Preserving our natural resources & quality of life
GEOTHERMAL EARTHQUAKES ARE INCREASINGLY IMPACTING THE
RESIDENTS, PROPERTY & NATURAL RESOURCES OF ANDERSON SPRINGS
Updated through May 17, 2003
1. At least 8 key factors influence the impact geothermal earthquakes have on our residents & property:
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Magnitude of the earthquakes;
Frequency of the earthquakes;
Proximity to the earthquakes’ epicenter;
Proximity to the earthquakes’ hypocenter;
Directionality & nature of the earthquakes’ seismic waves;
Characteristics of the underlying faults, soils, and geology;
Design & construction of the homes and other structures; and,
Individual sensitivities & perceptions about earthquakes.
2. Based on the many factors that influence the impact of geothermal earthquakes, please note that
earthquake magnitude, though important, is only one factor. As community-wide surveys, damage
photos, and anecdotal experience of residents have effectively demonstrated, these other 7 factors have a
big effect on how earthquakes impact people and their property: the sheer frequency of these
earthquakes; their close proximity to within a couple of miles of people’s homes; their extremely shallow
depth (usually less than a mile or two deep); the nature of their seismic waves; characteristics of the soils,
faults & geology that underlie Anderson Springs (Franciscan Complex, Alluvium, and landslides); and the
design & construction of most homes (built long before earthquake codes existed or the presence of local
earthquakes warranting any special design). Also, it cannot be assumed that the residents of Anderson
Springs are any more sensitive to earthquakes than other people.
3. Given residents’ consistent, individual experiences of the human & property impacts from these
geothermal earthquakes on our community—despite equally consistent industry & County opinions
that these earthquakes aren’t a problem and such small events cannot possibly damage property—
below is a simple model that quantifies the number of likely earthquake impacts on people & property
at Anderson Springs (while many residents may not be around 24 hours a day, 7 days a week, 365 days
a year, these frequent earthquakes do still cumulatively impact their homes & properties to varying
extents with EVERY event). This model presumes cumulative impacts based on the following events:
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All earthquakes with M ≥ 1.2 from 0 to < 2 miles impact people & property at Anderson Springs;
Similarly, all earthquakes with M ≥ 1.5 from 2 to < 4 miles impact Anderson Springs;
All earthquakes with M ≥ 2.0 from 4 to < 6 miles impact Anderson Springs; and,
All earthquakes with M ≥ 2.5 from 6 to 8 miles impact Anderson Springs.
4. For January 1 through May 17, 2003, the results were as follows:
 M ≥ 1.2 from 0 to < 2 miles =194 earthquakes with 1.6 average Magnitude
 M ≥ 1.5 from 2 to < 4 miles = 62 earthquakes with 1.9 average Magnitude
 M ≥ 2.0 from 4 to < 6 miles = 21 earthquakes with 2.4 average Magnitude
 M ≥ 2.5 from 6 to 8 miles
Year-to-Date Total:
= 11 earthquakes with 2.8 average Magnitude
288 earthquakes with 1.7 average Magnitude
5. Given that by May 17th there had already been 137 days in 2003, then these 288 events can be
annualized to 767 earthquakes that will have cumulatively impacted the people & property of
Anderson Springs by the end of 2003. If one divides these 767 earthquakes by 365 days, then
an average of 2.1 earthquakes impact the people & property of Anderson Springs EVERY day!
For all of 2001, these same calculations show that there were 517 such events, resulting in an average of
1.4 earthquake impacts per day. For all of 2002, these same calculations show that there were 707 such
events, resulting in an average of 1.9 earthquake impacts per day (a 37% increase relative to 2001).
Assuming year-to-date activity continues at the same pace or greater (as happened the last 2 years), then
earthquake impacts will have increased by another 8% over 2002 (and by 48% since 2001)!
6. This simple calculation for the number of earthquake impacts on local residents and their property
corresponds to actual experiences at Anderson Springs, based upon the results of a comprehensive
Earthquake Survey recently conducted for Anderson Springs, as well as on many interviews with local
residents: Some days no earthquakes are felt, other days residents feel as many as 6 earthquakes per day; an
average of 2 earthquakes per day impacting residents & their property is highly likely (though perceptions do
vary depending on one’s property location and proximity to the geothermal injection/production zones).
7. Lake County and the geothermal operators increasingly risk substantial exposure & liability for possible
loss of life, health problems/injuries, environmental degradation, and property damage—including the
eventuality of seismic retrofitting or inverse condemnation for many properties in the Anderson Springs
and/or Cobb areas, potentially costing hundreds of millions of dollars.
8. We want to reiterate the urgency of establishing an independent baseline and expanded monitoring of the
current situation affecting Anderson Springs (including our structures), starting in the 6 months before
Santa Rosa’s project more than doubles injection volumes at The Geysers. We ask for a commitment
from the County, the geothermal operators, and outside agencies with responsibility for such matters to
work with our organization over the next couple of months to define, fund, and launch a comprehensive,
independent Baseline Assessment & Monitoring Program.
Respectfully submitted,
Jeffrey D. Gospe, President
Anderson Springs Community Alliance