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The greater San Francisco Bay Area is recognized by Geologists
and Seismologists as one of the most active seismic regions in
the United States. Three major fault zones pass through the Bay
Area in a northwest direction which have produced approximately
12 earthquakes per century strong enough to cause structural damage.
The faults causing such earthquakes are part of the San Andreas
Fault System, a major rift in the earth's crust that extends for
at least 700 miles along western California.
The San Andreas Fault System includes the San Andreas, Hayward,
and Calaveras Fault Zones. Several smaller potentially-active
faults also occur within range-front fault systems associated
with these major fault zones. The State of California, Counties,
and Cities require Fault Investigations for proposed construction
of habitable structures within potentially active fault zones.
I can design a Fault Investigation for your project to satisfy
requirements of regulatory agencies. The investigation may include
trenching to confirm the presence or absence of faulting. The
fault exploration trench will be oriented roughly perpendicular
to the mapped fault trend in the area, extending a minimum of
50 feet beyond either end of the proposed building footprint.
The walls of the fault trench will be cleaned, closely examined,
and logged for evidence of faulting. If fault traces are encountered,
appropriate building setbacks may be recommended.
Additional trenching may be required to determine fault trends
or to find an appropriate building site, free from faulting. If
fault setbacks are not feasible for the proposed project, the
age of soils relative to fault traces may be assessed in an effort
to determine the age of faulting. If faults are determined to
be old and inactive, smaller building setbacks may be feasible.
The scope of the Fault Investigation will be designed to meet
the State, County, and City requirements for your project and
may include:
- review of geologic maps, literature, and air photos,
- site reconnaissance and mapping,
- consultation with the Reviewing Geologist,
- consultation with the project Architect and Engineer,
- excavation and logging of the fault exploration trench,
- drafting and report preparation.
The Fault Investigation will produce detailed trench logs, a site
geologic map, and cross-sections which delineate approximate boundaries
of faults and recommended building setbacks, as appropriate. |
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