The Mw 6.7 George Sound earthquake of October 15, 2007
Response and preliminary results
The Mw 6.7 George Sound earthquake of October 15, 2007, occurred only a few kilometres offshore of Fiordland, within a region where the subduction zone of the Australian Plate beneath the Pacific Plate intersects the offshore extension of the Alpine Fault. Rapid response deployments of portable seismographs, a strong motion recorder and GPS receivers relatively close to the epicentre soon after the main shock allowed us to relate the event to thrusting at the subduction interface. The main shock moment tensor solution places the event at a shallow depth of 21 km. The sequence of aftershocks that followed the main event presents predominantly reverse faulting mechanisms with depths of 20 to 25 km. Earthquake re-locations using data recorded by the portable seismometers reveal a cluster of aftershocks at 17 to 25 km. This cluster defines a steeply SE-dipping plane, while another cluster at about 7-12 km depth images a NW-dipping plane within the overlying plate. Preliminary results from the seismic, geodetic and near-field strong motion geophysical data are consistent with rupture on an east dipping fault plane, presumed to be the subduction interface.
Reyners, M., Gledhill, K. & Waters, D. (1991). “Tearing of the Subducted Australian Plate during the Te Anau, New Zealand, Earthquake of 1988 June 3”. Geophysical Journal International 104 (1): 105-115. DOI: https://doi.org/10.1111/j.1365-246X.1991.tb02497.x
Robinson, R., Webb, T., McGinty, P., Cousins, J. & Eberhart-Phillips, D. (2003) “The 2000 Thompson Sound Earthquake, New Zealand”. New Zealand Journal of Geology & Geophysics 46: 331–341. DOI: https://doi.org/10.1080/00288306.2003.9515013
Reyners, M. & Webb, T. (2002) “Large earthquake near Doubtful Sound, New Zealand 1989-93”. New Zealand Journal of Geology and Geophysics 45: 109-120. DOI: https://doi.org/10.1080/00288306.2002.9514963
McGinty, P. & Robinson, R. (2007) “The 2003 Mw 7.2 Fiordland subduction earthquake, New Zealand: aftershock distribution, main shock fault plane and static stress changes on the overlying Alpine Fault”. Geophysical Journal International 169: 579–592. DOI: https://doi.org/10.1111/j.1365-246X.2007.03336.x
Reyners, M., McGinty, P., Cox, S., Turnbull, I., O’Neill, T., Gledhill, K., Hancox, G., Beavan, J., Matheson, D., McVerry, G., Cousins, J., Zhao, J., Cowan, H., Caldwell, G., Bennie, S. & the GeoNet team (2003) “The MW7.2 Fiordland earthquake of August 21, 2003: Background and preliminary results”. Bulletin of the New Zealand Society of Earthquake Engineering 36(4): 233-248. DOI: https://doi.org/10.5459/bnzsee.36.4.233-248
Beavan, J., Tregoning, P., Bevis, M., Kato, T. & Meertens, C. (2002) “Motion and rigidity of the Pacific plate and implications for plate boundary deformation”. Journal of Geophysical Research 107 (B10), 2261, doi:10.1029/2001JB000282. DOI: https://doi.org/10.1029/2001JB000282
DeMets, C., Gordon, R., Argus, D. & Stein, S. (1994) "Effect of recent revisions to the geomagnetic reversal time scale on estimates of current plate motions". Geophysical Research Letters 21: 2191-2194. DOI: https://doi.org/10.1029/94GL02118
Eberhart-Phillips & Reyners (2001) “A complex, young subduction zone imaged by three-dimensional seismic velocity, Fiordland, New Zealand”. Geophysical Journal International 146: 731–746. DOI: https://doi.org/10.1046/j.0956-540x.2001.01485.x
Reyners, M., Robinson, R., Pancha, A. & McGinty, M. (2002) "Stresses and strains in a twisted subduction zone - Fiordland, New Zealand". Geophysical Journal International 148: 637-648. DOI: https://doi.org/10.1046/j.1365-246X.2002.01611.x
Massonnet, D. & Feigl, K. (1998) “Radar interferometry and its application to changes in the Earth surface”. Reviews of Geophysics 36(4): 441-500. DOI: https://doi.org/10.1029/97RG03139
Rosen, P.A., Hensley, S., Joughin, I.R., Li, F.K., Madsen, S.N., Rodriguez, E. & Goldstein, R.M. (2000) “Synthetic aperture radar interferometry”. Proceedings of the IEEE 88 (3): 333-382. DOI: https://doi.org/10.1109/5.838084
Ristau, J. (2008) “Implementation of routine regional moment tensor analysis in New Zealand”. Seismological Research Letters 79: 400-415. DOI: https://doi.org/10.1785/gssrl.79.3.400
Dreger, D. & Helmberger, D.V. (1993) “Determination of source parameters at regional distances with single station or sparse network data”. Journal of Geophysical Research 98: 8107-8125. DOI: https://doi.org/10.1029/93JB00023
Pasyanos, M.E., Dreger, D.S. & Romanowicz, B. (1996) “Towards real-time determination of regional moment tensors”. Bulletin of the Seismological Society of America 86: 1255-1269.
Dreger, D.S. (2003) “TDMT_INV: Time Domain Seismic Moment Tensor INVersion”. Internation Handbook of Earthquake and Engineering Seismology 81 B: 1627. DOI: https://doi.org/10.1016/S0074-6142(03)80290-5
Samsonov, S., Tiampo, K., Rundle, J. & Li, Z. (2007) “Application of DInSAR-GPS optimization for derivation of fine scale surface motion maps of southern California”. Transactions on Geoscience and Remote Sensing 45 (2): 512-521. DOI: https://doi.org/10.1109/TGRS.2006.887166
Goldstein, R.M. & Werner, C.L. (1998) “Radar Interferogram Filtering for Geophysical Applications”. Geophysical Research Letters 25 (21): 4035-4038. DOI: https://doi.org/10.1029/1998GL900033
Beavan, J. & Haines, J. (2001) “Contemporary horizontal velocity and strain-rate fields of the Pacific-Australian plate boundary zone through New Zealand”. Journal of Geophysical Research 106 (B1): 741–770. DOI: https://doi.org/10.1029/2000JB900302
Darby, D. J. & Beavan, J. (2001) “Evidence from GPS measurements for contemporary plate coupling on the southern Hikurangi subduction thrust and partitioning of strain in the upper plate”. Journal of Geophysical Research 106 (B12): 30,881-30,891. DOI: https://doi.org/10.1029/2000JB000023
McCaffrey, R. (1995) “DEFNODE users guide”. Rensselaer Polytechnic Institute, Troy, New York, www.rpi.edu/~mccafr/defnode.
McCaffrey, R. (2002) “Crustal block rotations and plate coupling, in Plate Boundary Zones”. Eds. S. Stein and J. Freymueller, AGU Geodynamics Series 30: 100-122.
Gledhill, K. (1985) "An earthquake detector employing frequency domain techniques". Bulletin of the Seismological Society of America 75 (6): 1827-1835.
Barnes, P.M., Sutherland, R., Delteil, J. (2005) “Strike-slip structure and sedimentary basins of the southern Alpine Fault, Fiordland, New Zealand”. Geological Society of America 117 (3/4): 411-435. DOI: https://doi.org/10.1130/B25458.1
Francois-Holden, C., Di Carli, S., Sladen A. & Madariaga R. (2008) “Non linear kinematic source inversion of the 2000 Tottori, Japan earthquake”. - submitted Geophysical Research Letters.
Peyrat, S. & Favreau, P. “Kinematic and spontaneous rupture models of the 2005 Tarapaca intermediate depth earthquake” -submitted Geophysical Journal International.
Wessel, P. & Smith, W.H.F. (1998) “New, improved version of the Generic Mapping Tools”. EOS Transactions of the American Geophysical 79: 579.2 DOI: https://doi.org/10.1029/98EO00426