Open AccessBody wave inversion of the 1970 and 1963 South American large deep‐focus earthquakes
Author(s) -
Estabrook Charles H.
Publication year - 1999
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/1999jb900244
Subject(s) - seismology , geology , clockwise , deep focus earthquake , seismic moment , dipole , centroid , moment tensor , focal mechanism , geodesy , inversion (geology) , isotropy , subduction , fault (geology) , geometry , physics , tectonics , optics , amplitude , oceanography , mathematics , deformation (meteorology) , quantum mechanics
A comprehensive set of teleseismic waveforms from two South American deep‐focus earthquakes of the predigital era, the 1970 Colombia ( M w = 8.1) and 1963 Peru‐Bolivia ( M w = 7.7) events, are inverted for source mechanism, seismic moment, rupture history, and centroid depth. The P and SH wave inversion of the Colombia event confirms previous work, indicating that rupture occurred on a plane that dips steeply west. Rupture direction paralleled the trend of the Wadati‐Benioff zone. We decompose the source into subevents, based on a source time function which shows two major moment release pulses separated by ∼20 s. The first subevent is located near the initiation point at a depth of ∼630 km. The main moment release was located ∼70 km to the southeast and ∼20 km shallower. Rupture subsequently propagated farther southeast. The source time function has an initial subevent accounting for ∼30% of the moment release of the entire event, whereas the long‐period centroid moment tensor (CMT) analysis [ Russakoff et al. , 1997] has the initial subevent yielding ∼50%. The high‐angle nodal plane rotated ∼15° clockwise during the rupture, explaining the large compensated linear vector dipole (CLVD) component inferred from CMT solutions. Individual subevents have large CLVD and compressive isotropic components. A full moment tensor inversion of the Colombia and 1994 Bolivia events suggests that the initial subevents might contain a large non‐double‐couple (NDC) component. For the 1963 Peru‐Bolivia event, using P waves, rupture propagated NNW for a distance of ∼70 km, parallel to the high‐angle nodal plane and the trend of the Wadati‐Benioff zone. The focal mechanism changed dramatically after the second subevent, causing a very large NDC component. Both events, together with the 1994 Bolivia earthquake, have a precursor separated in space and time from the main rupture and show rupture velocities varying between 3 and 4 km/s between subevents, with <2.0 km/s on average for the entire event. Low seismic efficiencies and rupture velocities support a highly dissipative, temperature‐dependent rupture mechanism for large deep‐focus South American earthquakes, compared with events in cold subducting slabs.