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| Titel |
Focal Mechanism Determination of Induced Microearthquakes in an Oil Field Using Full Waveforms from Shallow and Deep Monitoring Networks |
| VerfasserIn |
Junlun Li, H. Sadi Kuleli, Haijiang Zhang, M. Nafi Toksoz |
| 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 |
250056855
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| Zusammenfassung |
| We present a new method using high frequency full waveform information to determine the
focal mechanisms of small, local earthquakes monitored by a sparse surface network and a
deep borehole network in a petroleum field. During the waveform inversion, we maximize
both the phase and amplitude matching between the observed and modeled waveforms. In
addition, we use the polarities of the first P-wave arrivals and the average S/P amplitude ratios
to better constrain the matching. An objective function is constructed to include all four
criteria. An optimized grid search method is used to search over all possible ranges of source
parameters (strike, dip and rake). To speed up the algorithm, a library of Green’s
functions is pre-calculated for each of the moment tensor components and possible
earthquake locations using the Discrete Wavenumber Method based on the 1-D
layered medium from the sonic logs and traveltime tomography results. Optimizations
in filtering and cross-correlation are performed to further speed the grid search
algorithm.
For the surface network, we first performed a comprehensive synthetic test including 27
synthetic events. The synthetic test shows that our method is robust and efficient even with
inaccurate velocity models (~10% random perturbation) for different hypocenters
and source types using only the vertical component of seismograms. Waveforms
between 3-9 Hz are used to determine the focal mechanisms of induced seismicity
(-0.50< Mw |
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