Enzo Boschi

Finite fault inversion of DInSAR coseismic displacement of the 2009 L’Aquila earthquake (central Italy)

[1]xa0We define the geometric and kinematic characteristics of the fault activated during the Mw = 6.3, 6 April 2009 LAquila earthquake, from the modeling of Envisat and COSMO-SkyMed (the first ever X-band interferogram inverted for a coseismic dislocation study) DInSAR interferograms. Our best-fit solution for the main shock is represented by a normal fault ∼16 km long and ∼12 km wide, with a small right-lateral component, dipping 47°SW with a maximum slip of ∼90 cm. Although the seismic dislocation probably ended at 1 km depth, the updip projection of the fault plane corresponds to the northern segment of the mapped Paganica–S. Demetrio fault, where alignment of surface breaks was observed in the field. The absence of this fault in existing seismic source catalogues suggests that an improved approach, involving detailed surface and subsurface geological and geophysical investigations, is needed for a better assessment of the seismic hazard at the local scale.

Coseismic deformation of the destructive April 6, 2009 L'Aquila earthquake (central Italy) from GPS data

[1]xa0On April 6, 2009, 01:32:39 GMT, the city of LAquila was struck by a Mw 6.3 earthquake that killed 307 people, causing severe destruction and ground cracks in a wide area around the epicenter. Four days before the main shock we augmented the existing permanent GPS network with five GPS stations of the Central Apennine Geodetic Network (CaGeoNet) bordering the LAquila basin. The maximum horizontal and vertical coseismic surface displacements detected at these stations was 10.39 ± 0.45 cm and −15.64 ± 1.55 cm, respectively. Fixing the strike direction according to focal mechanism estimates, we estimated the source geometry with a non linear inversion of the geodetic data. Our best fitting fault model is a 13 × 15.7 km2 rectangular fault, SW-dipping at 55.3 ± 1.8°, consistent with the position of observed surface ruptures. The estimated slip (495 ± 29 mm) corresponds to a 6.3 moment magnitude, in excellent agreement with seismological data.

The 2007 Stromboli eruption: Event chronology and effusion rates using thermal infrared data

Accepted for publication in Journal of Geophysical Research. Copyright (2009) American Geophysical Union. Further reproduction or electronic distribution is not permitted.

The Location and Sizing of Historical Earthquakes Using the Attenuation of Macroseismic Intensity with Distance

We herein describe new methods for computing the quantitative parameters of earthquakes using macroseismic data and the uncertainties associated with these parameters. The methods allow for the location of epicenters that are offshore or that have no intensities assigned to any points in the epicentral region by maximizing the likelihood function of an attenuation equation with observed intensity data. In the most favorable cases, such an approach also allows the estimation of the source depth and the local attenuation coefficients. We compute the parameter uncertainties in two ways: (1)xa0using formal methods, such as the inversion of the Hessian of the log-likelihood function at its maximum, and (2)xa0by using bootstrap simulations. We tested the performance of our methods by comparison with reliable instrumental hypocenters of onshore earthquakes, and found a reasonable agreement with the epicentral locations (within 10–15xa0km for more than 70% of cases) but not with the hypocentral depths, for which our results are generally underestimated by a factor of 2 or more and are poorly related to instrumental estimates. This finding indicates that the use of macroseismic depths in seismic hazard and seismotectonic investigations should be treated with caution. We nevertheless found good agreement (within 10°–15°) between the fault-trace orientations that were computed using the macroseismic data and the associated focal mechanisms of earthquakes with M w≥5.7. The surprising accuracy of the macroseismic orientations obtained using this method could in some cases allow the true fault to be inferred between the two conjugate planes of a given focal mechanism.

A multiparameter approach to volcano monitoring based on 4D analyses of seismo-volcanic and acoustic signals: The 2008 Mt. Etna eruption

[1]xa0Volcanic tremor and low frequency events, together with infrasound signals, can represent important precursory phenomena of eruptive activity because of their strict relationship with eruptive mechanisms and with fluid flows through the volcanos feeding system. Important variations of these seismo-volcanic and infrasound signals, recorded at Mt. Etna volcano, occurred both in the medium- and short-term before the eruption, that took place on 13 May 2008. The most significant changes were observed in the frequency content and location of LP events, as well as in volcanic tremor location, that allowed us to track the magma pathway feeding the 2008 eruptive activity. The infrasound showed three different families of events linked to the activity of the three active vents: North-East Crater, South-East crater and the eruptive fissure. The seismic and infrasonic variations reported, corroborated by ground deformations variations, help to develop a quantitative prediction and early-warning system for effusive and/or explosive eruptions.

Lava flow hazard at Nyiragongo volcano, D.R.C. 1. Model calibration and hazard mapping

The 2002 eruption of Nyiragongo volcano constitutes the most outstanding case ever of lava flow in a big town. It also represents one of the very rare cases of direct casualties from lava flows, which had high velocities of up to tens of kilometer per hour. As in the 1977 eruption, which is the only other eccentric eruption of the volcano in more than 100 years, lava flows were emitted from several vents along a N–S system of fractures extending for more than 10 km, from which they propagated mostly towards Lake Kivu and Goma, a town of about 500,000 inhabitants. We assessed the lava flow hazard on the entire volcano and in the towns of Goma (D.R.C.) and Gisenyi (Rwanda) through numerical simulations of probable lava flow paths. Lava flow paths are computed based on the steepest descent principle, modified by stochastically perturbing the topography to take into account the capability of lava flows to override topographic obstacles, fill topographic depressions, and spread over the topography. Code calibration and the definition of the expected lava flow length and vent opening probability distributions were done based on the 1977 and 2002 eruptions. The final lava flow hazard map shows that the eastern sector of Goma devastated in 2002 represents the area of highest hazard on the flanks of the volcano. The second highest hazard sector in Goma is the area of propagation of the western lava flow in 2002. The town of Gisenyi is subject to moderate to high hazard due to its proximity to the alignment of fractures active in 1977 and 2002. In a companion paper (Chirico et al., Bull Volcanol, in this issue, 2008) we use numerical simulations to investigate the possibility of reducing lava flow hazard through the construction of protective barriers, and formulate a proposal for the future development of the town of Goma.

A new approach to risk assessment of lava flow at Mount Etna

Destruction of human property by lava flow invasion is a significant volcanic hazard at Mount Etna (Italy), where reliable risk maps are important for risk mitigation. We present new high-resolution quantitative risk maps of Mount Etna that are based on lava flow simulations starting from more than 70,000 different potential vents, a probability distribution of vent location, an empirical relationship for the maximum length of lava flows, and a database of buildings. In addition to standard risk maps, which classify areas according to the expected damage at each point, we classify each point of the volcano with respect to the damage that would occur if a vent opened at that point. The resulting maps should help local authorities in making the necessary decisions to deal with ongoing eruptions and to plan long-term land use.

Did the September 2010 (Darfield) earthquake trigger the February 2011 (Christchurch) event

We have investigated the possible cause-and-effect relationship due to stress transfer between two earthquakes that occurred near Christchurch, New Zealand, in September 2010 and in February 2011. The Mw 7.1 Darfield (Canterbury) event took place along a previously unrecognized fault. The Mw 6.3 Christchurch earthquake, generated by a thrust fault, occurred approximately five months later, 6u2005km south-east of Christchurchs city center. We have first measured the surface displacement field to retrieve the geometries of the two seismic sources and the slip distribution. In order to assess whether the first earthquake increased the likelihood of occurrence of a second earthquake, we compute the Coulomb Failure Function (CFF). We find that the maximum CFF increase over the second fault plane is reached exactly around the hypocenter of the second earthquake. In this respect, we may conclude that the Darfield earthquake contributed to promote the rupture of the Christchurch fault.

Heterogeneous large total CO2 abundance in the shallow magmatic system of Kilauea volcano, Hawaii

[1] Due to its very low solubility in silicate melts, CO 2 concentrations in melt inclusions (MIs) within crystals are commonly orders of magnitude less than the total concentration in the multiphase magma, strongly limiting the possibility to constrain CO 2 abundance based on the dissolved quantities. Here we develop a statistical method to process MI data, which allows analytical uncertainties to be taken into account together with the peculiar features of the local saturation surface. The method developed leads to retrieve total H 2 O and CO 2 concentrations in magma as well as the gas phase abundance at the time of magma crystallization. Application to a set of 29 high-resolution secondary ion mass spectrometry (SIMS) MI data from a single specimen of the 1842-1844 eruption of Kilauea, Hawaii, reveals the existence of heterogeneous total CO 2 abundance, and of at least 2-6 wt % total CO 2 in some magma batches, two orders of magnitude higher than the dissolved amounts and 30-50 times more abundant than the corresponding total H 2 O content. Heterogeneous total volatile concentrations are interpreted as due to a combination of degassing and gas flushing in magma subject to convective motion at shallow depth where P 1 wt % is likely to characterize the >30 km deep magma, not represented in the analyzed inclusions, from which a CO 2 -rich gas phase exsolves and decouples from the liquid.

On the occurrence of large earthquakes: New insights from a model based on interacting faults embedded in a realistic tectonic setting

[1]xa0Earthquake occurrence stems from a complex interaction of processes that are still partially unknown. This lack of knowledge is revealed by the different statistical distributions that have been so far proposed and by the different beliefs about the role of some key components as the tectonic setting, fault recurrence, seismic clusters, and fault interaction. Here, we explore these issues through a numerical model based on a realistic interacting fault system. We use an active fault system in central Italy responsible for moderate to large earthquakes, where geometric and kinematic parameters of each structure can be confidently assessed. Then, we generate synthetic catalogs by modeling different seismogenic processes and allowing coseismic and postseismic fault interaction. The comparison of synthetic and real seismic catalogs highlights many interesting features: (1) synthetic seismic catalogs reproduce the short-term clustering and the long-term modulation observed in the historical catalog of the last centuries; (2) a recurrent model of earthquake occurrence on faults is more effective than a Poisson model to explain such short-term and long-term time features; (3) a realistic fault pattern is a key component to generate stochasticity in the seismic catalog, preventing a systematic time “synchronization” of strongly coupled faults; (4) such a stochasticity may put strong limits to the forecasting capability of models based on fault interaction, even though the latter is a key component of the process. Finally, the model allows explicit predictions on future paleoseismological observations to be made.