کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
6433414 | 1636721 | 2016 | 13 صفحه PDF | دانلود رایگان |
- A sequence of unusual, moderate-size earthquakes occurred in a seismically quiet area offshore western Corsica.
- The sequence includes the largest earthquake ever instrumentally recorded in the area.
- A reverse faulting mechanism is consistent with shortening between the Corsica-Sardinia block and the European continent.
- Determination of a 6-13Â km focal depth from 3 different methods for the mainshock (2011/07/07, ML 5.3).
- No fault is known in the epicentral area from MCS profiles.
A new seismically active zone is found in the southern part of the Ligurian basin, 80-km west of Corsica (western Mediterranean). The activity began in February 2011 with a foreshock (ML 4) and a mainshock (ML 5.3) 5Â days later, followed by numerous aftershocks. We first analyze the fore- and mainshock in detail. We compare the results obtained using classical methods (linear location in a 1D medium and focal mechanisms from P and S polarities) and new approaches (non-linear location in a 3D medium and waveform modeling for determining the seismic moment and the focal mechanism). Both methods provided similar results for location, depth (in the range of 6-13Â km) and focal mechanisms, which reveal reverse faulting with nodal planes oriented N-S and NE-SW. We then locate 27 of the aftershocks in the 3D model and find a 10-km-long NE-SW alignment with a depth between 7 and 16Â km. In 2012 and 2013, three other moderate-size events (ML 3.8, 4 and 4.5) occurred and confirm that this zone is still active. The epicentral area is located in the oceanic domain of the Ligurian Basin. From analysis of the bathymetry and high-resolution multi-channel seismic profiles, no morphologic anomaly at surface and no inherited fault in the shallow ~Â 4Â km depth were imaged, which suggest that no significant deformation occurred in the area since 5Â Ma. Thus, the structure(s) activated during the 2011-2013 sequence remain unknown. In light of these results, we point out a notable difference on both sides of the Ligurian Basin: the northern margin, close to the alpine chain, suffered strong earthquakes and large cumulated deformation since 5Â Ma, while the southern margin, close to the Corsica-Sardinia continental block, is poorly deformed since 5Â Ma.
Journal: Tectonophysics - Volume 676, 26 April 2016, Pages 135-147