TY - JOUR
T1 - The 1994-1995 manyaraand KwaMtoro earthquake swarms
T2 - Variation in the depth extent of seismicity in northern Tanzania
AU - Mulibo, G. D.
AU - Nyblade, A. A.
PY - 2009/12
Y1 - 2009/12
N2 - Seismicity within two earthquake swarms (mb 1.0 to 4.0) in northern Tanzania recorded by the 1994-1995 Tanzania Broadband Seismic Experiment has been investigated through event relocation, modelling of regional depth phases and examination of focal mechanisms. In the Manyara swarm, seismicity is distributed over a region ∼20 km wide and extends to >30 km depth. Hypocenters correlate well with the Manyara Rift, and focal mechanisms of many events show normal faulting with nodal planes having the same north-northeast orientation as the Manyara Rift border fault. This result indicates that the events are consistent with slip along the border fault and related faults beneath the Manyara Rift, and shows that the faults extend into the lower crust. Seismicity in the KwaMtoro swarm is distributed over a region ∼10 km wide but extends only to ∼12 km depth. There are no mapped faults above the swarm, but a strong correlation between the north to south orientation of the swarm, the north to south orientation of nodal planes in focal mechanisms, and north to south striking extensional structures nearby, suggest that events in this swarm could be caused by slip on a system of rift faults. However, a magma-driven origin for either swarm cannot be ruled out either.
AB - Seismicity within two earthquake swarms (mb 1.0 to 4.0) in northern Tanzania recorded by the 1994-1995 Tanzania Broadband Seismic Experiment has been investigated through event relocation, modelling of regional depth phases and examination of focal mechanisms. In the Manyara swarm, seismicity is distributed over a region ∼20 km wide and extends to >30 km depth. Hypocenters correlate well with the Manyara Rift, and focal mechanisms of many events show normal faulting with nodal planes having the same north-northeast orientation as the Manyara Rift border fault. This result indicates that the events are consistent with slip along the border fault and related faults beneath the Manyara Rift, and shows that the faults extend into the lower crust. Seismicity in the KwaMtoro swarm is distributed over a region ∼10 km wide but extends only to ∼12 km depth. There are no mapped faults above the swarm, but a strong correlation between the north to south orientation of the swarm, the north to south orientation of nodal planes in focal mechanisms, and north to south striking extensional structures nearby, suggest that events in this swarm could be caused by slip on a system of rift faults. However, a magma-driven origin for either swarm cannot be ruled out either.
UR - http://www.scopus.com/inward/record.url?scp=77952966263&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=77952966263&partnerID=8YFLogxK
U2 - 10.2113/gssajg.112.3-4.387
DO - 10.2113/gssajg.112.3-4.387
M3 - Article
AN - SCOPUS:77952966263
SN - 1012-0750
VL - 112
SP - 387
EP - 404
JO - South African Journal of Geology
JF - South African Journal of Geology
IS - 3-4
ER -