TY - JOUR
T1 - Faulting processes during early-stage rifting
T2 - Seismic and geodetic analysis of the 2009-2010 Northern Malawi earthquake sequence
AU - Gaherty, J. B.
AU - Zheng, W.
AU - Shillington, D. J.
AU - Pritchard, M. E.
AU - Henderson, S. T.
AU - Chindandali, P. R.N.
AU - Mdala, H.
AU - Shuler, A.
AU - Lindsey, N.
AU - Oliva, S. J.
AU - Nooner, S.
AU - Scholz, C. A.
AU - Schaff, D.
AU - Ekström, G.
AU - Nettles, M.
N1 - Publisher Copyright:
© The Author(s) 2019. Published by Oxford University Press on behalf of The Royal Astronomical Society.
PY - 2019/2/27
Y1 - 2019/2/27
N2 - SUMMARY In December, 2009, a rare sequence of earthquakes initiated within the weakly extended Western Rift of the East African Rift system in the Karonga province of northern Malawi, providing a unique opportunity to characterize active deformation associated with intrabasinal faults in an early-stage rift. We combine teleseismic and regional seismic recordings of the largest events, InSAR imagery of the primary sequence, and recordings of aftershocks from a temporary (4-month) local network of six seismometers to delineate the extent and geometry of faulting. The locations of 1/41900 aftershocks recorded between January and May 2010 are largely consistent with a west-dipping normal fault directly beneath Karonga as constrained by InSAR and CMT fault solutions. However, a substantial number of epicentres cluster in an east-dipping geometry in the central part of the study area, and additional west-dipping clusters can be discerned near the shore of Lake Malawi, particularly in the southern part of the study area. Given the extensive network of hanging wall faults mapped in the Karonga region on the surface and in seismic reflection images, the distribution of events is strongly suggestive of multiple faults interacting to produce the observed deformation, and the InSAR data permit this but do not require it. We propose that fault interaction contributed to the seismic moment release as a series of M w 5-to-6 events instead of a normal main shock-aftershock sequence. We find the depth of fault slip during the main shocks constrained by InSAR peaks at less than 6 km, while the majority of recorded aftershocks are deeper than 6 km. This depth discrepancy appears to be robust and may be explained by fault interaction. Structural complexities associated with fault interaction may have limited the extent of coseismic slip during the main shocks, which increased stress deeper than the coseismic slip zone on the primary fault and synthetic faults to the east, causing the energetic aftershock series. There is no evidence of deformation at the Rungwe volcanic province 1/450 km north of the earthquake sequence between 2007 and 2010, consistent with previous interpretations of no significant magmatic contribution during the sequence.
AB - SUMMARY In December, 2009, a rare sequence of earthquakes initiated within the weakly extended Western Rift of the East African Rift system in the Karonga province of northern Malawi, providing a unique opportunity to characterize active deformation associated with intrabasinal faults in an early-stage rift. We combine teleseismic and regional seismic recordings of the largest events, InSAR imagery of the primary sequence, and recordings of aftershocks from a temporary (4-month) local network of six seismometers to delineate the extent and geometry of faulting. The locations of 1/41900 aftershocks recorded between January and May 2010 are largely consistent with a west-dipping normal fault directly beneath Karonga as constrained by InSAR and CMT fault solutions. However, a substantial number of epicentres cluster in an east-dipping geometry in the central part of the study area, and additional west-dipping clusters can be discerned near the shore of Lake Malawi, particularly in the southern part of the study area. Given the extensive network of hanging wall faults mapped in the Karonga region on the surface and in seismic reflection images, the distribution of events is strongly suggestive of multiple faults interacting to produce the observed deformation, and the InSAR data permit this but do not require it. We propose that fault interaction contributed to the seismic moment release as a series of M w 5-to-6 events instead of a normal main shock-aftershock sequence. We find the depth of fault slip during the main shocks constrained by InSAR peaks at less than 6 km, while the majority of recorded aftershocks are deeper than 6 km. This depth discrepancy appears to be robust and may be explained by fault interaction. Structural complexities associated with fault interaction may have limited the extent of coseismic slip during the main shocks, which increased stress deeper than the coseismic slip zone on the primary fault and synthetic faults to the east, causing the energetic aftershock series. There is no evidence of deformation at the Rungwe volcanic province 1/450 km north of the earthquake sequence between 2007 and 2010, consistent with previous interpretations of no significant magmatic contribution during the sequence.
KW - Africa
KW - Contintental tectonics: extensional
KW - Earthquake source observations
KW - Radar interferometry
KW - Seismicity and tectonics
UR - http://www.scopus.com/inward/record.url?scp=85064119151&partnerID=8YFLogxK
U2 - 10.1093/gji/ggz119
DO - 10.1093/gji/ggz119
M3 - 期刊論文
AN - SCOPUS:85064119151
SN - 0956-540X
VL - 217
SP - 1767
EP - 1782
JO - Geophysical Journal International
JF - Geophysical Journal International
IS - 3
ER -