Source characteristics of the 1992 Nicaragua tsunami earthquake inferred from teleseismic body waves |
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Authors: | Masayuki Kikuchi Hiroo Kanamori |
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Affiliation: | (1) Department of Physics, Yokohama City University, Seto, Kanazawa-ku, 236 Yokohama, Japan;(2) Seismological Laboratory, California Institute of Technology, 91125 Pasadena, California, USA |
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Abstract: | We analyzed the broadband body waves of the 1992 Nicaragua earthquake to determine the nature of rupture. The rupture propagation was represented by the distribution of point sources with moment-rate functions at 9 grid points with uniform spacing of 20 km along the fault strike. The moment-rate functions were then parameterized, and the parameters were determined with the least squares method with some constraints. The centroid times of the individual moment-rate functions indicate slow and smooth rupture propagation at a velocity of 1.5 km/s toward NW and 1.0 km/s toward SE. Including a small initial break which precedes the main rupture by about 10 s, we obtained a total source duration of 110 s. The total seismic moment isMo=3.4×1020 Nm, which is consistent with the value determined from long-period surface waves,Mo=3.7×1020 Nm. The average rise time of dislocation is determined to be 10 s. The major moment release occurred along a fault length of 160 km. With the assumption of a fault widthW=50 km, we obtained the dislocationD=1.3 m. From andD the dislocation velocity isD=D/0.1 m/s, significantly smaller than the typical value for ordinary earthquakes. The stress drop =1.1 MPa is also less than the typical value for subduction zone earthquakes by a factor of 2–3. On the other hand, the apparent stress defined by 2Es/Mo, where andEs are respectively the rigidity and the seismic wave energy, is 0.037 MPa, more than an order of magnitude smaller than . The Nicaragua tsunami earthquake is characterized by the following three properties: 1) slow rupture propagation; 2) smooth rupture; 3) slow dislocation motion. |
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Keywords: | Tsunami earthquake Nicaragua earthquake body wave inversion source process |
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