Four long seismic refraction profiles were shot in the Jordon‐Dead Sea‐Gulf of Elat graben and adjacent areas. From the arrival times of the Pg, Pn, and PmP phases, models of the crust and upper mantle were computed. The models show a crustal thickness of 30 km along the graben with a considerable thinning to the south along the Gulf of Elat. Between the Dead Sea, Red Sea, and the Mediterranean, the crust thickens, reaching a maximum thickness of 40 km west of the graben; but toward the Mediterranean, the crust thins rapidly to a thickness of 20 km while the overlying sediments thicken considerably. The results indicate an upper mantle upwelling in the graben area, connected to the Red Sea spreading mechanism, and the presence of a thin, possibly oceanic crust covered by a thick wedge of Mesozoic and Tertiary sediments underneath the Northern Negev of Israel and probably extending offshore to the Eastern Mediterranean.

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This paper presents those results from the 1974 Lithospheric Seismic Profde in Britain (LISPB) which relate to the compressional velocity structure of the crust and uppermost mantle beneath Northern Britain. A combination of interpretation techniques suitable for modelling laterally inhomogeneous media, including twodimensional ray-tracing and timeterm analysis, has resulted in a detailed seismic cross-section across the Caledonian orogenic belt. The main features of this section are a possible horizontal discontinuity in the Pre-Caledonian' basement, a change in the relationship between the lower crust and the uppermost mantle from north to south and a considerable thickening of the crust beneath the Caledonian fold belt. These results place considerable constraints upon tectonic models for the evolution of the Caledonides in particular in their implication of differing crustal structures north and south of the Southern Uplands and their indication of the primary significance of the Southern Uplands Fault. 44 mantle beneath Northern Britain. D. Barn ford et al .This paper presents LISPB results for the Pvelocity structure of the crust and uppermost 2 The LISPB experiment: data and travel-time correlationsThe LISPB experiment has been fully described in Bamford e l al. (1976) and Kaminski et al. (1976); that part of the experiment relevant to studies of the crust and uppermost mantle beneath Northern Britain in shown in Fig. I(a).In brief, during 1974 July and August, 60 German and British seismic stations (recording three components of ground motion on magnetic tape) occupied at different times the three segments ALPHA, BETA and GAMMA. Shots were fired at the various shotpoints to build up a series of reversed and overlapping crustal profiles (Fig. I@)) with observations out to at least 180 km distance, that is, sufficient for penetration to the Moho. In addition, a local earthquake (at KEQ - Fig. l(a)) was well recorded whilst the stations were occupying segments ALPHA and BETA and a single test profile had been completed in 1973 August using land shotpoint 2 and recording slightly to the east of GAMMA (Fig. l(a)).

We have constructed a composite image of the fault systems of the M 6.7 San Fernando (1971) and Northridge (1994), California, earthquakes, using industry reflection and oil test well data in the upper few kilometers of the crust, relocated aftershocks in the seismogenic crust, and LARSE II (Los Angeles Region Seismic Experiment, Phase II) reflection data in the middle and lower crust. In this image, the San Fernando fault system appears to consist of a decollement that extends 50 km northward at a dip of ϳ25؇ from near the surface at the Northridge Hills fault, in the northern San Fernando Valley, to the San Andreas fault in the middle to lower crust. It follows a prominent aseismic reflective zone below and northward of the main-shock hypocenter. Interpreted upward splays off this decollement include the Mission Hills and San Gabriel faults and the two main rupture planes of the San Fernando earthquake, which appear to divide the hanging wall into shingleor wedge-like blocks. In contrast, the fault system for the Northridge earthquake appears simple, at least east of the LARSE II transect, consisting of a fault that extends 20 km southward at a dip of ϳ33؇ from ϳ7 km depth beneath the Santa Susana Mountains, where it abuts the interpreted San Fernando decollement, to ϳ20 km depth beneath the Santa Monica Mountains. It follows a weak aseismic reflective zone below and southward of the mainshock hypocenter. The middle crustal reflective zone along the interpreted San Fernando decollement appears similar to a reflective zone imaged beneath the San Gabriel Mountains along the LARSE I transect, to the east, in that it appears to connect major reverse or thrust faults in the Los Angeles region to the San Andreas fault. However, it differs in having a moderate versus a gentle dip and in containing no mid-crustal bright reflections.