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R. Giuliani M. Anzidei L. Bonci S. Calcaterra N. D'Agostino M. Mattone G. Pietrantonio F. Riguzzi G. Selvaggi 《Tectonophysics》2007,432(1-4):21-35
The 2002 earthquake sequence of October 31 and November 1 (main shocks Mw = 5.7) struck an area of the Molise region in Southern Italy. In this paper we analyzed the co-seismic deformation related to the Molise seismic sequence, inferred from GPS data collected before and after the earthquake, that ruptured a rather deep portion of crust releasing a moderate amount of seismic energy with no surface rupture. The GPS data have been reduced using two different processing strategies and softwares (Bernese and GIPSY) to have an increased control over the result accuracy, since the expected surface displacements induced by the Molise earthquake are in the order of the GPS reliability. The surface deformations obtained from the two approaches are statistically equivalent and show a displacement field consistent with the expected deformation mechanism and with no rupture at the surface. In order to relate this observation with the seismic source, an elastic modeling of fault dislocation rupture has been performed using seismological parameters as constraints to the model input and comparing calculated surface displacements with the observed ones. The sum of the seismic moments (8.9 × 1017 Nm) of the two main events have been used as a constraint for the size and amount of slip on the model fault while its geometry has been constrained using the focal mechanisms and aftershocks locations. Since the two main shocks exhibit the same fault parameters (strike of the plane, dip and co-seismic slip), we modelled a single square fault, size of 15 km × 15 km, assumed to accommodate the whole rupture of both events of the seismic sequence. A vertical E–W trending fault (strike = 266°) has been modeled, with a horizontal slip of 120 mm. Sensitivity tests have been performed to infer the slip distribution at depth. The comparison between GPS observations and displacement vectors predicted by the dislocation model is consistent with a source fault placed between 5 and 20 km of depth with a constant pure right-lateral strike-slip in agreement with fault slip distribution analyses using seismological information. The GPS strain field obtained doesn't require a geodetic moment release larger than the one inferred from the seismological information ruling out significant post-seismic deformation or geodetic deformation released at frequencies not detectable by seismic instruments. The Molise sequence has a critical seismotectonic significance because it occurred in an area where no historical seismicity or seismogenic faults are reported. The focal location of the sequence and the strike-slip kinematics of main shocks allow to distinguish it from the shallower and extensional seismicity of the southern Apennines being more likely related to the decoupling of the southern Adriatic block from the northern one. 相似文献
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The 2002 Molise earthquake sequence: What can we learn about the tectonics of southern Italy? 总被引：1，自引：3，他引：1
On October 31, 2002 a ML = 5.4 earthquake occurred in southern Italy, at the margin between the Apenninic thrust belt (to the west) and the Adriatic plate (to the east). In this area, neither historical event nor seismogenic fault is reported in the literature. In spite of its moderate magnitude, the earthquake caused severe damage in cities close to the epicenter and 27 people, out of a total of 29 casualties, were killed by the collapse of a primary school in S. Giuliano di Puglia. By inverting broadband regional waveforms, we computed moment tensor solutions for 15 events, as small as ML = 3.5 (Mw = 3.7). The obtained focal mechanisms show pure strike-slip geometry, mainly with focal planes oriented to NS (sinistral) and EW (dextral). In several solutions focal planes are rotated counterclockwise, in particular for later events, occurring west of the mainshock. From the relocated aftershock distribution, we found that the mainshock ruptured along an EW plane, and the fault mechanisms of some aftershocks were not consistent with the mainshock fault plane. The observed stress field, resulting from the stress tensor inversion, shows a maximum principal stress axis with an east–west trend (N83°W), whereas the minimum stress direction is almost N–S. Considering both the aftershock distribution and moment tensor solutions, it appears that several pre-existing faults were activated rather than a single planar fault associated with the mainshock. The finite fault analysis shows a very simple slip distribution with a slow rupture velocity of 1.1 km/s, that could explain the occurrence of a second mainshock about 30 h after. Finally, we attempt to interpret how the Molise sequence is related to the normal faulting system to the west (along the Apennines) and the dextral strike-slip Mattinata fault to the east. 相似文献
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The 1627 Gargano earthquake (Southern Italy): Identification and characterization of the causative fault 总被引：4，自引：0，他引：4
We present the results of a study of the subsurface tectonic features of the Basso Molise, Western Gargano and Northern Capitanata regions (Southern Italy) aimed at the identification of the source of the disastrous 1627 Gargano earthquake. In the maximum-damage area of this earthquake we have recognised a normal fault, here called the Apricena Fault, which has been identified as the fault that caused the seismic event. The Apricena Fault, striking WNW-ESE and dipping towards SSW, extends in the subsurface for about 30 kilometres from Serracapriola to Santa Maria di Stignano cutting through the whole Quaternary sequence. Other important tectonic structures trending WNW-ESE recognized in the area belong to an inactive Pleistocene strike-slip-fault system that is linked to the Mattinata Fault and to its offshore continuation in the Gondola-Grifone structural high. The Mattinata Fault and the Gondola-Grifone High form a quite complex structural feature whose kinematic behaviour is still matter of debate in the regional geological literature. NW-SE structural features recognized in the area are extensional faults whose activity was probably related to the late flexure-hinge retreat of the Adria plate margin during the Late Pliocene-Early Pleistocene eastward migration of the thrust belt-foredeep-foreland system. 相似文献
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A. Strollo S. M. Richwalski S. Parolai M. R. Gallipoli M. Mucciarelli R. Caputo 《Bulletin of Earthquake Engineering》2007,5(3):347-362
On 31 October and 1 November 2002, the Basso Molise area (Southern Italy) was struck by two earthquakes of moderate magnitude
(M
L = 5.4 and 5.3). The epicentral area showed a high level of damage, attributable both to the high vulnerability of existing
buildings and to site effects caused by the geological and geomorphological settings. Specifically, the intensity inside the
town of San Giuliano di Puglia was two degrees higher than in neighbouring towns. Also, within San Giuliano di Puglia, the
damage varied notably. The site response in the city was initially evaluated from horizontal-to-vertical spectral ratios (HVSR)
from a limited number of strong motion recordings of the most severe aftershocks. Several microtremor measurements were also
available. Both data sets indicated the simultaneous presence of two amplification peaks: one around 6 Hz, attributed in previous
studies to the strong, shallow impedance contrast among landfill/clay and calcarenites, and one at 2 Hz related to the first
S-wave arrivals and predominantly seen only on one receiver component. Further studies performed on weak-motion recordings
also showed strong amplification on the vertical receiver component, thus indicating an underestimation of the amplification
by the HVSR technique. Additionally, a 2D-model of the geology of the sub-surface was developed, reproducing the flower-shaped
structure generated during the late orogenic transpressive regime. The numerical (finite-difference hybrid) simulation reproduced
the two peaks of the observed data at slightly higher frequencies. The model also confirmed that the borders of the flower
structure define a boundary between amplification levels, with higher amplification inside. 相似文献
5.
On 31 October and 1 November 2002, two earthquakes took place in the Italian region of Molise. 29 deaths were reported, while
many buildings collapsed or suffered major damage. The tectonics of the earthquakes and historic seismicity of the area are
briefly described. The distribution of damage and macroseismic intensity are confronted with the current seismic zonation
of the region. In particular, the paper deals with the damage suffered by different types of structures, namely masonry and
RC buildings and historical churches. The observed damage is mainly attributed to the poor quality of the materials and execution
of construction, lack of maintenance and protective devices (e.g., steel ties), as well as to structural interventions. Reference
is made to the management of the post-earthquake emergency.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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