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Re: Fault Maps

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In a message dated 10/9/2000 4:48:27 PM Pacific Daylight Time, 
Gerard_Madden(--nospam--at) writes:

> This seems ridiculous to me that there can be such a discrepancy. Has anyone
> else experienced anything similar to this? Perhaps someone with a Geotech
> background could explain this huge difference in the location of a known
> fault.

It is my understanding that the Hayward SW extension on the ICBO / CDMG maps 
is the classic Hayward Fault shown on the AP map.  They should coincide;  BUT 
 the designation of the classic Hayward fault trace in this area as shown on 
the AP map has been downgraded to a Type B fault based on the amount of creep 
present in this area.

What is new is the ICBO/CDMG maps now claiming that the Mission Fault is now 
the Hayward fault south and is a Type A fault.  This sounds like the source 
of your confusion since the same labels are being used for two very different 
fault locations. 

The State Geologist has not placed the Mission fault and the Warm Springs 
fault on the Alquist Priolo map because there is no physical evidence to show 
fault surface rupture hazard at the time the map was prepared.  This does not 
mean there is not shaking hazards. The State Map is intended on show surface 
fault rupture per the Alquist Priolo Act  (Ref: ).  It will be updated 
with the new State Seismic Hazard Maps which CDMG advises will show these 
fault traces.  Maps for Fremont are not available yet.  The State has not 
released a schedule for when maps covering Fremont will be released.  For 
more information,  check their website at:

The new 1997 UBC (Uniform Building Code) ICBO fault maps prepared by CDMG 
used for structural design show the Mission fault as the Hayward South fault, 
a Class A fault,  ( as 
a step-over feature between the Calaveras fault and the Hayward fault.  It is 
my understanding the Mission and Warm Spring fault traces show seismic 
activity,  but no Holocene era surface rupture.  This determination by the 
State Division of Mines and Geology has implications for new construction or 
alterations. Locations on the map are approximate and based on research and 
seismographic recordings on the Mission and Warm Springs fault.  

Ron Fong
City of Fremont