Can Seismic Waves Be Trapped inside an Inactive Fault Zone? The Case Study of Nocera Umbra, Central Italy

Rovelli, A.; Caserta, A.; Marra, Fabrizio; Ruggiero, Vittorio

doi:10.1785/0120010288

Cited by 103 publications

(80 citation statements)

References 32 publications

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“…Ben-Zion & Aki 1990;Igel et al 1997Hillers et al 2014). These phases have been observed in various fault and geologic settings in California (Li et al 1994;Peng et al 2003;Lewis & Ben-Zion 2010) including the SJFZ (Li & Vernon 2001;Lewis et al 2005;Qiu et al 2017), Turkey , Italy (Rovelli et al 2002;Calderoni et al 2012;Avallone et al 2014), Japan (Mizuno & Nishigami 2006) and New Zealand (Eccles et al 2015).…”

Section: Methodsmentioning

confidence: 95%

Internal structure of the San Jacinto fault zone at Blackburn Saddle from seismic data of a linear array

Ben‐Zion

Ross

et al. 2017

Geophysical Journal International

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S U M M A R YLocal and teleseismic earthquake waveforms recorded by a 180-m-long linear array (BB) with seven seismometers crossing the Clark fault of the San Jacinto fault zone northwest of Anza are used to image a deep bimaterial interface and core damage structure of the fault. Delay times of P waves across the array indicate an increase in slowness from the southwest most (BB01) to the northeast most (BB07) station. Automatic algorithms combined with visual inspection and additional analyses are used to identify local events generating fault zone head and trapped waves. The observed fault zone head waves imply that the Clark fault in the area is a sharp bimaterial interface, with lower seismic velocity on the southwest side. The moveout between the head and direct P arrivals for events within ∼40 km epicentral distance indicates an average velocity contrast across the fault over that section and the top 20 km of 3.2 per cent. A constant moveout for events beyond ∼40 km to the southeast is due to off-fault locations of these events or because the imaged deep bimaterial interface is discontinuous or ends at that distance. The lack of head waves from events beyond ∼20 km to the northwest is associated with structural complexity near the Hemet stepover. Events located in a broad region generate fault zone trapped waves at stations BB04-BB07. Waveform inversions indicate that the most likely parameters of the trapping structure are width of ∼200 m, S velocity reduction of 30-40 per cent with respect to the bounding blocks, Q value of 10-20 and depth of ∼3.5 km. The trapping structure and zone with largest slowness are on the northeast side of the fault. The observed sense of velocity contrast and asymmetric damage across the fault suggest preferred rupture direction of earthquakes to the northwest. This inference is consistent with results of other geological and seismological studies.

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Section: Methodsmentioning

confidence: 95%

Internal structure of the San Jacinto fault zone at Blackburn Saddle from seismic data of a linear array

Ben‐Zion

Ross

et al. 2017

Geophysical Journal International

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“…Earthquake waveforms (Figure 2) rather show a continuous, persistent increment of high-frequency amplitudes along the entire seismogram. Also, polarized motions are not parallel to the fault strike as it would be expected for fault-guided waves that are composed of surface waves channeled in the waveguide [Rovelli et al, 2002;Lewis et al, 2005].…”

Section: Discussionmentioning

confidence: 99%

“…Many authors assert that the trapping portion of the fault is shallow, of the order of 3 km or less , in the Karadere-Düzce branch of the North Anatolian fault; Michael and Ben-Zion [1998], in the Parkfield segment of the San Andreas fault; Peng et al [2003], in the rupture zone of the Landers earthquake; Lewis et al [2005], in the San Jacinto fault zone near Anza, California; and Rovelli et al [2002], in a dormant fault near Nocera Umbra, central Italy). They all interpret the shallow trapping portion of the fault as the top part of tectonic structures of regional extent that produce a broad (100 to 200 m) zone of damaged rock.…”

Section: Discussionmentioning

confidence: 99%

“…They also observed a predominance of fault-parallel motion in the fault zone. Rovelli et al [2002] used the fault-guided waveforms of a vertically incident subcrustal earthquake to constrain depth and velocity contrast of the Nocera Umbra fault zone. Also for this fault the conclusion was that polarization of horizontal motion was parallel to the fault strike and the trapping portion of that fault was shallow (1 -1.5 km).…”

Section: Introductionmentioning

confidence: 99%

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Evidence for ground motion polarization on fault zones of Mount Etna volcano

et al. 2008

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[1] During local and regional earthquakes, an evident amplification of horizontal ground motion is observed at two seismological stations near the Tremestieri fault, on the southeastern flank of Mount Etna volcano. Rotated component spectral ratios show a narrow spectral peak around 4 Hz along a N40°E direction. A conventional polarization analysis using the eigenvectors of the covariance matrix confirms the very stable directional effect enhancing the approximately NE-SW elongation of the horizontal ground motion in the fault zone. The effect is evident during the entire seismogram and independent of source back azimuth as well as distance and depth of earthquakes. The same polarization is observed in ambient noise as well. This consistency allowed us to use microtremors for checking ground motion polarization along and across the Tremestieri fault zone with a high spatial resolution. The result is a stable polarization of horizontal motion in the entire area that can be observed in a broad frequency band. To check whether this ground motion property is recurrent and to understand a possible relationship with fault strike, faulting style, or orientation of fractures, ambient noise was recorded on other mapped faults of the Mount Etna area, the Moscarello, Acicatena, and Pernicana faults. The latter, in particular, is characterized by different strike and faulting style. A systematic tendency of ambient noise to be polarized is found in all of the faults. A picture emerges where normal faults of the eastern flank show an E-W to NE-SW polarization that changes on the Pernicana fault, which develops approximately E-W and is characterized by a prevailing NW-SE to N-S polarization. Directions of polarization were never parallel to the fault strike. Moreover, polarization persists too far away from the fault trace, excluding an effect limited to a narrow low-velocity zone hosted between harder wall rocks. Both these observations rule out an interpretation in terms of faulttrapped waves. The cause of observed polarizations will be the subject of future studies. However, the consistency with recent results of velocity anisotropy in a part of the investigated area suggests a possible role of attenuation anisotropy on horizontal amplitude variations versus azimuth.

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“…The design matrix used to compute the covariance matrix is the Jacobian matrix derived from equation (1) installed at the Nocera Umbra (Central Italy) station. The site response of Nocera Umbra station has been deeply investigated by previous studies demonstrating that large amplifications occur around 6 Hz (e.g., Rovelli et al, 2002;Castro et al, 2004;Luzi et al, 2005). For this reasons the amplitude of coefficient s 5 as a function of period, shown in In order to assess the effect of including classes D and E on the median model, the regression was also performed removing the records relative to these two classes.…”

Section: Determination Of the Coefficientsmentioning

confidence: 99%

Ground motion prediction equations derived from the Italian strong motion database

Bindi

Pacor

Luzi

et al. 2011

Bull Earthquake Eng

335

263

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We present a set of ground motion prediction equations (GMPEs) derived for the geometrical mean of the horizontal components and the vertical, considering the latest release of the strong motion database for Italy. The regressions are performed over the magnitude range 4 -6.9 and considering distances up to 200 km. The equations are derived for peak ground acceleration (PGA), peak ground velocity (PGV) and 5%-damped spectral acceleration at periods between 0.04 and 2 s. The total standard deviation (sigma) varies between 0.34 and 0.38 log 10 unit, confirming the large variability of ground shaking parameters when regional data sets containing small to moderate magnitude events (M < 6) are used. The between-stations variability provides the largest values for periods shorter than 0.2 s while, for longer periods, the between-events and between-stations distributions of error provide similar contribution to the total variability.

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Can Seismic Waves Be Trapped inside an Inactive Fault Zone? The Case Study of Nocera Umbra, Central Italy

Cited by 103 publications

References 32 publications

Internal structure of the San Jacinto fault zone at Blackburn Saddle from seismic data of a linear array

Internal structure of the San Jacinto fault zone at Blackburn Saddle from seismic data of a linear array

Evidence for ground motion polarization on fault zones of Mount Etna volcano

Ground motion prediction equations derived from the Italian strong motion database

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