We use cookies to ensure that we give you the best experience on our website. You can change your cookie settings at any time. Otherwise, we'll assume you're OK to continue.

Durham University

Department of Earth Sciences

Current Postgraduate Students

Publication details for Prof Gillian Foulger

Foulger, G.R, Julian, B.R, Hill, D.P, Pitt, A.M, Malin, P & Shalev, E (2004). Non-double-couple microearthquakes at Long Valley caldera, California, provide evidence for hydraulic fracturing. Journal of Volcanology and Geothermal Research 132(1): 45-71.

Author(s) from Durham


Most of 26 small (0.4M3.1) microearthquakes at Long Valley caldera in mid-1997, analyzed using data from a dense temporary network of 69 digital three-component seismometers, have significantly non-double-couple focal mechanisms, inconsistent with simple shear faulting. We determined their mechanisms by inverting P- and S-wave polarities and amplitude ratios using linear-programming methods, and tracing rays through a three-dimensional Earth model derived using tomography. More than 80% of the mechanisms have positive (volume increase) isotropic components and most have compensated linear-vector dipole components with outward-directed major dipoles. The simplest interpretation of these mechanisms is combined shear and extensional faulting with a volume-compensating process, such as rapid flow of water, steam, or CO2 into opening tensile cracks. Source orientations of earthquakes in the south moat suggest extensional faulting on ESE-striking subvertical planes, an orientation consistent with planes defined by earthquake hypocenters. The focal mechanisms show that clearly defined hypocentral planes in different locations result from different source processes. One such plane in the eastern south moat is consistent with extensional faulting, while one near Casa Diablo Hot Springs reflects en echelon right-lateral shear faulting. Source orientations at Mammoth Mountain vary systematically with location, indicating that the volcano influences the local stress field. Events in a �spasmodic burst� at Mammoth Mountain have practically identical mechanisms that indicate nearly pure compensated tensile failure and high fluid mobility. Five earthquakes had mechanisms involving small volume decreases, but these may not be significant. No mechanisms have volumetric moment fractions larger than that of a force dipole, but the reason for this fact is unknown.


Anderson, D.L., Archambeau, C.B., 1964. The anelasticity of
the Earth. J. Geophys. Res. 69, 2071^2084.
Arnott, S.K., Foulger, G.R., 1994. The Kra£a spreading segment,
Iceland: 2. The accretionary stress cycle and nonshear
earthquake focal mechanisms. J. Geophys. Res. 99,
Bailey, R.A., Dalrymple, G.B., Lanphere, M.A., 1976. Volcanism,
structure, and geochronology of Long Valley Caldera,
Mono County, California. J. Geophys. Res. 81, 725^744.
Barker, J.S., Langston, C.A., 1983. A teleseismic body wave
analysis of the May, 1980 Mammoth Lakes, California
earthquakes. Bull. Seismol. Soc. Am. 73, 419^434.
Barton, D.J., Foulger, G.R., Henderson, J.R., Julian, B.R.,
1999. Frequency-magnitude statistics and spatial correlation
dimensions of earthquakes at Long Valley caldera, California.
Geophys. J. Int. 138, 563^570.
Brace, W.F., Bombalakis, E.G., 1963. A note on brittle crack
growth in compression. J. Geophys. Res. 68, 3907^3913.
Claerbout, J.F., Muir, F., 1973. Robust modeling with erratic
data. Geophysics 38, 826^844.
Console, R., Rosini, R., 1998. Non-double-couple microearthquakes
in the geothermal ¢eld of Larderello, central Italy.
Tectonophysics 289, 203^220.
Denlinger, R.P., Riley, F.S., Boling, J.K., Carpenter, M.C.,
1985. Deformation of Long Valley caldera between August
1982 and August 1983. J. Geophys. Res. 90, 11199^
Dreger, D.S., Tkalcic, H., Johnston, M., 2000. Dilational processes
accompanying earthquakes in the Long Valley caldera.
Science 288, 122^125.
Ekstro«m, G., Dziewonski, A.M., 1983. Moment tensor solutions
of Mammoth Lakes earthquakes. EOS Trans. AGU
64, 262.
Farrar, C.D. et al., 1995. Forest-killing di¡use CO2 emission at
Mammoth Mountain as a sign of magmatic unrest. Nature
376, 675^678.
Foulger, G.R., 1988. Hengill triple junction, SW Iceland; 2.
Anomalous earthquake focal mechanisms and implications
for process within the geothermal reservoir and at accretionary
plate boundaries. J. Geophys. Res. 93, 13507^13523.
Foulger, G.R., Julian, B.R., 1993. Non-double-couple earthquakes
at the Hengill-Grensdalur volcanic complex, Iceland:
Are they artifacts of crustal heterogeneity? Bull. Seismol.
Soc. Am. 83, 38^52.
Foulger, G.R. et al., 2002. Three-dimensional crustal structure
of Long Valley caldera, California, and evidence for the
migration of CO2 under Mammoth Mountain. J. Geophys.
Res. 108, 2147, doi: 10.1029/2000JB0041.
Foulger, G.R., Long, R.E., 1984. Anomalous focal mechanisms;
tensile crack formation on an accreting plate boundary.
Nature 310, 43^45.
Foulger, G.R., Long, R.E., Einarsson, P., Bjo«rnsson, A., 1989.
Implosive earthquakes at the active accretionary plate
boundary in northern Iceland. Nature 337, 640^642.
Foulger, G.R., Malin, P.E., Shalev, E., Julian, B.R., Hill, D.P.,
1998. Seismic monitoring and activity increase in California
caldera. EOS Trans. AGU 79, 357^363.
Fuchs, K., Mu« ller, G., 1971. Computation of synthetic seismograms
with the re£ectivity method and comparison with
observations. Geophys. J. R. Astron. Sci. 23, 417^433.
Hill, D.P., 1996. Earthquakes and carbon dioxide beneath
Mammoth Mountain, California. Seismol. Res. Lett. 67,
Hill, D.P., Bailey, R.A., Ryall, A.S., 1985. Active tectonic
and magmatic processes beneath Long Valley caldera, eastern
California: An overview. J. Geophys. Res. 90, 11111^
Hill, D.P. et al., 1990. The 1989 earthquake swarm beneath
Mammoth Mountain, California: An initial look at the 4
May through 30 September activity. Bull. Seismol. Soc. Am.
80, 325^339.
Hudson, J.A., Pearce, R.G., Rogers, R.M., 1989. Source type
plot for inversion of the moment tensor. J. Geophys. Res.
94, 765^774.
Hung, S.-H., Forsyth, D.W., 1996. Non-double-couple focal
mechanisms in an oceanic, intraplate earthquake swarm:
Application of an improved method for comparative event,
moment tensor determination. J. Geophys. Res. 101, 25347^
Julian, B.R., 1983. Evidence for dyke intrusion earthquake
mechanisms near Long Valley caldera, California. Nature
303, 323^325.
Julian, B.R., 1986. Analysing seismic-source mechanisms by
linear-programming methods. Geophys. J. R. Astron. Sci.
84, 431^443.
Julian, B.R., 1994. Volcanic tremor: Nonlinear excitation by
£uid £ow. J. Geophys. Res. 99, 11859^11877.
Julian, B.R., Foulger, G.R., 1996. Earthquake mechanisms
from linear-programming inversion of seismic-wave amplitude
ratios. Bull. Seismol. Soc. Am. 86, 972^980.
Julian, B.R., Miller, A.D., Foulger, G.R., 1998. Non-doublecouple
earthquakes I: Theory. Rev. Geophys. 36, 525^549.
Julian, B.R., Sipkin, S.A., 1985. Earthquake processes in the
Long Valley caldera area, California. J. Geophys. Res. 90,
Knopo¡, L., Randall, M.J., 1970. The compensated linear
vector dipole: A possible mechanism for deep earthquakes.
J. Geophys. Res. 75, 4957^4963.
Kubas, A., Sipkin, S.A., 1987. Non-double-couple earthquake
mechanisms in the Nazca Plate subduction zone. Geophys.
Res. Lett. 14, 339^342.
Langbein, J., 1989. The deformation of the Long Valley caldera,
eastern California, from mid-1983 to mid-1988; measurements
using a two-color geodimeter. J. Geophys. Res.
94, 3833^3850.
Langbein, J., Hill, D.P., Parker, T.N., Wilkinson, S.K., 1993.
An episode of rein£ation of the Long Valley Caldera, Eastern
California: 1989^1991. J. Geophys. Res. 98, 15851^
Langbein, J.D., Dzurizin, D., Marshall, G., Stein, R., Rundle,
J., 1995. Shallow and peripheral volcanic sources of in£ation
revealed by modeling two-color geodimeter and leveling
data from Long Valley caldera, California, 1988^1992.
J. Geophys. Res. 100, 12487^12495.
Miller, A.D., 1996. Seismic Structure and Earthquake Focal
Mechanisms of the Hengill Volcanic Complex, SW Iceland.
Ph.D. Thesis, University of Durham, Durham, 280 pp.
Miller, A.D., Foulger, G.R., Julian, B.R., 1998a. Non-doublecouple
earthquakes. II: Observations. Rev. Geophys. 36,
Miller, A.D., Julian, B.R., Foulger, G.R., 1998b. Three-dimensional
seismic structure and moment tensors of non-doublecouple
earthquakes at the Hengill-Grensdalur volcanic complex,
Iceland. Geophys. J. Int. 133, 309^325.
Pitt, A.M., Hill, D.P., 1994. Long-period earthquakes in the
Long Valley caldera region, eastern California. Geophys.
Res. Lett. 21, 1679^1682.
Prejean, S.G., Ellsworth, W.L., 2001. Observations of earthquake
source parameters and attenuation at 2 km depth in
the Long Valley Caldera, eastern California. Bull. Seismol.
Soc. Am. 91, 165^177.
Ross, A., Foulger, G.R., Julian, B.R., 1996. Non-double-couple
earthquake mechanisms at The Geysers geothermal area,
California. Geophys. Res. Lett. 23, 877^880.
Ross, A., Foulger, G.R., Julian, B.R., 1999. Source processes
of industrially-induced earthquakes at The Geysers geothermal
area, California. Geophysics 64, 1877^1889.
Rundle, J.B., Hill, D.P., 1988. The geophysics of a restless
caldera ^ Long Valley, California. Annu. Rev. Earth Planet.
Sci. 16, 251^271.
Sammis, C.G., Julian, B.R., 1987. Fracture instabilities accompanying
dike intrusion. J. Geophys. Res. 92, 2597^2605.
Sanders, C.O., 1984. Location and con¢guration of magma
bodies beneath Long Valley, California, determined from
anomalous earthquake signals. J. Geophys. Res. 89, 8287^
Sanders, C.O., Ryall, F., 1983. Geometry of magma bodies
beneath Long Valley, California, determined from anomalous
earthquake signals. Geophys. Res. Lett. 10, 690^692.
Sarao' , A., Panza, G.F., Privitera, E., Cocina, O., 2001. Nondouble-
couple mechanisms in the seismicity preceding
the 1991^1993 Etna volcano eruption. Geophys. J. Int.
145, 319.
Savage, J.C., Cockerham, R.S., 1984. Earthquake swarm in
Long Valley caldera, California, January 1983: Evidence
for dike in£ation. J. Geophys. Res. 89, 8315^8324.
Shimizu, H., Matsuwo, N., Ohmi, S., Umakoshi, K. and Urabe,
T., 1988. A non double-couple seismic source: Tensileshear
crack formation in the Unzen volcanic region, Seismol.
Res. Lett., 5 pp.
Sibson, R.H., 1981. Fluid £ow accompanying faulting: Field
evidence and models. In: Earthquake Prediction ^ An International
Review. Maurice Ewing Series. AGU, Washington,
DC, pp. 593^603.
Sorey, M.L. et al., 1998. Carbon dioxide and helium emissions
from a reservoir of magmatic gas beneath Mammoth Mountain,
California. J. Geophys. Res. 103, 15303^15323.
Sorey, M.L., Farrar, C.D., Marshall, G.A., Howle, J.F., 1995.
E¡ects of geothermal development on deformation in the
Long Valley caldera, eastern California, 1985^1994. J. Geophys.
Res. 100, 12475^12486.
Sorey, M.L., Kennedy, B.M., Evans, W.C., Farrar, C.D.,
Suemnicht, G.A., 1993. Helium isotope and gas discharge
variations associated with crustal unrest in Long Valley caldera,
California, 1989^1992. J. Geophys. Res. 98, 15871^
Stroujkova, A.F., Malin, P.E., 2000. A magma mass beneath
Casa Diablo? Further evidence from re£ected seismic waves.
Bull. Seismol. Soc. Am. 90, 500^511.
Vavrycuk, V., 2002. Non-double-couple earthquakes of 1997
January in west Bohemia, Czech Republic: Evidence of tensile
faulting. Geophys. J. Int. 149, 364^373.
Waldhauser, F., Ellsworth, W.L., 2000. A double-di¡erence
earthquake location algorithm: Method and application to
the northern Hayward fault, California. Bull. Seismol. Soc.
Am. 90, 1353^1368.