 Frank Groffie, PG, CEG Geology consulting Clarity, communication, closure. Contact us |
| About |
| Fault investigation |
| Landslide investigation |
| Rock-slope
analysis |
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Seismic hazard analysis |
| Site characterization |
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General geosupport |
Seismic hazards analysis
Seismic-hazards analysis involves quantifying potential shaking from future earthquakes in minute detail. This
sort of analysis is called probabilistic. It’s risk analysis. It brings together findings from geologists in trenches,
seismologists, soil samples from the site, and ordinary how-far-away-are-those-faults geometry. Software is
required. We like using EZ-FriskTM software by Risk Engineering, Inc. Below are just a few examples of our work.
Elementary schools
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Groffie1 has evaluated seismic hazards and geologic conditions at several elementary schools in the Bay area
and Santa Cruz area. Generally, we analyze a site using subsurface data (drilling), regional geology data, and
software aids, but additional techniques may come into play. We probabilistically develop design-level potential
seismic acceleration values. Occasionally, special issues are involved,
including potential liquefaction. At two sites, we evaluated the
potential for tsunami impacts. At another, we evaluated the potential
hazard posed by an upstream water reservoir facility.
Hospitals, San Francisco Bay Area
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Groffie1 has evaluated seismic hazards and geologic conditions at several hospitals in the Bay area. Generally,
we analyze a site using subsurface data (drilling), regional geology data, and software aids, but additional tech-
niques may be used. We probabilistically develop design-level potential seismic acceleration values. Occasion-
ally, special issues are involved, including potential liquefaction. At one site, we evaluated the presence of
low-density sand and a nearby lagoon. Another site received our analysis of a special issue: the level of shak-
ing the buildings experienced during the 1989 Loma Prieta earthquake, centered in Santa Cruz County.
Los Altos Hills earthquake effects study
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The Mw=6.9 Loma Prieta earthquake of 1989
wascentered on the San Andreas fault in the Santa
Cruz mountains. Urbanized areas of Santa Cruz,
Watsonville, San Francisco, and Oakland were
especially hard hit in terms of structural damage
and deaths. Although the fault rupture itself
didn’t extend up to the ground surface, curious
ground extensions and shortenings and much
building damage were observed in Los Altos Hills
and nearby areas.
The County of Santa Clara commissioned us to
study the pattern of residential damage and
ground effects in the unincorporated area of
county near Los Altos Hills. Frank Groffie2 pre-
pared a report summarizing the effects on
buildings and documenting cracking in roadways and freeway structures. Groffie developed possible explanations
for the concentrated seismic effects, including focusing of seismic energy from depth up to the ground surface
through and between the local fault zones (Berrocal and Monte Vista-Shannon), topographic effects, and
possible minor transient movement on weak discontinuities. Recommendations were adopted for rebuilding
residences on the most-affected building sites and for future construction in fault zones.
1. While engaged to corporate firms, client legal relationships with those firms, some since absorbed into other corporate entities.
Relevant technical documents on file with applicable public agencies.
2. As employee of Terratech Inc., client legal relationship with that firm, since absorbed into other corporate entities. Report may
be available for viewing or purchase by the public at Santa Clara County Department of Planning and Development.
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Frank Groffie, PG, CEG, MSc, is Professional Geologist 4930 and Certified Engineering Geologist 1539, in good standing since initiation in 1989, with the State of California Board of Professional Engineers, Land Surveyors, and Geologists |
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| Web page last modified October 25, 2012 | ||||||