HR: 0800h
AN: T31A-0272    [Abstracts]
TI: Double-Difference Relocation of an Earthquake Nest at Bucaramanga, Colombia: Interaction Between Two Slabs?
AU: * Zhang, J
EM: jian@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AU: Waldhauser, F
EM: felixw@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AU: Richards, P G
EM: richards@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AU: Schaff, D P
EM: dschaff@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AB: For an earthquake nest at Bucaramanga, Colombia, that has dimensions comparable to the uncertainty of global earthquake bulletins (> 10 km), teleseismic relocation with high precision is achieved by applying a double- difference (DD) algorithm to the pick arrival times from the EHB bulletin of Engdahl et al. (1998) and waveform cross-correlation (WCC) measurements of correlated earthquakes. DD relocations using phase picks alone have relative location uncertainty less than 4 km. They concentrate on a small fault-like volume that has approximate dimensions of 20km x 10km x 10km. A map view of the relocated seismicity shows an elongated structure striking at ~ 135 degree. An on-fault view indicates, on a vertical plane, an approximately 10 km thick band of seismicity, tilting ~ 40 degree to the SE and sub-parallel to the subducting Nazca plate in this area. Further location improvement for 33 correlated events obtained by including WCC measurements in the relocation procedure images a complex near-vertical seismic zone with a width of ~ 5 km. Global CMT solutions for 23 earthquakes within this small volume show highly variable focal mechanisms, independently indicating nonuniform slip within the zone. In general, however, the P axes align with the WSW-orientation of the relative movement between the Nazca and the Caribbean plate. We propose a slab-slab interaction model, in which the nest may represent a contact zone where the two subducting slabs collide and slide past each other.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting