1887
Volume 36 Number 2
  • E-ISSN: 1365-2478

Abstract

ABSTRACT

The attenuation in the vicinity of the geothermal anomaly at Urach was determined by means of two near‐vertical reflection profiles. The attenuation in the sediments and in the upper crust (3‐4 km depth) was estimated by interpretation of the first (refracted) arrivals. For calculating the attenuation, the amplitude decay with respect to distance was used. Corrections for the spread factor, i.e. the geometric amplitude divergence was deduced from the traveltime curves. Below the anomaly, higher attenuation values (Q−1∼ 0.008) were observed compared with those in the undisturbed crust (Q−1∼ 0.002). This effect is probably due to the cracks and fissures in the upper part of the crystalline basement.

The attenuation in the middle and lower crust was determined using near‐vertical reflections from this depth interval. The use of the spectral ratio method leads to higher values of the effective attenuation Q−1 below the heat flow anomaly compared to those of the‘ normal’crust. This zone of high Q−1 coincides with the low velocity body below the heat flow anomaly. Both effects, the higher attenuation and the lower velocities, could be caused by high temperatures, cracks and fissures in the crust.

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2006-04-27
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