--> --> High-Resolution Seismic Imaging and Preliminary Geohazard Estimation Across the Three Bathymetric Archetypes Present Along the Israeli continental Slope

AAPG Geoscience Technology Workshop

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High-Resolution Seismic Imaging and Preliminary Geohazard Estimation Across the Three Bathymetric Archetypes Present Along the Israeli continental Slope

Abstract

Detailed geophysical imaging of the seafloor structural integrity and potential geo-hazards is a key element of offshore infrastructure development projects and site surveys. The desired imaging should be at a sub-meter resolution to allow its correlation with direct seafloor sampling (e.g., cores, CPT, etc.), but is also required to include the structural context to depths of tens to hundreds of meters below the seafloor. These combined requirements are not easily met by traditional or even modern (e.g., AUV based) imaging techniques. Here we demonstrate some superior results of exceptionally high (~0.3 m) resolution multichannel seismic surveys, obtaining ~300 m sub-seafloor imaging across the continental slope of Israel. We focus on three types of prominent features on the continental slope offshore Israel: 1) an open slope slide complex (the Goliath slide complex) offshore southern Israel; 2) the Dor Disturbance, a salt tectonics deformation focus, offshore northern central Israel; and 3) a submarine canyon offshore northern Israel. These features, located along prospective infrastructure development routes, are the three main archetypes of bathymetric features present along the continental slope offshore Israel. They portray a combination of substantial sub-seafloor thin skin faulting, acute bathymetric steps, and chaotic debris with substantial thicknesses. Surveying utilized 48 channels, 3.125 m group interval, Geo-Marine Survey Systems Geo-Sense streamer, and Geo Source 400 sparker, both utilizing the frequency content of 0.5 to 3 kHz. Pre-stack time migrated sections demonstrate the high-fidelity imaging and detailed insight given on these three complex features. In the Goliath slide complex area, on the southern Israeli continental slope, we map 13 generations of medium scale (estimated transported volume > 0.5 km3 and runout distance of >15 km) landslide events, estimated base on a well tie to have occurred within the last ~460 ka. Thus, giving a reoccurrence estimation of ~35 ka for medium scale submarine landslides in southern Israel. The most recent of these landslides features a sharp (~30⁰ angle) ~80 m high headscarp etched into the current seafloor, and correlates to thin-skin faults rooted in and above the Messenian salt. In the Dor disturbance region, the northern central Israeli continental slope, we map a small scale (estimated transported volume ~ 0.05 km3 and runout distance of ~5 km) retrogressive slide complex estimated to be younger than ~15 ka. The slide complex contains five sliding event generations, with an estimated reoccurrence of ~3 ka. Also observed in this region is a set of thin skin faults incising the continental slope accomodating tens of meters of offsets. Although most of these faults appear to be dormant, presumably since the early Holocene, several of them seem recently active, offseting the current seafloor by as much as 15 m. Moreover, the accomodated offset seems to change abruptly up the section, potentially implying significant catastrophic faults activity. In the canyons region of the northern Israeli continental slope we map >3 sequences of canyon headward erosion and small-scale collapses, giving evidence for episodic evolution of the canyon. Our results track the recent evolution of the main types of bathymetric features present along the continental slope offshore Israel, giving new preliminary geohazard estimates.