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| Titel |
The long-term seismic cycle in geodynamic, numerical simulations of a subduction zone |
| VerfasserIn |
Ylona van Dinther, Taras V. Gerya, Luis A. Dalguer, P. Martin Mai, Gabriele Morra |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250054441
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| Zusammenfassung |
| Earthquakes occur over different spatial and temporal scales. While abundant data are
available to gain understanding of short-term behavior of earthquakes, the long-term
evolution of subduction zone seismicity remains elusive due to the limited observational
time span. Additional complexities of subduction zone seismicity arise from its
inaccessibility, complex setting, and the uncertainty about the nature of the thrust fault
interface. Realistic numerical modeling of subduction zone physics can help to
improve our understanding of the long-term seismic cycle. By means of quantification
of macroscopic parameters comparable to seismic observations and periodicity
through time we aim to increase our comprehension of this long-term cycle and
the physics governing it. The main challenge will be to unravel the source of this
periodicity, and see how different friction laws operating on the thrust fault affect
it.
We use a plane-strain, coupled petrological and thermo-mechanical finite-difference scheme
with marker-in-cell technique to solve the conservation of momentum, mass, and energy for a
visco-elasto-plastic rheology (I2ELVIS). In a 1500x200 km2 model a generic oceanic plate
subducts below a continental overriding plate, spontaneously generating localizations of
plastic strain when the second invariant of the deviatoric stress tensor exceeds the
Drucker-Prager yield stress.
The fluid-dynamic continuum models show several spontaneously formed clusters of plastic
strain localizations whose activity is coupled through the thrust interface. The link, in terms
of type and degree of correlation, between these clusters and their periodicity varies with
different subduction regimes, which are most likely distinguished by thrust coupling. We
observe long-term periodicities varying between either 20.000 and 40.000, and 100.000
years. Within the localization zones, we observe sudden drops in stress simultaneously with
strong increases in strain rate, i.e. a rapid spatial increase in acceleration, that we use to
define slipping events. Preliminary results from an event detection algorithm show a
heterogeneous distribution of slip within the weakest basaltic crustal layer, where the high
slip patches, i.e. asperities, are located at its thinnest, most coupled section. Also the main
seismogenic zone is located at the most coupled portion of the interface, where
events occasionally extend upward to below the accretionary wedge reaching slip
lengths up to 45 km. The seismogenic zone is roughly bounded by the 200 and 450
degrees Celsius isotherms. Preliminary we observe that a distribution of events
over a period of 200.000 years follows a power law, partially with a slope of 1.
In order to be able to draw conclusions on these patterns, we need to identify the
source of the periodicities and patterns observed and understand the physics behind
it. |
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