Publication Date:
2017-04-04
Description:
The Mercure earthquake (Mw 5.6) of September 9, 1998 and the associated aftershocks occurred in a small
Pleistocene–Holocene continental basin of the Southern Apennines, in a region of low instrumental and
moderate historical seismicity. Seismological, photogeological and field survey data were analyzed and
integrated in order to identify the likely seismogenic structure, to depict its 3-D geometry and kinematics and
to provide further constraints to the seismogenic potential of the rupture processes in the study area. The
mainshock occurred at the NW edge of the seismic sequence (40.03°N and 15.95°) at a depth of 10.5±
1.5 km. The aftershocks volume was determined from the relocation of about 200 events (1.1=Ml=3.9)
registered by local networks from September 10 to October 12, 1998. The relocation procedure was based on
choosing P and S waves for all the events and the definition of ten 9-layers velocity models appropriate for
the different stations. The kinematics of the seismogenic deformation was defined through the computation
of 36 well-constrained focal mechanisms. The seismological and geological stress tensors were determined
through inversion of focal mechanisms and fault slip data. Both of them resulted in the tensional type, with
ENE–WSW and NE–SW trending σ3 axis, respectively. The map and the section distribution of the
aftershocks sequence depicts an average NW–SE striking and 60° SW-dipping seismogenic volume. Most of
the events (80%) were located at depths between 3 and 8 km in the footwall of the Mercure basin (MBB)
boundary fault but along the possible down-dip continuation of a previously unidentified, N120°E striking
and WSW-dipping, Holocene normal fault alignment, which extends from Castello Seluci to Piana Perretti
and Timpa della Manca (CPST fault). A small percentage of events (10%) were located at depths between 10
and 12 km where the CPST seismogenic fault may detach.
The reconstructed rupture area (RA) of the Mercure 1998 earthquake has an along-strike length (L) of about
9 km and a down-dip width (W) of about 9 km, yielding a total area of approximately 81 km2
. On the other
hand, the L and W dimension of the entire individual seismogenic structure identified as responsible for the
earthquake, e.g. the CPST fault, are about 19 and 12 km, respectively, with a consequent RA of about 230 km2
.
This may imply a maximum magnitude (Mw) equal to 6.3 which lead us to compare the Mercure area, in
terms of seismogenic hazard, to the adjacent Pollino-Castrovillari area where strong paleoseismological
events are documented.
Description:
Published
Description:
210–225
Description:
3.2. Tettonica attiva
Description:
JCR Journal
Description:
reserved
Keywords:
Southern Apennines
;
Stress-distribution
;
Earthquake location
;
Seismotectonics
;
04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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