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| Titel |
Crustal structure, seismicity and seismotectonics of the Trentino region (Southern Alps, Italy) |
| VerfasserIn |
Alfio Vigano, Davide Scafidi, Silvana Martin, Daniele Spallarossa, Luca Froner, Oscar Groaz |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250079039
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| Zusammenfassung |
| The Trentino region is located at the junction between the central and eastern Southern Alps
(Italy), at the intersection between the Giudicarie, Schio-Vicenza and Valsugana fault
systems. This area is characterized by relevant lithological and structural lateral
heterogeneities, both at the crustal and lithospheric scales. A low-to-moderate seismicity is
located in the upper crust, where faults are seismically active under a dominant compressive
with variable strike-slip component regime. Here we study the crustal structure of this portion
of the Southern Alps (Adria plate) from interpretation of local earthquake tomography
images, in relation with distribution of relocated seismicity and regional tectonic
patterns.
Local earthquake tomography derives from a set of 476 selected earthquakes in the period
1994-2007, with local magnitudes comprised between 0.8 and 5.3. Hypocenter distribution,
and number and quality of manually-repicked phases (6322 P and 5483 S) ensure optimal
seismic ray coverage. Original recordings are principally from the Provincia Autonoma di
Trento (PAT), that manages the Trentino seismic network since 1981, and from other
networks (Istituto Nazionale di Oceanografia e di Geofisica Sperimentale – INOGS; Istituto
Nazionale di Geofisica e Vulcanologia – INGV; others available via the European Integrated
Data Archive). The code HYPOELLIPSE is used to perform initial earthquake relocations.
The code VELEST is then used to calculate a new minimum 1-D velocity model, as input for
tomography.
The 3-D tomographic inversion (V P and V P-V S ratio) is obtained via the code
SIMULPS, with the implementation of an accurate shooting ray-tracer. The crustal volume is
discretized in order to have a regular grid with a homogenous horizontal spatial resolution of
7.5 km. The resolution in depth varies according to the obtained minimum 1-D
velocity model. Reliability and accuracy of results are estimated by analyzing the
Resolution Diagonal Elements of the resolution matrix and by checkerboard resolution
tests.
The distribution of velocity anomalies from tomographic images within the
investigated crustal volume shows very good correlations with surface geology and
geodynamics. Strong lateral velocity anomalies of the crust are interpreted as due
to lithological variations corresponding to different geologic domains (carbonate
cover, magmatism, metamorphic basements). V P-V S ratios are also significantly
variable, with highest values in the range 1.80–1.90 located along major faults
(South Giudicarie and Valsugana-Bassano del Grappa-Montello thrusts). These
values are interpreted as due to high fracturing and/or presence of fluids in the upper
crust.
The obtained 3-D tomographic velocity model is used to relocate not only best-quality
earthquakes used as input for tomographic inversion, but also those with an adequate
number and quality of phase readings during the same time period. For this purpose
we use the code NonLinLoc, with specifically calibrated parameters for the study
area. A significant quality improvement in hypocentral solutions can be obtained
locating earthquakes using the 3-D V P and V S velocity model, rather than a more
simplified 1-D velocity model. This procedure represents a critical step to enable
high-quality local seismic event (re)locations in the Trentino region (e.g., seismic
bulletin), also to perform more reliable seismic hazard maps for civil protection. |
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