Descr: Large well-water level changes (>10 cm) in response to distant (>100s km) earthquakes have proven enigmatic for over 30 years [Bower and Heaton, 1978]. The redistribution of pore pressure can generate crustal deformation and perhaps even trigger seismicity [Hill, 1993]. However, the mechanism by which small cyclic stresses induce persistent pore pressure changes has remained uncertain. We propose to constrain the mechanism for coseismic water level steps by using both high-sample rate water level data and seismic data at a well-studied site in Grants Pass, OR. The transfer function from the ground velocity to the water level in the well is sensitive to the aquifer properties [Cooper, 1965]. Therefore, if we measure both the water level and the seismic ground velocity, we can measure the aquifer permeability. A preliminary study shows that we can measure permeability changes induced by seismic waves using this method. For the preliminary study, we used seismic data from the broadband Berkeley Digital Seismic Network station Yreka Blue Horn Mine (YBH) in Yreka, CA (41.732N 122.71039W). The 100 km separation between well and seismometer makes precise analysis of the phase response impossible and does not allow us to account for local site effects. We therefore request a seismometer and datalogger to install at Grants Pass next to the well (42.5N 123.37W). Since we are studying the frequency response to regional and teleseismic events, the seismometer must be broadband. The well typically has oscillatory responses to 5 teleseisms per year and produces a quasi-permanent offset once every two years. It is therefore crucial to maintain continuous monitoring over as long a time as possible. We expect to acquire a permanent seismometer in late 2002 or early 2003. We therefore request one instrument from PASSCAL to cover the site for the next year. Bower, D.R. and K.C. Heaton, Response of an aquifer near Ottawa to tidal forcing and the Alaskan earthquake of 1964, Canadian Journ. of Earth Sci., 15, 331-340, 1978. Cooper, H.H., J.D. Bredehoeft, I.S. Papdopulos and R.R. Bennett, The Response of Well-Aquifer Systems to Seismic Waves, Jour. Geophys. Res., 70, 3915-3926, 1965. Hill, D.P. et al., Seismicity Remotely Triggered by the Magnitude 7.3 Landers, California, Earthquake, Science, 260, 1617-1623, 1993.
