Publication Date:
2017-04-04
Description:
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.
Description:
INGV
Description:
Published
Description:
B07303
Description:
3.1. Fisica dei terremoti
Description:
JCR Journal
Description:
reserved
Keywords:
Cupper crustal structure
;
fault zones evolution
;
pore pressure variation
;
temporal variation of elastic properties
;
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
Permalink
