Imaging the complexity of an active normal fault system: The 1997 Colfiorito (central Italy) case study

被引:148
作者
Chiaraluce, L
Ellsworth, WL
Chiarabba, C
Cocco, M
机构
[1] Ist Nazl Geofis & Vulcanol, I-00143 Rome, Italy
[2] US Geol Survey, Menlo Pk, CA 94025 USA
[3] Univ Perugia, Dipartimento Sci Terra, I-06100 Perugia, Italy
关键词
normal faults; segmentation; seismicity; double-difference location; stress inversion;
D O I
10.1029/2002JB002166
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
[1] Six moderate magnitude earthquakes (5 < M-w < 6) ruptured normal fault segments of the southern sector of the North Apennine belt (central Italy) in the 1997 Colfiorito earthquake sequence. We study the progressive activation of adjacent and nearby parallel faults of this complex normal fault system using similar to1650 earthquake locations obtained by applying a double-difference location method, using travel time picks and waveform cross-correlation measurements. The lateral extent of the fault segments range from 5 to 10 km and make up a broad, similar to45 km long, NW trending fault system. The geometry of each segment is quite simple and consists of planar faults gently dipping toward SW with an average dip of 40degrees -45degrees. The fault planes are not listric but maintain a constant dip through the entire seismogenic volume, down to 8 km depth. We observe the activation of faults on the hanging wall and the absence of seismicity in the footwall of the structure. The observed fault segmentation appears to be due to the lateral heterogeneity of the upper crust: preexisting thrusts inherited from Neogene's compressional tectonic intersect the active normal faults and control their maximum length. The stress tensor obtained by inverting the six main shock focal mechanisms of the sequence is in agreement with the tectonic stress active in the inner chain of the Apennine, revealing a clear NE trending extension direction. Aftershock focal mechanisms show a consistent extensional kinematics, 70% of which are mechanically consistent with the main shock stress field.
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页数:19
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