduce the observed dependence of amplification on the direction to the earthquake. The simulations generally match the timing and character of basin surface waves observed for many events. The 3D simulation for the Nisqually earth-quake produces focusing of S waves along the southern margin of the Seattle basin near the area in west Seattle that experienced increased chimney damage from the earthquake, similar to the results of the higher-frequency 2D simulation reported by Stephenson et al. (2006). Waveforms from the 3D simulations show reasonable agreement with the data at low frequencies (0.2-0.4 Hz) for the Nisqually earthquake and an M 4.8 deep earthquake west of Seattle.

Bulletin of the Seismological Society of America↗
USGS2001

Configuration of the Seattle Urban Seismic Array for the February 28, 2001, M6.8, Nisqually earthquake and its aftershocks

This is a description of the configuration of the Seattle Urban Seismic Array (click on thumbnail map to see full size map) at the time of the Nisqually earthquake and its aftershocks (from April 28 through March 3, 2001). The array is operated by the Geologic Hazards Team of the U. S Geological Survey. It has been recording small local earthquakes since its initial installation immediately after the Duvall earthquake in May 1996. Since then, we have been able to convert the array to all Kinemetrics K2s after retiring the aging DR-200s in June of 1998. The array stations have been moved around to suit our research interests. We had 26 instruments in urban Seattle at the time of the Nisqually earthquake. The primary research goal of the array is to record earthquake ground motion at sites scattered around the city that represent the major types of surficial geologic materials found in the city. With this information we plan to draw seismic hazard maps that will show the expected variability of ground shaking throughout the city. Our strategy to achieve our goal includes: 1) sampling ground motion at sites that represent the major geologic materials including man-made fill and alluvial surficial materials, 2) recording high-resolution ground motions from a tripartite array (SDN, SDS, and SDW) with about 200 meter spacing located on man-made fill in the SoDo (South of Downtown) industrial district, 3) recording ground motion in areas with man-made fill and alluvial surficial materials which have a high potential for liquifaction, 4) sampling ground motion at two sites on Capitol Hill (THO, and SEU) that are located near drill holes that have been logged for seismic velocity, 5) Providing long-term continuity at a few sites for comparison and reference, especially SEW and ALK, which are located on Tertiary bedrock. 6) recording ground motion at sites with similar surficial geology both inside and outside the Seattle Basin The configuration of the array is summarized in the accompanying table which is further described below.

Washington↗
USGS1981

Aftershocks of the June 20, 1978, Greece earthquake: A multimode faulting sequence

A 10-station portable seismograph network was deployed in northern Greece to study aftershocks of the magnitude (m b ) 6.4 earthquake of June 20, 1978. The main shock occurred (in a graben) about 25 km northeast of the city of Thessaloniki and caused an east-west zone of surface rupturing 14 km long that splayed to 7 km wide at the west end. The hypocenters for 116 aftershocks in the magnitude range from 2.5 to 4.5 were determined. The epicenters for these events cover an area 30 km (east-west) by 18 km (north-south), and focal depths ranges from 4 to 12 km. Most of the aftershocks in the east half of the aftershock zone are north of the surface rupture and north of the graben. Those in the west half are located within the boundaries of the graben. Composite focalmechanism solutions for selected aftershocks indicate reactivation of geologically mapped normal faults in the area. Also, strike-slip and dip-slip faults that splay off the western end of the zone of surface ruptures may have been activated. The epicenters for four large (M ≯ 4.8) foreshocks and the main shock were relocated using the method of joint epicenter determination. Collectively, those five epicenters form an arcuate pattern convex southward, that is north of and 5 km distant from the surface rupturing. The 5-km separation, along with a focal depth of 8 km (average aftershock depth) or 16 km (NEIS main-shock depth), implies that the fault plane dips northward 58° or 73°, respectively. A preferred nodal-plane dip of 36° was determined by B.C. Papazachos and his colleagues in 1979 from a focal-mechanism solution for the main shock. If this dip is valid for the causal fault and that fault projects to the zone of surface rupturing, a decrease of dip with depth is required.

Tectonophysics↗