Seismicity and seismogenic structures in Central Italy: new insigths from the SLAM passive experiment

We investigate the background seismicity of Central Italy in the area including southern Latium, Abruzzi and Molise (SLAM project). Within this region, the central Apenninic chain has been historically affected by many strong earthquakes, some of them very destructive such as the 1349 event (Mw ˜6.7) located at the border between southern Latium and western Molise, the 1654 event (Mw ˜6.4) in the southern Latium-Abruzzi area, and the 1805 Boiano earthquake in the northern Matese range (Mw 6.7). The last important seismic sequence occurred in May 1984 in the Comino Valley, southestern Latium (Mw 5.8). The recent activity is characterized by diffuse low-magnitude seismicity, punctuated by localised small sequences during 2009-2012. Our study focuses on the analysis of seismicity recorded in the period 2009-2013. We present earthquake locations and focal mechanism solutions obtained by standard procedures and an optimized regional 1D velocity model based on the Velest algorithm. The waveform data set was collected from the digital recordings of the permanent stations of the Italian national seismic network, the Abruzzi and Molise regional seismic networks, and from a dense seismic survey carried out in the region between November 2011 and May 2013. The temporary network consisted of 17 three-component seismic stations all equipped with Reftek RT130 digitizers and Lennartz 3D/5s sensors. The deployment of this array improved significantly the detection and location of background seismicity. We relocated more than 4300 events with magnitude ML ranging from about 0.5 to 4.2. Earthquakes distribution shows hypocentral depths concentrated within the upper crust, between 2 and 20 km of depth, and is mostly clustered along the Apenninic chain axis. The computed fault-plane solutions generally display normal fault mechanisms, confirming the extensional NE-SW processes active since Pleistocene in the study region

Seismicity and seismogenic structures in Central Italy: new insigths from the SLAM passive experiment

We investigate the background seismicity of Central Italy in the area including southern Latium, Abruzzi and Molise (SLAM project). Within this region, the central Apenninic chain has been historically affected by many strong earthquakes, some of them very destructive such as the 1349 event (Mw ˜6.7) located at the border between southern Latium and western Molise, the 1654 event (Mw ˜6.4) in the southern Latium-Abruzzi area, and the 1805 Boiano earthquake in the northern Matese range (Mw 6.7). The last important seismic sequence occurred in May 1984 in the Comino Valley, southestern Latium (Mw 5.8). The recent activity is characterized by diffuse low-magnitude seismicity, punctuated by localised small sequences during 2009-2012. Our study focuses on the analysis of seismicity recorded in the period 2009-2013. We present earthquake locations and focal mechanism solutions obtained by standard procedures and an optimized regional 1D velocity model based on the Velest algorithm. The waveform data set was collected from the digital recordings of the permanent stations of the Italian national seismic network, the Abruzzi and Molise regional seismic networks, and from a dense seismic survey carried out in the region between November 2011 and May 2013. The temporary network consisted of 17 three-component seismic stations all equipped with Reftek RT130 digitizers and Lennartz 3D/5s sensors. The deployment of this array improved significantly the detection and location of background seismicity. We relocated more than 4300 events with magnitude ML ranging from about 0.5 to 4.2. Earthquakes distribution shows hypocentral depths concentrated within the upper crust, between 2 and 20 km of depth, and is mostly clustered along the Apenninic chain axis. The computed fault-plane solutions generally display normal fault mechanisms, confirming the extensional NE-SW processes active since Pleistocene in the study region.PublishedGoteborg - Svezia - Joint Assembly IAHS - IAPSO - IASPEI2T. Tettonica attivaope

Preliminary results from seismic monitoring at Nyiragongo Volcano (Democratic Republic of Congo) through telemetered seismic network, Goma volcanological observatory

Following the January 17, 2002 catastrophic eruption of the Nyiragongo Volcano (Democratic Republic of Congo) located in the western branch of the East African Rift, a great effort has been devoted to the seismic surveillance of this volcanic area. The 2002 eruption destroyed one/tenth of the city of Goma, leaving more than 100,000 homeless. In order to correctly monitor the seismic activity at Nyiragongo volcano for both scientific and civil defence purposes, the Istituto Nazionale di Geofisica e Vulcanologia in cooperation with GVO (Goma Volcanological Observatory), between November 2003 and May 2004 installed a new telemetered seismic network consisting of seven digital stations. The network is operational and seismic signals are continuously recorded at the GVO. In this study, we focus mainly on two aspects: (1) the deployment, in the field, of this new digital seismic network and the related real-time data acquisition system, and (2) the first results from a preliminary data analysis based on 6-month seismic recordings. Based on the waveforms and spectral analysis, long-period and very long period events (both, tectonic and volcanic-tectonic earthquakes), have been detected. Furthermore, we succeeded in locating more than 100 earthquakes. These results should strongly encourage the use of such a network data for seismotectonic studies of the area. © 2009 - OGS

Conditions for long-lasting gas eruptions: The 2013 event at Fiumicino International Airport (Rome, Italy)

A hazardous gas eruption from two very close shallow boreholes occurred near the Fiumicino International Airport of Roma (Italy) from August to December 2013. The erupted gas was mostly CO 2 of deep origin and gas output was high and sustained over time reaching values of nearly 20 t day•1. After 3 months, the gas flux was still above 5 t day•1 and was only stopped in December 2013 by long and expensive works of closure of the boreholes. The gas eruption was uncommon as being associated with the building of two mud volcanoes. This style of sustained deep CO 2 eruptions contrasts with the more common short-lived eruptions of shallow biogenic methane-dominated gas pockets. In this work, we present the chronology of the event, the results of geological, geochemical, and geophysical monitoring and a numerical modeling. We propose that the August-December 2013 sustained and prolonged event does not relate to the simple degassing of a shallow, isolated pocket of gas. On the contrary, it reflects very specific conditions in a shallow reservoir (hosted in a 10 m thick gravel layer at –40 m within the Tiber river delta deposits), related to the interplay between the total pressure and the fraction of free CO 2 initially present, across very narrow value ranges around 0.59 MPa and 0.18, respectively. The coexistence of short-lived and long-lived eruptions from the same reservoir suggest that these conditions are not achieved everywhere in the gas reservoir, despite its homogeneous properties. This consideration implies either a pressure compartmentalization of the reservoir, or the occurrence of a transient, possibly associated with an impulsive release of gas from greater depths. The involvement of deeper and larger gas reservoirs connected along faults is evidenced by geophysical investigations. This conceptual model bears significant implications for gas hazard studie