Abstract
A microearthquake network with six stations and a diameter of about
50 km has been in operation in the Stiegler's Gorge area (Rufiji
Basin), Tanzania, between 1978 and 1981. The network, which used
radiotelemetry and digital recording at 30 Hz based on a triggering
system, has recorded a large number of teleseismic and regional earthquakes
in addition to several thousand local ones within the network. Most
of the locally recorded earthquakes are in the magnitude range 0-4
measured on a duration magnitude scale which has been developed for
the area, a scale which also satisfactorily covers regional earthquakes
with distance up to 25. An active and well-defined seismicity zone
has been delineated in the Stiegler's Gorge area, striking N140E
and dipping 45NE, with events distributed between 0 and 40 km in
depth. The time and space development of the local seismicity shows
a fairly stable pattern, and a detailed focal mechanism study within
the most active zone shows a predominance for normal faulting, with
east-west extensional movements. This is consistent with results
from local geological studies, even though there is no clear correlation
between the seismicity and locally mapped faults, and it is also
consistent with our knowledge of the regional tectonics of the East
African Rift System.
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