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| Titel |
Quantifying Fault Slip Rate Variations and Earthquake Clustering |
| VerfasserIn |
Patience Cowie, Gerald Roberts, Richard Phillips |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250037897
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| Zusammenfassung |
| An outstanding challenge to our understanding of fault behaviour remains the appropriate
characterisation and mechanistic understanding of episodic fault activity and temporal
variations in slip rate. This gap in understanding inhibits our ability to reconcile geodetic and
geologic strain rates and hence predict future earthquakes. Existing models for earthquake
recurrence and seismic hazard are based on the key principle that a mean recurrence interval,
Tmeancan be defined. For areas of active crustal deformation where there are several active
faults, and/or the regional strain rate is relatively low, historical earthquake catalogues are
unable to provide adequate constraints on Tmean because the earthquake cycle of some faults
is longer than the catalogue itself. Paleoseismological trench studies have extended
the window of observation back for a few thousand years and suggest that large
temporal variability in recurrence interval occurs on individual faults. Current practice
in seismic hazard analysis is to characterise variability in recurrence interval by
defining the Coefficient of Variation (CV) for a sequence of earthquakes where
CV = Ï/ Tmean, and Ï is the standard deviation of the inter-event times. Several
studies acknowledge that CV values for earthquake recurrence intervals are poorly
constrained yet small differences in CV can lead to order of magnitude difference in
conditional probability calculations. We use a numerical fault growth model, which
includes earthquake rupture, healing and elastic interaction, to investigate the controls
on CV, both spatially across the fault array and through time as the fault pattern
evolves. We find that CV varies inversely with fault slip rate, which itself varies as a
function of fault zone complexity, i.e., when the strain is partitioned on more than one
structure CV increases. However, we also find that CV is not the most informative
parameter to measure in our model output. Firstly, it only takes into account earthquake
recurrence interval and not the temporal sequence and magnitudes of the fault offsets.
Secondly, robust estimates of CV require a complete inventory of a large number
of events (>10), which is unlikely to be available for real faults, thus rendering
the comparison with natural data sets difficult. From the analysis of our model
output, we conclude that slip rate variability SRV = (standard deviation of slip
rate over a fixed time window)÷(long term average slip rate), provides a more
robust and sensitive measure of spatial and temporal variations in fault behaviour. In
particular, SRV is relatively insensitive to the completeness of the record for smaller
magnitude offsets while being highly sensitive to the time order and magnitude
of larger magnitude offsets. We investigate how SRV varies as a function of fault
geometry, i.e., spacing, orientation and structural complexity, and compare our
model results with field data on fault activity from the central Apennines of Italy. |
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