Seismic Source Directivity From Doppler Effect Analysis, Part II: Application To The Zemmouri-Boumerdes (Algeria) Earthquake of May 21st, 2003, Mw=6.8

Abstract

On May 21, 2003, the Eastern part of Algiers was struck by an earthquake (Mw=6.8) that injured 11.455 people and caused serious damage in cities close the hypocenter. The purpose of this work is to analyse the rupture directivity of this event using a Doppler Effect approach. The inversion method developed (DIRDOP) (Caldeira et al., 2004) allows an estimation of the rupture direction and velocity from a collection of time pulses, extracted from body waveforms or a relative source time function (RSTF). This seismic data has been downloaded from the IRIS consortium and has a reasonable azimuthal coverage. We have used 30 teleseismic broadband body wave data and 6 relative RSTF obtained from the deconvolution in the time domain (Borges, 2003) using the synthetic Green functions. These are calculated using the Haskell propagator matrix. The results show a bilateral rupture in the E-W direction. In the first 5 seconds the rupture propagates from the epicentre toward the East (N87oE +-13o) with an average velocity of 2.9 0.31km/s. In the last 10 seconds the rupture propagates with the same velocity but in the opposite direction (S84W+- 14o). Both results are coherent with the focal mechanism (strike=64o, dip=50o, rake=83o) and the seismic source obtained elsewhere (Bezzeghoud et al., 2004). REFERENCES Bezzeghoud M., B. Caldeira, J.F. Borges, A. Ayadi and E. Buforn. The Zemmouri-Boumerdes earthquake of may 21st, 2003, mw=6.8: source parameters and rupture propagation study from teleseismic data. XXIX General Assembly of the European Seis- mological Commission (ESC), 12-17 September, Potsdam, this issue. Borges J. F., 2003. Fonte sísmica em Portugal – algumas implicações na geodinâmica da região Açores-Gibraltar. PhD thesis, Universidade de Évora, p. 387 Caldeira B., M. Bezzeghoud and J. Borges, 2004. Seismic source directivity from Doppler effect analysis, part I: Theory. XXIX General Assembly of the European Seismological Commission (ESC), 12-17 September, Potsdam, this issue