T Waves from the 1998 Papua New Guinea Earthquake and its Aftershocks: Timing the Tsunamigenic Slump

Abstract

T waves recorded at hydrophone and seismic stations following the Papua New Guinea earthquake of 17 July 1998 and its aftershocks show that a small event at 09:02 GMT featured source properties incompatible with an elastic dislocation of appropriate body-wave magnitude (m b ¼ 4:4). These include an exceptional duration (47 s at the Wake Island hydrophone station WK31), a spectrum rich in high frequencies (7 to 12 Hz), and a generally low spectral amplitude. These characteristics can be explained by the model of an underwater slump, accelerating from a standstill and eventually slowing down. The relocation of the 09:02 event is compatible with its location within an amphitheater inside which shipboard cruises in 1998 and 1999 documented the presence of a 4 -km 3 geologically fresh slump. We propose that the slump took place at 09:02 on 17 July 1998, i.e., 13 minutes after the mainshock, and that it generated the locally catastrophic tsunami, whose properties (amplitude and distribution of runup; timing) could not be explained by a dislocation model.

Landslide tsunami hazard in the Indonesian Sunda Arc

“…Further, hydroacoustic wave records at Wake Island have been identified to represent the seismic signal of the submarine slump (Okal, 1999). The thereby associated timing of the mass failure corresponds very well to eyewitness accounts of tsunami arrival, as numerical tsunami modeling shows (Synolakis et al, 2002;Okal, 2003). Recent geometry interpretations revealed slump width, length and thickness of 4.2, 4.5, and 0.75 km, respectively, resulting in a slide volume of 6.4 km 3 (Tappin et al, 2008).…”

“…As the released seismic energy is usually very small, seismic stations are not effective in detecting slope failures. Okal (2003) identified landslide signals in hydrophone and seismic data, but the technique is not yet applicable in real time. Based on numerical modeling, Brune et al (2009c) showed that tiltmeters can be used to detect a landslide in the course of the event.…”

A Potential Tsunami impact assessment of submarine landslide at Baiyun Depression in Northern South China Sea

“…about submarine landslides and tsunami have been continuously deepened (Prior 1984;Ward 2001;Okal 2003;Ward and Day 2003;Masson et al 2006;Uriten et al 2009;Vanneste et al 2011;Sue et al 2011). In this paper, achievements of Grilli and Watts (2005), Enet et al (2003) and Enet & Grilli (2007) relating to submarine landslidegenerated tsunamis are used as reference.…”

The 1998 Papua New Guinea Earthquake and its Fault Plane Estimated from Relocated Aftershocks

“…Since the dipping direction of the fault plane is S56°W, as shown by the arrow, and the shallowest part of the main shock fault is close to the 40 km fault, there is a possibility that the fault relates to the event. OKAL (1999OKAL ( , 2001 proposed that the seismic event at 09:02 GMT is a slump event that occurred in an amphitheater identified by OKAL (2001) and then caused the severe tsunami. Although the standard error for the focal depth is large, the 09:02 event was located at a shallower depth than the other three events shown in Figure 6.…”