ON THE SENSITIVITY OF HYDROTHERMAL AREAS TO SMALL CRUSTAL DEFORMATION: LESSONS FROM CALISTOGA GEYSER

The response of hydrothermal systems to local and distant seismicity has been noted by others, increasingly so over the last ten years. Calistoga Geyser, a hydrothermal feature in northern California, has responded to moderate and major earthquakes in the region. Here we examine the use of the geyser as a strainmeter in terms of its sensitivity and noise level in terms of its variability in the interval between eruptions. The geyser shows no observable sensitivity to Earth tides, but does show a sensitivity to atmospheric loading that is usually masked by the inherent noise level of the geyser. Changes in interval are caused by earthquakes, but there are many other changes that are the result of the geyser's internal dynamics. Calistoga Geyser is not a reliable strainmeter because of its noise level and at best is a modest indicator of crustal deformation. It is possible that its response to earthquakes represents a local alteration of permeability due to deformation rather than an elastic response.