Review of earthquake activity and current status of seismic monitoring in the region of the Bradley Lake Hydroelectric Project, southern Kenai Peninsula, Alaska, December 1981-May 1983
A project investigating seismic hazards in the Bradley Lake area of Kenai Peninsula is summarized. Hypocenters of 91 shallow (depth less than 20 km) earthquakes that occurred between December 1981 and May 1983 indicate that the pattern of recent crustal activity around the southern Kenai Peninsula has remained stable relative to the data prior to December 1981. The earthquakes are generally smaller than about magnitude 2.5. Most of the activity occurred east of the Border Ranges fault, and several concentrations can be observed in an otherwise diffuse distribution of activity. In general there is a poor correlation of the shallow activity with mapped fault traces. A more reliable estimate of the depth to the Benioff zone beneath Bradley Lake can be made from the greater number of available hypocenters of well-recorded earthquakes now available. Using the current velocity model, the depth to the top of the Benioff zone is 37 +- 5 km. A strong-motion record was obtained from the SMA-1 instrument co-located at the site of the central high-gain station BRLK, about 2 km from the proposed dam site. A preliminary estimate of 0.14 g (1 g = 980 cm/sec/sup 2/) was obtained for the maximum peak-to-peak horizontal acceleration on the record, but at present the event which caused the trigger is uncertain. Two new stations were installed southeast of Kachemak Bay in June 1983 in order to improve the accuracy of hypocenter determinations for continuing shallow earthquake activity that is observed in this area. 12 refs., 9 figs., 3 tabs.
- Research Organization:
- Geological Survey, Menlo Park, CA (USA)
- OSTI ID:
- 5750447
- Report Number(s):
- USGS-OFR-83-744; ON: TI85901340
- Country of Publication:
- United States
- Language:
- English
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