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| Titel |
Broadband Near-Field Ground Motion Simulations in 3D Scattering Media |
| VerfasserIn |
Walter Imperatori, Martin Mai |
| 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 |
250079856
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| Zusammenfassung |
| The heterogeneous nature of Earth’s crust is manifested in the scattering of propagating
seismic waves. In recent years, different techniques have been developed to include such
phenomenon in broadband ground-motion calculations, either considering scattering as a
semi-stochastic or pure stochastic process. In this study, we simulate broadband (0-10 Hz)
ground motions using a 3D finite-difference wave propagation solver using several 3D media
characterized by Von Karman correlation functions with different correlation lengths and
standard deviation values. Our goal is to investigate scattering characteristics and its influence
on the seismic wave-field at short and intermediate distances from the source in terms of
ground motion parameters. We also examine other relevant scattering-related phenomena,
such as the loss of radiation pattern and the directivity breakdown. We first simulate
broadband ground motions for a point-source characterized by a classic omega-squared
spectrum model. Fault finiteness is then introduced by means of a Haskell-type source
model presenting both sub-shear and super-shear rupture speed. Results indicate that
scattering plays an important role in ground motion even at short distances from the
source, where source effects are thought to be dominating. In particular, peak ground
motion parameters can be affected even at relatively low frequencies, implying
that earthquake ground-motion simulations should include scattering also for PGV
calculations. At the same time, we find a gradual loss of the source signature in the 2-5 Hz
frequency range, together with a distortion of the Mach cones in case of super-shear
rupture. For more complex source models and truly heterogeneous Earth, these effects
may occur even at lower frequencies. Our simulations suggest that Von Karman
correlation functions with correlation length between several hundred meters and few
kilometers, Hurst exponent around 0.3 and standard deviation in the 5-10% range
reproduce the available observations, although an unambiguous random-media
characterization of the Earth crust in the distance range currently cannot be achieved |
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