Extreme runup from the 17 July 2006 Java tsunami

Geophysical Research Letters (Impact Factor: 4.46). 06/2007; 34(12):L12602. DOI: 10.1029/2007GL029404

ABSTRACT The 17 July 2006 magnitude Mw 7.8 earthquake off the south coast of western Java, Indonesia, generated a tsunami that effected over 300 km of coastline and killed more than 600 people, with locally focused runup heights exceeding 20 m. This slow earthquake was hardly felt on Java, and wind waves breaking masked any preceding withdrawal of the water from the shoreline, making this tsunami difficult to detect before impact. An International Tsunami Survey Team was deployed within one week and the investigation covered more than 600 km of coastline. Measured tsunami heights and run-up distributions were uniform at 5 to 7 m along 200 km of coast; however there was a pronounced peak on the south coast of Nusa Kambangan, where the tsunami impact carved a sharp trimline in a forest at elevations up to 21 m and 1 km inland. Local flow depth exceeded 8 m along the elevated coastal plain between the beach and the hill slope. We infer that the focused tsunami and runup heights on the island suggest a possible local submarine slump or mass movement.

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    ABSTRACT: The initial free-surface displacement generated by a submarine earthquake has a dipolar nature, which is computed analytically by Okada's solution [1] and is finite crested. The resulting leading long wave has an N-wave shape as noted by Tadepalli & Synolakis [2, 3]. Here, we present a simple analytical solution of the linear shallow-water wave equations over a constant depth to study the propagation of a finite strip source. We show the existence of focusing points of dipolar initial displacements, i.e. points where wave amplification may be observed, due to the directional focusing of three waves, namely a positive wave from the center of elevation part and two positive waves from the sides of depression. N-wave focusing is not restricted to linear non-dispersive wave theory, but can also be observed using nonlinear shallow-water wave theory and dispersive theory. The location of the focusing point depends on the strip length. The focusing mechanism is an inherent property of the initial waveform and thus is not caused by bathymetric lenses, which can have a significant combined effect on the evolution of earthquake-generated tsunamis. Using the 1998 Papua New Guinea, 2006 Java and 2011 Japan tsunamis as examples, we discuss the geophysical implications of the focusing and how this can be related to abnormal high run-up values observed during these events, which were insufficiently explained so far. [1] Okada, Y. 1985 Surface deformation due to shear and tensile faults in a half-space. Bull. Seism. Soc. Am. 75, 1135-1154. [2] Tadepalli, S. & Synolakis, C. E. 1994 The run-up of N-waves on sloping beaches. Proc. R. Soc. Lond. A 445, 99-112. [3] Tadepalli, S. & Synolakis, C. E. 1996 Model for the leading waves of tsunamis. Phys. Rev. Lett. 77, 2141-2144.
    EGU; 04/2013
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    ABSTRACT: In tsunami runup modelling there are still many open questions. Beside bathymetry the influence of the tsunami source description is an important issue. Widely used in tsunami modelling is Okada’s (1985) double-couple model. Usually, it is applied to the sea surface assuming that the sea bottom movement results in an abrupt deformation of the water surface, which is used as an initial condition for tsunami modelling. There may be more exact geophysical models, but as a first guess Okada’s method is advantageous because it is fast and has easy access to input parameters. That’s why it has been chosen to be first implemented in the tool, called QuakeGen. It calculates variable bathymetry with control of the temporary development of the earthquake. The time variable bathymetry was used to create a tsunami with the landslide module in MIKE 21. The results have been compared to the observed runup heights and arrival times from the 17 July 2006 Java Earthquake tsunami, chosen as a reference case. The generated waves are used as a boundary condition on one bathymetry just beside the generation zone. The runup heights are compared with field survey data reported in Fritz et al. (2007) and Lavigne et al. (2007). Furthermore, the influences of time step length during the simulation is investigated. Additionally to the MW = 7.7 earthquake, the first MW = 7.2 earthquake is included into the hydrodynamic simulation. A comparison of the results shows that the tsunami generated using QuakeGen and calculated with MIKE 21 gives the modeller the advantage of further adjustments by controlling the time in source modelling. The combination of QuakeGen and the MIKE 21 landslide module has been proven to yield more reliable results in simulation regarding runup and arrival time due to the possibility of considering all earthquakes which occured within the simulation period.
    International Conference on Tsunami Warning, Bali; 11/2008


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