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| Titel |
Microearthquake Fracture Properties and Fluid-Driven Lubrication Processes Along a Complex Normal Fault System in Southern Apennines, Italy |
| VerfasserIn |
Antonella Orefice, Aldo Zollo, Vincenzo Convertito |
| 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 |
250079168
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| Zusammenfassung |
| We analyzed the P- and S-wave displacement spectra of 700 microearthquakes in the moment
range 4Ã109 - 2Ã1014 Nm and recorded at the dense, wide-dynamic range, seismic
networks operating in southern Apennines (Italy). Source parameters are estimated by a
parametric modeling approach which is combined with a multi-step, non-linear inversion
strategy.
In the analyzed frequency range (0.4-50 Hz), statistical tests show that the constant-Q,
attenuation model has to preferred to frequency dependent Q-models, both for P- and
S-waves. Consistent estimates of the attenuation parameter t*=T/Q are obtained from the
spectral decay of small earthquakes below the corner frequency and from the inversion of
displacement spectra of relatively larger magnitude events.
A crustal QS higher than Qp and a Qs/Qp greater than 1 is found in the same depth range
where high Vp/Vs and a peak in seismicity distribution are observed. This is the evidence for
a highly fractured, partially fluid-saturated medium embedding the Irpinia fault zone, down to
crustal depths of 15-20 km.
A nearly constant stress drop (8.3 MPa) and apparent stress (3.1 MPa) scaling of P- and
S-corner frequencies and seismic energies is observed above a seismic moment value
of about 1011 Nm. Below this value the corner frequencies and seismic energy
are not measurable, due to the instrument band-limitation and noise effect at high
frequencies.
The ratio between apparent stress and static stress drop (Savage-Wood seismic efficiency)
is relatively high (0.5), indicating that the radiated energy is a very large fraction of the sum
of energies spent by friction and fracture development. It remains approximately constant
over about four orders of magnitude, indicating that apparent stress and static stress drop
co-varies, independently on the fracture size, at least in the explored magnitude
range.
Seismic efficiency appears to be higher in the same depth range where high
Vp/Vs and Qs/Qp values are also observed. This suggests that dynamic weakening
driven by crustal fluid pressurization is the most plausible mechanism controlling
the seismic radiation from microearthquake ruptures along the studied fault zone. |
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