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Submarine Landslides in the Santa Barbara Channel As Potential Tsunami Sources H Submarine landslides in the Santa Barbara Channel as potential tsunami sources H. G. Greene, L. Y. Murai, P. Watts, N. A. Maher, M. A. Fisher, C. E. Paull, P. Eichhubl To cite this version: H. G. Greene, L. Y. Murai, P. Watts, N. A. Maher, M. A. Fisher, et al.. Submarine landslides in the Santa Barbara Channel as potential tsunami sources. Natural Hazards and Earth System Sciences, Copernicus Publ. / European Geosciences Union, 2006, 6 (1), pp.63-88. hal-00299251 HAL Id: hal-00299251 https://hal.archives-ouvertes.fr/hal-00299251 Submitted on 16 Jan 2006 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Natural Hazards and Earth System Sciences, 6, 63–88, 2006 SRef-ID: 1684-9981/nhess/2006-6-63 Natural Hazards European Geosciences Union and Earth © 2006 Author(s). This work is licensed System Sciences under a Creative Commons License. Submarine landslides in the Santa Barbara Channel as potential tsunami sources H. G. Greene1, L. Y. Murai2, P. Watts3, N. A. Maher4, M. A. Fisher5, C. E. Paull1, and P. Eichhubl6 1Monterey Bay Aquarium Research Institute (MBARI), 7700 Sandholdt Road, Moss Landing, CA 95039; Moss Landing Marine Laboratories, 8272 Moss Landing Road Moss Landing, CA 95039, USA 2Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039, USA 3Applied Fluids Engineering, Inc., 5710 E. 7th Street, PMB #237, Long Beach, CA 90803, USA 4AOA Geophysics, Inc., 7532 Sandholdt Road, Moss Landing, CA 95039, USA 5United States Geological Survey, MS 999, 345 Middlefield Road, Menlo Park, CA 94025, USA 6Stanford University, Department of Geological and Environmental Sciences, Stanford, CA 94305, USA Received: 13 June 2005 – Revised: 26 October 2005 – Accepted: 15 November 2005 – Published: 16 January 2006 Part of Special Issue “Tsunami hazard from slope instability” Abstract. Recent investigations using the Monterey Bay Several other smaller (2 km2 and 4 km2) slides are located Aquarium Research Institutes (MBARI) Remotely Operated on the northern flank of the Santa Barbara Basin, both to the Vehicles (ROVs) “Ventana” and “Tiburon” and interpreta- west and east of Goleta slide and on the Conception fan along tion of MBARI’s EM 300 30 kHz multibeam bathymetric the western flank of the basin. One slide, named the Gaviota data show that the northern flank of the Santa Barbara Basin slide, is 3.8 km2, 2.6 km long and 1.7 km wide. A distinct has experienced massive slope failures. Of particular con- narrow scar extends from near the eastern head wall of this cern is the large (130 km2) Goleta landslide complex lo- slide for over 2 km eastward toward the Goleta slide and may cated off Coal Oil Point near the town of Goleta, that mea- represent either an incipient failure or a remnant of a previ- sures 14.6-km long extending from a depth of 90 m to nearly ous failure. Push cores collected within the main head scar 574 m deep and is 10.5 km wide. We estimate that approxi- of this slide consisted of hydrogen sulfide bearing mud, pos- mately 1.75 km3 has been displaced by this slide during the sibly suggesting active fluid seepage and a vibra-core pen- Holocene. This feature is a complex compound submarine etrated ∼50 cm of recent sediment overlying colluvium or landslide that contains both surfical slump blocks and mud landslide debris confirming the age of ∼300 years as pro- flows in three distinct segments. Each segment is composed posed by Lee et al. (2004). However, no seeps or indications of a distinct head scarp, down-dropped head block and a slide of recent movement were observed during our ROV investi- debris lobe. The debris lobes exhibit hummocky topogra- gation within this narrow head scar indicating that seafloor in phy in the central areas that appear to result from compres- the scar is draped with mud. sion during down slope movement. The toes of the western and eastern lobes are well defined in the multibeam image, whereas the toe of the central lobe is less distinct. Continu- 1 Introduction ous seismic reflection profiles show that many buried slide debris lobes exist and comparison of the deformed reflec- The concept of submarine landslides as major sources of tors with ODP Drill Site 149, Hole 893 suggest that at least tsunamis has recently reached a new high. This present con- 200 000 years of failure have occurred in the area (Fisher et cern is based on the disastrous July 1998 tsunami in Papua al., 2005a). Based on our interpretation of the multibeam New Guinea that completely destroyed the villages around bathymetry and seismic reflection profiles we modeled the Sissano Lagoon and killed over 2200 people. Based on ex- potential tsunami that may have been produced from one of tensive offshore investigations after the event, the tsunami the three surfical lobes of the Goleta slide. This model shows probably was produced by a large submarine landslide lo- that a 10 m high wave could have run ashore along the cliffs cated offshore from the village and triggered in part by a of the Goleta shoreline. widely felt M7 earthquake (Tappen et al., 1999, 2001; Syno- lakis et al., 2002; Davies et al., 2003). Within about 10 min of Correspondence to: H. G. Greene the offshore failure and around 30 min after the main shock, ([email protected]) a wave some 10 m high inundated the low-lying spit and 64 H. G. Greene et al.: Potential tsunamigenic landslides 121o 0'0"W 121o 30'0"W 121o 0'0"W run-up elevation, a seafloor failure needs to be in interme- diate to shallow water depths, be generally no deeper than 1000 m, be of significant volume (i.e., greater than 2 km3), consist of stiff cohesive materials such as firm clay, and ac- Pt. Arguello celerate rapidly (Watts et al., 2000, Ward, 2001; Greene and o 34 30'0"N o Pt. Conception Santa Ward, 2003). Rules of thumb for landslide tsunami ampli- 34 30'0"N Barbara tudes are hard to come by because there are many different length scales that impact tsunami amplitude (Watts, 2004c). Although much work, as noted above, has been done on FIG. 12 FIG. FIG. 15 FIG. FIG. 5, 14a, 16 FIG. 4 specific submarine landslides to determine their history and cause of failure, much more work is needed to determine Channel Islands platform how a failure disintegrates and what the potential is for future San Miguel Island o mass movements. New technology, such as high-resolution 34 0'0"N o Santa Cruz Island 34 0'0"N Kilometers digital multibeam bathymetric and backscatter mapping sys- 10 5 0 10 20 30 OIL PLATFORM Santa Rosa Island tems, have produced images of many of the previously stud- 121o 0'0"W 121o 30'0"W 121o 0'0"W ied landslides and have detected many others. These images exhibit such high-resolution (on the order of meters) features Fig. 1. Computer generated artificial sun-shaded relief image of that the texture and detailed morphology of a slide surface the Santa Barbara Channel from Simrad EM300 30 kHz multibeam can be resolved. In addition, modern observational and sam- bathymetric data showing area of study, oil platforms, and principal pling capabilities provided with remotely operated vehicles geographic locations. Cross-like symbols represent oil platforms. Boxes show location of other figures. (ROVs) allow for specific and selective sampling. We used such technologies to study the northern flank of the Santa Barbara Basin, an area of extensive mass wasting (Fig. 1). While tsunamigenic landslides are generally thought to lagoon along which the villages were located and stimulated be triggered through seismic loading, many tsunamis can a world wide call for the study of such phenomenon so that be generated from non-seismic related submarine failures. future calamities can be prevented, or at least predicted and Other mechanisms that can stimulate mass movement on the mitigated. This call has again been renewed after the “Box- seafloor include loading of slope sediment by storm waves or ing Day” 26 December 2004 Sumatra M9+ earthquake that hurricanes, elevated sediment pore pressures from dewater- produced the Indian Ocean tsunami that left nearly 275 000 ing in response to tectonic compression or rapid increase of people dead or missing and more than a million others home- overburden pressures, reduction of stress by bubble phase gas less. expansive pressures, artesian pressures, seepage forces, gas It has long been known that submarine failures within re- hydrate disassociation, and sediment accumulations exceed- stricted bodies of waters such as bays and fiords regularly ing the angle-of-repose. If these non-seismogenic failures occur forming distinct seafloor scars (Shepard, 1933; Hamp- are large enough and accelerate rapidly enough, a tsunami ton et al., 1993; Prior et al., 1978, 1982; Plafker et al., can be produced. However, along active plate margins, such 1969). Delta fronts exhibit slide scars produced from low as in the Santa Barbara Basin region, seismicity can play a angle failures of weak, fine-grained sediment (Prior et al., major role in generating tsunamigenic landslides. 1981). Failures on volcanic island flanks (Moore et al., 1989, The objectives of this study are to describe mass wasting 1994; Silver et al., 2005) and along the upper continental along the northern flank of the Santa Barbara Basin using slope (Field and Edwards, 1980; Schwab et al., 1993; Lee recently acquired multibeam data, seismic reflection profiles, et al., 1993, 2003; Field et al., 1999; Hampton and Bouma, ROV observations and seafloor samples collected by ROVs, 1977; Hampton et al., 1996) are also well known.
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