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Ben-Zion, Yehuda
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- PublicationOpen AccessSeismicity Patterns on Fault Zones with Different Geometrical and Rheological Properties(2007-05-31)
; ;Ben-Zion, Y.; Department of Earth Sciences, University of Southern California, CA, USA; ; ; ; ;Cocco, Massimo; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Console, Rodolfo; INGV, Rome, Italy ;Wiemer, Stefan; ETH, Zurich, Switzerland; ; Seismicity Patterns on Fault Zones with Different Geometrical and Rheological Properties99 170 - PublicationOpen AccessGROUND MOTION POLARIZATION IN FAULT ZONES : RELATION WITH BRITTLE DEFORMATION FIELDS(2010-12-13)
; ; ; ; ;Pischiutta, Marta; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Rovelli, Antonio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Fle, Jon B.; USGS Menlo Park (CA) ;Salvini, Francesco; Roma Tre University ;Ben-Zion, Yehuda; University of Southern California, Los Angeles (CA); ; ; ; ; ; ;Pischiutta, Marta; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, ItaliaSeveral recent studies indicate that ambient noise and seismic signals in fault zones tend to be polarized on the horizontal plane with a clear preferred orientation direction. Here we present a summary of past experiments as well as new study cases showing evidence of this effect: the Val d’Agri, the Pernicana and the Paganica faults in Italy, and the Hayward fault in California. We also analyze data recorded by the HRSN network at the Parkfield section of the San Andreas fault and find that stations MM and GH that are close to the fault damage zone show a similar persistent and marked polarization effect. The approach combines the H/V technique in the frequency domain with the covariance matrix diagonalization method in the time domain. Common features are: i) a high stability of results at each site, independently of the nature and location of the source of seismic signals, ii) a characteristic polarization for each fault, and iii) the preferred polarization is close to the fault-normal direction, rather than being fault parallel as would be expected for generation of fault zone trapped waves. In previous papers, the role of fluid-filled microcracks in the damage zone was hypothesized. We have then explored an hypothesis based on the fracture field orientation in the fault damage zone by applying the package FRAP3 (Salvini, 2002) to model the brittle deformation field expected for the studied faults. We have found a consistent orthogonal relation between the observed polarizations and the orientation of the predicted synthetic fracture systems. When anisotropy studies are available, the horizontal ground motion polarization is consistently found to be perpendicular to the fast wave splitting component. The results may reflect reduced stiffness in the fault-normal direction produced by the presence of damage fault zone rocks.141 113 - PublicationOpen AccessScaling relations of earthquakes, aseismic deformation and evolving fault structures in a damage rheology model(2007-09-25)
; ; ;Lyakhovsky, V.; Geological Survey, Israel ;Ben-Zion, Y.; Univ. of Southern California, USA; ; ; ; ;Vinciguerra, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Bernabé, Y.see Abstract Volume84 108 - PublicationRestrictedWave-guide effects in very high rate GPS record of the 6 April 2009, Mw 6.1 L'Aquila, central Italy earthquake(2014-01-21)
; ; ; ; ; ; ; ;Avallone, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Rovelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Di Giulio, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Improta, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Ben-Zion, Y.; University of Southern California ;Milana, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Cara, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; ; ; ; ; A 10 Hz sampling frequency GPS station was installed near L'Aquila a few days before the 6 April 2009 Mw 6.1 earthquake. It recorded displacement waveforms during the main shock and the largest Mw 5.4 aftershock of 7 April. The horizontal components of the main shock contain a high-amplitude (43 cm peak-to-peak) nearly harmonic (1 Hz) wave train not evident in other nearby instrumental records. The persistency of this feature during aftershocks recorded by a temporarily colocated seismological station highlights a local site effect. Traditional models based on near-surface velocity structure and topography variations fail to reproduce the size and frequency band of the observed amplified motion. The amplified wave train can be explained by a low-velocity fault zone layer below the station. This model fits the delay of the large-amplitude nearly harmonic wave train after the S wave phase and is consistent with the variation in the fault excitation efficiency between the two shocks in relation to their different source depth and location. Synthetic calculation of trapped waves in a model consisting of two quarter spaces separated by a 650 m wide low-velocity zone with 50% velocity reduction and Q value of 20 fit well the observed anomalous record. The parameters of the model fault zone layer are consistent with geological evidence of a broad damage zone adjacent to the station and a similar site response found in this crustal zone with ambient noise. Results of shallow seismic surveys and sonic logs from deep wells provide independent constraints on the host rock velocities.786 86 - PublicationRestrictedDirectional resonance variations across the Pernicana Fault, Mt Etna, in relation to brittle deformation fields(2013-01-24)
; ; ; ; ; ;Pischiutta, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Rovelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Salvini, F.; Department of Earth Sciences, Universit`a RomaTre, Rome, Italy ;Di Giulio, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Ben-Zion, Y.; Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA; ; ; ; The Pernicana Fault (PF) is the main structural element of Mt Etna and the northern boundary of a section sliding to the southeast. Observed ground motion records in the damage zone of the PF show strong variations of directional resonance in the horizontal plane. The observed resonance directions exhibit an abrupt rotation of azimuth by about 30◦ across the fault, varying from N166◦ on the north side to N139◦ on the south. We interpret the directional resonance observations in terms of changes in the kinematics and deformation fields on the opposite sides of the fault. The northern side is affected primarily by the left-lateral strike-slip movement, whereas the southern side, that is subjected also to sliding, is under a dominant extensional stress regime. Brittle deformation models based on the observed kinematic field predict different sets of fractures on the opposite sides of the fault: synthetic cleavages and extensional fractures are expected to dominate in the northern and southern sides, respectively. These two fracture fields have different orientations (N74◦ and N42◦, respectively) and both show a near-orthogonal relation (∼88◦ in the northern sector and ∼83◦ to the south) with the azimuth of the observed directional resonance. We conclude that the direction of the largest resonance motions is sensitive to and has transversal relationship with the dominant fracture orientation. The directional amplification is inferred to be produced by stiffness anisotropy of the fault damage zone, with larger seismic motions normal to the fractures.343 28 - PublicationOpen AccessHorizontal polarization of ground motion in the Hayward fault zone(2012)
; ; ; ; ; ;Pischiutta, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Salvini, F.; Roma Tre University ;Fletcher, J. B.; USGS Menlo Park (CA) ;Rovelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Ben-Zion, Y.; University of Southern California, Los Angeles (CA); ; ; ; We investigate shear wave polarization in the Hayward fault zone near Niles Canyon, Fremont, CA. Waveforms of 12 earthquakes recorded by a seven-accelerometer seismic array around the fault are analysed to clarify directional site effects in the fault damage zone. The analysis is performed in the frequency domain through H/V spectral ratios with horizontal components rotated from 0◦ to 180◦, and in the time domain using the eigenvectors and eigenvalues of the covariance matrix method employing three component records. The near-fault ground motion tends to be polarized in the horizontal plane. At two on-fault stations where the local strike is N160◦, ground motion polarization is oriented N88 ± 19◦ and N83 ± 32◦, respectively. At a third on-fault station, the motion is more complex with horizontal polarization varying in different frequency bands. However, a polarization of N86 ± 7◦, similar to the results at the other two on-fault stations, is found in the frequency band 6–8 Hz. The predominantly high-angle polarization from the fault strike at the Hayward Fault is consistent with similar results at the Parkfield section of the San Andreas Fault and the Val d’Agri area (a Quaternary extensional basin) in Italy. In all these cases, comparisons of the observed polarization directions with models of fracture orientation based on the fault movement indicate that the dominant horizontal polarization is near-orthogonal to the orientation of the expected predominant cracking direction. The results help to develop improved connections between fault mechanics and near-fault ground motion.317 518 - PublicationOpen AccessTrapped seismic fault zone energy recorded by a high-rate GPS station(2010)
; ; ; ;Avallone, Antonio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Rovelli, Antonio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Ben-Zion, Yehuda; University of Southern California; ; The ground motion of the April 6th 2009 Mw 6.3 L'Aquila (Central Italy) earthquake, occurred on a SW-dipping normal fault, was successfully recorded by one of the GPS stations installed near L'Aquila before the seismic event and acquiring with a high sampling rate (10 Hz). These data provide valuable ground displacement time histories in the near source. GPS and strong motion data provided reliable reconstruction of the main features around the source. However, a low frequency (about 1 Hz) nearly-harmonic large oscillation (about 40 cm peak-to-peak) detected at this GPS station 5 s after the beginning of the coseismic dynamic deformation, and spanning about 6.5 s, was not possible to be fit by reliable source modeling. 1 Hz nearly-harmonic oscillations are also observed by a co-located seismological station installed one year after the mainshock. Both the GPS and the seismic stations are located on the eastern slope of the Mt. Ocre ridge, along which runs the the Monticchio-Fossa fault, a shallow and steep NE-dipping antithetic fault bordering the Aterno Valley graben. We have checked that the late large-amplitude coseismic displacement can be generated by energy trapped in this fault. We have obtained satisfactory results by using a line dislocation in a structure consisting in two quarter-spaces separated by vertical fault layers. Our best fit corresponds to a model characterized by a vertical 200 m-wide fault zone with impedance contrasts with respect to the adjacent left and right quarter-spaces of about 17% and 40%, respectively.158 377