SUMMARY Assessing seismic hazard in continental interiors is difficult because these regions are characterized by low strain rates and may be struck by infrequent destructive earthquakes. In this paper, we provide an example showing that interpretations of seismic cross sections combined with other kinds of studies such as analysis of microseismicity allow the whole seismogenic source area to be imaged in this type of region. The Middle Durance Fault (MDF) is an 80‐km‐long fault system located southeastern France that has a moderate but regular seismicity and some palaeoseismic evidence for larger events. It behaves as an oblique ramp with a left‐lateral‐reverse fault slip and has a low strain rate. MDF is one of the rare slow active fault system monitored by a dedicated dense velocimetric short period network. This study showed a fault system segmented in map and cross section views which consists of staircase basement faults topped by listric faults ramping off Triassic evaporitic beds. Seismic sections allowed the construction of a 3‐D structural model used for accurate location of microseismicity. Southern part of MDF is mainly active in the sedimentary cover. In its northern part and in Alpine foreland, seismicity deeper than 8 km was also recorded meaning active faults within the crust cannot be excluded. Seismogenic potential of MDF was roughly assessed. Resulting source sizes and estimated slip rates imply that the magnitude upper limit ranges from 6.0 to 6.5 with a return period of a few thousand years. The present study shows that the coupling between 3‐D fault geometry imaging and accurate location of microseismicity provides a robust approach to analyse active fault sources and consequently a more refined seismic hazard assessment.

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This paper describes observations of seismicity and casing failures associated with steam stimulation operations at Imperial Oil Ltd.'s Cold Lake oil field in Alberta, Canada. A total of 11 oil-producing pads were monitored over a 1 -2 year period using 3-component geophones cemented at depths ranging from 160 m to 400 m and data acquisition systems with a flat frequency response up to 1.5 kHz. Most of the seismicity was detected during the steaming operations and was located in the formation overlying the oil-bearing layer. Some activity was observed in the shales above, however, the reservoir itself showed almost no evidence of seismicity. The estimated seismic moment of the observed events was in the range 10 5 -10 7 N·m (−2.7BM B −1.3). According to a theoretical model and in situ observations, the seismic source corresponding to casing failure events should be well described by a dipole registering seismic moment in the order of 2 · 10 6 N·m. Seismic signals of a total of four observed casing failures were analyzed. The partial failures produced seismic moments slightly lower than this value while total failures were stronger by about one order of magnitude. The use of the SV/SH amplitude ratio, in conjunction with accurate source locations, provided a robust technique for the detection of casing failures.

Using records from the EURO-SEISTEST area near Thessaloniki (Greece), we studied empirically the amplification effects of a sedimentary valley. One of the main advantages of this site is the very detailed knowledge of the near-subsurface structure due to exhaustive geophysical and geotechnical measurements and data analyses (Jongmans et al., 1998). The uniqueness of the seismological data set is the very dense network: 31 stations were installed perpendicular and parallel to the valley axis, with minimum interstation distances of 250 m. The mean amplifications along both axes, estimated from 13 local events, were imaged using the traditional spectral ratio technique. Variations of the mean amplifications due to the choice of different data subsets were tested by the use of up to 89 local events, supplemented by four teleseismic events offering good low-frequency resolution. Results obtained using the traditional spectral ratio technique were compared with results from a generalized inversion technique, the H/V ratio technique, a coda wave technique, and Nakamura's technique. Advantages and disadvantages of each method are outlined, especially from a practical point of view.

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