Geology Reports⌕ Search
Home/Archive/USGS

USGS · 70242672

Site response across downtown Santa Cruz, California

Edward Cranswick·Kenneth King·David Carver·David M. Worley·Robert Williams·Paul A. Spudich·Robert Banfill
View original source ↗Export metadata ↓

Abstract

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.

Explore related subjects

Geophysical Research LettersArticle
90° N90° S · 180° W ← longitude → 180° E
Source-reported bounding extent: 36.94645266728794° to 36.991448917195655° latitude; -122.09883583355847° to -121.87437835374348° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Edward Cranswick, Kenneth King, David Carver, David M. Worley, Robert Williams, Paul A. Spudich, Robert Banfill. 2012-12-07. Site response across downtown Santa Cruz, California. https://doi.org/10.1029/gl017i010p01793

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

Evolution of summit magma pressure during the 2018 caldera collapse at Kılauea volcano

We utilized geodetic data from the 16 May to 4 August 2018 caldera collapse sequence to refine the geometries and pressure evolution of two summit reservoirs at Kīlauea volcano: the shallower Halema‘uma‘u (HMM) and deeper South Caldera (SC) reservoirs. We modeled magma reservoirs as pressurized spheroidal cavities and constrained reservoir geometries with Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar displacements. Inverting high-rate GPS and borehole tilt time series recovered time-dependent reservoir pressure changes and caldera ring fault shear stress. During the collapse sequence, the HMM reservoir accommodated episodic, co-collapse pressure increases of 1.9 MPa (median) and a net 5.8 MPa (median) decrease. Simultaneously, the SC reservoir underwent monotonic depressurization of 6.7 MPa (median). Negligible co-collapse pressure changes in the SC reservoir imply it was not exclusively supplying magma to the eruption vent. These results provide a coherent view of magma reservoir pressure evolution during the 2018 eruption.

Hawaii↗
USGS2026

EMIT reveals elevated calcite signatures in shorelines of Lake Powell and Lake Mead exposed by drought and Colorado River management

Nearly half of Earth’s seasonal freshwater storage variability occurs in human-managed reservoirs, resulting in large areas of reservoir-bed that are episodically inundated or subaerially exposed. Here we use hyperspectral data from NASA’s Earth Surface Mineral Dust Source Investigation (EMIT) mission to map calcite mineral assemblages across exposed surfaces in two large U.S. reservoirs, Lake Mead and Lake Powell. Results show distinct patterns in the occurrence of carbonate, clay, and mica minerals. Reservoir-deposited sediments exhibited significantly higher calcite proportions than adjacent, lithologically similar, non-inundated terrestrial surfaces. These differences likely reflect hydrologically-driven calcite precipitation, wherein warm, clear, productive reservoir waters drive calcium carbonate out of solution. We also detect reductions in calcite proportions in areas of the shoreline disturbed by human recreation. EMIT's imaging capabilities enable rapid, high-resolution mineralogical inventories across vast areas where field sampling is infeasible. We find EMIT is a scalable tool for monitoring geochemical changes associated with large water level fluctuations.

Arizona, Nevada, Utah↗
USGS2026

First application of a coastal-dune model (AeoLiS) to simulate fluvial-aeolian morphodynamics

Quantifying aeolian processes is important to decision-making in river management and for optimizing strategies for ecosystem conservation, natural resource management, and recreation. We applied the AeoLiS aeolian transport model, originally developed for coastal environments, to a dryland river corridor to evaluate its ability to simulate sediment dynamics in a fluvial-aeolian system. The model reproduced spatial and temporal patterns of geomorphic change at a Grand Canyon sandbar, including aeolian dune formation, observed in field data. The model effectively captured trends in observed sediment movement in the spring and summer months. Thus, despite assuming a single grain-size, static vegetation, and not directly accounting for variable sediment supply from fluvial sources, the model performs well at capturing aeolian processes in a complex fluvial-aeolian system. AeoLiS demonstrates strong potential for dryland river applications and management, due to its flexibility and compatibility with coupled modeling frameworks.

Arizona↗