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Upper crustal structure, seismicity and pore pressure variations in an extensional seismic belt through 3‐D and 4‐D VP and VP/VS models: The example of the Val d’Agri area (southern Italy)
Author(s)
Language
English
Obiettivo Specifico
3.1. Fisica dei terremoti
Status
Published
JCR Journal
JCR Journal
Peer review journal
Yes
Title of the book
Issue/vol(year)
/116 (2011)
Publisher
Journal of Geophysical Research
Pages (printed)
B07303
Issued date
July 15, 2011
Abstract
We use local earthquake tomography and background seismicity to investigate
static and transient features of the crustal velocity structure in the Val d’Agri (southern
Apennines, Italy), one of the regions in central Mediterranean with the highest seismogenic
potential. The upper crust is dominated by two broad high‐velocity anticlines of the buried
Apulia Carbonate Platform ramping on two parallel high‐angle thrusts interpreted as
preexisting inverted normal faults. The deep core of the anticlines consists of very high VP
(up to 6.9 km/s) and low VP/VS rocks, suggesting the involvement of the Apulian
crystalline basement in the Apennine belt. These results provide valuable constraints on
the Apennine belt tectonic evolution, supporting a thick‐skinned interpretation for the
Pliocene terminal phase of the compressional tectonics. The geometry of the Val d’Agri
Quaternary basin is controlled by these inherited compressive features, whereas the
presently active extensional tectonics barely reworked the structure. We find inconsistency
between the structure of the Apulia Carbonate Platform and the location and geometry
of the Quaternary normal faults mapped at the surface. This suggests either the immaturity
of the normal faults or their secondary role in accommodating the extension. We observe
spatiotemporal (4‐D) changes of VP and VP/VS models defining transient variations of
pore fluid pressure in the upper crust. A strong change in the VP/VS ratio heralds a raise in
the seismicity rate that can be related to large water level changes in a nearby artificial
lake. This evidence is consistent with a mechanism of reservoir‐induced seismicity by
fluid pressure increase and pore pressure diffusion. The 4‐D velocity variations are
confined in the shallow portion of the upper crust (3–6 km depth) where fluids are stored
in a highly fractured medium. Pore pressure fluctuations can affect the strength of fault
segments, favoring seismicity rate changes along the active faults and possibly promoting
large future earthquakes.
static and transient features of the crustal velocity structure in the Val d’Agri (southern
Apennines, Italy), one of the regions in central Mediterranean with the highest seismogenic
potential. The upper crust is dominated by two broad high‐velocity anticlines of the buried
Apulia Carbonate Platform ramping on two parallel high‐angle thrusts interpreted as
preexisting inverted normal faults. The deep core of the anticlines consists of very high VP
(up to 6.9 km/s) and low VP/VS rocks, suggesting the involvement of the Apulian
crystalline basement in the Apennine belt. These results provide valuable constraints on
the Apennine belt tectonic evolution, supporting a thick‐skinned interpretation for the
Pliocene terminal phase of the compressional tectonics. The geometry of the Val d’Agri
Quaternary basin is controlled by these inherited compressive features, whereas the
presently active extensional tectonics barely reworked the structure. We find inconsistency
between the structure of the Apulia Carbonate Platform and the location and geometry
of the Quaternary normal faults mapped at the surface. This suggests either the immaturity
of the normal faults or their secondary role in accommodating the extension. We observe
spatiotemporal (4‐D) changes of VP and VP/VS models defining transient variations of
pore fluid pressure in the upper crust. A strong change in the VP/VS ratio heralds a raise in
the seismicity rate that can be related to large water level changes in a nearby artificial
lake. This evidence is consistent with a mechanism of reservoir‐induced seismicity by
fluid pressure increase and pore pressure diffusion. The 4‐D velocity variations are
confined in the shallow portion of the upper crust (3–6 km depth) where fluids are stored
in a highly fractured medium. Pore pressure fluctuations can affect the strength of fault
segments, favoring seismicity rate changes along the active faults and possibly promoting
large future earthquakes.
Sponsors
INGV
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article
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