The regional subsurface structure of Long Valley (California) caldera fill from gravity and magnetotelluric data

Three‐dimensional electrical resistivity model of the hydrothermal system in Long Valley Caldera, California, from magnetotellurics

“…Electric and electromagnetic (EM) methods, specifically magnetotellurics (MT) [Chave and Jones, 2012], have been used to successfully image geothermal systems because of large contrasts between electrically conductive hydrothermal fluids and hydrothermally altered clays with surrounding resistive host rocks [e.g., Muñoz, 2014]. Multiple EM and MT studies of Long Valley Caldera have imaged the subsurface down to 5 km [Hermance et al, 1984[Hermance et al, , 1988Park and Torres-Verdin, 1988;Wannamaker et al, 1991;Sorey et al, 1991;…”

Volcanology

“…The strongest support for magmatic activity at depth came from geodetic surveys, which have detected a dome‐shaped uplift of 0.5 m centered near the resurgent dome: Langbein et al (1987), Savage et al (1987), Savage (1988), Wu and Wang (1988), Vasco et al (1988). Gravity and magnetotelluric surveys of Long Valley caldera were reported by Carle (1988), Hermance et al (1988), and Park and Torres‐Verdin (1988). Mortensen and Hopkins (1987) described an array of borehole tiltmeters that has been installed by the U.S.G.S.…”

Evidence for multiple boundary faults beneath the northwest moat of Long Valley Caldera: Magnetotelluric results

“…The boundaries of this elliptical basin are sharply delineated by steeply dipping normal faults which, for the most part, are buried and obscured by recent volcanic and sedimentary cover. The only evidence we have of these features is from their geophysical signatures on regional gravity, seismic and electromagnetic surveys (Pakiser, 1961;Hill, 1976;Kane et al, 1976;Hermance et al, 1984;Abers, 1985;Hill et al, 1985;Jachens and Roberts, 1985;Dawson et al, 1988;Hermance et al, 1988). Nevertheless, such studies have contributed substantially to characterizing the tectonic style of the caldera (Bailey, 1983;Rundle et al, 1986), its regional hydrology and geothermal potential (Sorey, 1985;Blackwell, 1985), and to structurally constraining patterns of seismicity and volcanism (see reviews by Hermance, 1983a;and Rundle and Hill, 1988).…”