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| Titel |
Dealing with completeness, structural hierarchy, and seismic coupling issues: three major challenges for #Fault2SHA |
| VerfasserIn |
Gianluca Valensise, Salvatore Barba, Roberto Basili, Lorenzo Bonini, Pierfrancesco Burrato, Michele Carafa, Vanja Kastelic, Umberto Fracassi, Francesco Emanuele Maesano, Gabriele Tarabusi, Mara Monica Tiberti, Paola Vannoli |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250133593
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| Publikation (Nr.) |
 EGU/EGU2016-14222.pdf |
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| Zusammenfassung |
| The vast majority of active faulting studies are performed at the scale of individual,
presumably seismogenic faults or fault strands. Most SHA approaches and models, however,
require homogeneus information on potential earthquake sources over the entire tectonic
domain encompassing the site(s) of interest. Although it is out of question that accurate SHA
must rely on robust investigations of individual potential earthquake sources, it is only by
gathering this information in regionally extensive databases that one can address some of the
most outstanding issues in the use of #Fault2SHA. We will briefly recall three issues that
are particularly relevant in the investigation of seismogenic faulting in southern
Europe.
A fundamental challenge is the completeness of the geologic record of active
faulting. In most tectonic environments many potential seismogenic faults are blind
or hidden, or deform the lower crust without leaving a discernible signal at the
surface, or occur offshore, or slip so slowly that nontectonic erosional-depositional
processes easily outpace their surface effects. Investigating only well-expressed faults is
scientifically rewarding but also potentially misleading as it draws attention on the least
insidious faults, leading to a potential underestimation of the regional earthquake
potential.
A further issue concerns the hierarchy of fault systems. Most active faults do not
comprise seismogenic sources per se but are part of larger systems, and slip only in
conjunction with the master fault of each system. In the most insidious cases, only secondary
faults are expressed at the surface while the master fault lies hidden beneath them. This may
result in an overestimation of the true number of seismogenic sources that occur in each
region and in a biased identification of the characteristics of the main player in each
system.
Recent investigations of geologic and geodetic vs earthquake release budgets have
shown that the "seismic coupling", which quantifies the fraction of tectonic fault slip
that is turned into earthquake moment release, may be significantly smaller than
100%, particularly in contractional tectonic settings. Also this especially elusive
circumstance may result in an overestimation of the true earthquake potential of specific
areas.
All these circumstances are the source of fundamental epistemic uncertainties that are
extremely difficult to be dealt with standard approaches, which normally focus on
the variability of the parameters of major faults whose seismogenic nature is well
established.
In summary, the current generation of earthquake geologists should definitely make a turn
toward #Fault2SHA and contribute their data for improving current seismic hazard
models. To achieve this goal, however, they should first (a) step back from the surface
fault(s) and adopt a broader tectonic, geomorphic and three-dimensional perspective
that encompasses at least the entire fault system being investigated; (b) make a
more extensive use of subsurface evidence, focusing on the nature and geometry of
depositional bodies rather than simply on brittle faulting; and (c) broaden their own
perspective of the seismic cycle, comparing the (often incomplete) geological and
geomorphic evidence with the (similarly incomplete) seismicity and geodetic records. |
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