Local tsunamis and distributed slip at the source
Geist, E.L.; Dmowska, R. (1999). Local tsunamis and distributed slip at the source, in: Sauber, J. et al. Seismogenic and tsunamigenic processes in shallow subduction zones. Pure and Applied Geophysics, 154(3-4): pp. 485-512. https://dx.doi.org/10.1007/978-3-0348-8679-6_6 In: Sauber, J.; Dmowska, R. (Ed.) (1999). Seismogenic and tsunamigenic processes in shallow subduction zones. e-Book edition. Pure and Applied Geophysics, 154(3-4). Springer: Basel. ISBN 978-3-0348-8679-6. vi, 405-776 pp. https://dx.doi.org/10.1007/978-3-0348-8679-6, more In: Pure and Applied Geophysics. Birkhäuser: Basel. ISSN 0033-4553; e-ISSN 1420-9136, more |  |
| Keyword | | | Author keywords | Tsunami coseismic displacement source parameters nonuniform slip crack tsunami runup |
| Abstract | Variations in the local tsunami wave field are examined in relation to heterogeneous slip distributions that are characteristic of many shallow subduction zone earthquakes. Assumptions inherent in calculating the coseismic vertical displacement field that defines the initial condition for tsunami propagation are examined. By comparing the seafloor displacement from uniform slip to that from an ideal static crack, we demonstrate that dip-directed slip variations significantly affect the initial cross-sectional wave profile. Because of the hydrodynamic stability of tsunami wave forms, these effects directly impact estimates of maximum runup from the local tsunami. In most cases, an assumption of uniform slip in the dip direction significantly underestimates the maximum amplitude and leading wave steepness of the local tsunami. Whereas dip-directed slip variations affect the initial wave profile, strike-directed slip variations result in wavefront-parallel changes in amplitude that are largely preserved during propagation from the source region toward shore, owing to the effects of refraction. Tests of discretizing slip distributions indicate that small fault surface elements of dimensions similar to the source depth can acceptably approximate the vertical displacement field in comparison to continuous slip distributions. Crack models for tsunamis generated by shallow subduction zone earthquakes indicate that a rupture intersecting the free surface results in approximately twice the average slip. Therefore, the observation of higher slip associated with tsunami earthquakes relative to typical subduction zone earthquakes of the same magnitude suggests that tsunami earthquakes involve rupture of the seafloor, whereas rupture of deeper subduction zone earthquakes may be imbedded and not reach the seafloor. |
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