The Italian National Seismic Network and the earthquake and tsunami monitoring and surveillance systems
Alberto MicheliniLucia MargheritiM. CattaneoGianpaolo CecereGiuseppe D’AnnaA. DelladioM. MorettiStefano PintoreAlessandro AmatoA. BasiliAndrea BonoPaolo CasalePeter DanecekM. DemartinLicia FaenzaValentino LaucianiAlfonso Giovanni MandielloAlessandro MarchettiCarlo MarcocciS. MazzaF. MeleAnna NardiC. NostroM. PignoneMatteo QuintilianiSandro RaoLaura ScognamiglioG. Selvaggi
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Abstract. The Istituto Nazionale di Geofisica e Vulcanologia (INGV) is an Italian research institution, with focus on Earth Sciences. INGV runs the Italian National Seismic Network (Rete Sismica Nazionale, RSN) and other networks at national scale for monitoring earthquakes and tsunami as a part of the National Civil Protection System coordinated by the Italian Department of Civil Protection (Dipartimento di Protezione Civile, DPC). RSN is composed of about 400 stations, mainly broadband, installed in the Country and in the surrounding regions; about 110 stations feature also co-located strong motion instruments, and about 180 have GPS receivers and belong to the National GPS network (Rete Integrata Nazionale GPS, RING). The data acquisition system was designed to accomplish, in near-real-time, automatic earthquake detection, hypocenter and magnitude determination, moment tensors, shake maps and other products of interest for DPC. Database archiving of all parametric results are closely linked to the existing procedures of the INGV seismic monitoring environment and surveillance procedures. INGV is one of the primary nodes of ORFEUS (Observatories & Research Facilities for European Seismology) EIDA (European Integrated Data Archive) for the archiving and distribution of continuous, quality checked seismic data. The strong motion network data are archived and distributed both in EIDA and in event based archives; GPS data, from the RING network are also archived, analyzed and distributed at INGV. Overall, the Italian earthquake surveillance service provides, in quasi real-time, hypocenter parameters to the DPC. These are then revised routinely by the analysts of the Italian Seismic Bulletin (Bollettino Sismico Italiano, BSI). The results are published on the web, these are available to both the scientific community and the general public. The INGV surveillance includes a pre-operational tsunami alert service since INGV is one of the Tsunami Service providers of the North-eastern Atlantic and Mediterranean Tsunami warning System (NEAMTWS).Keywords:
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Abstract The Guerrero, Mexico, accelerograph network has recorded, at short distances, earthquakes with magnitudes from 3.0 to 8.1. In this article, the initial 3.5 sec of the P waves, on the vertical component, are compared. In addition to unfiltered accelerograms, several causal bandpass filters are applied. We do not see significant differences, in either original or filtered records, between the initial (e.g., 0.5 sec) seismograms of moderate and large earthquakes. In the original and 2- to 5-Hz passband, the main differences among events with magnitudes over about 4.5 is in the duration of shaking. The initial ground motions of all the large events have very small amplitudes, which gradually get larger. At lower frequencies, seismograms of the largest events show a complex series of multiple pulses, assumed related to failure of numerous asperities. In our lowest frequency band (0.2 to 0.5 Hz), most of the large events that we examined begin with rupture of asperities that are not necessarily larger, and are sometimes smaller, than the asperities that fail during smaller events. The observations are consistent with a model of faulting in which the largest asperities are located at random on the eventual fault plane, and fail when the rupture front, propagating from the hypocenter, reaches them. This allows the largest asperities to occasionally be at the hypocenter and to fail immediately, but for a large fault, it is more likely that they will be located elsewhere and fail later.
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Rapid estimation of the rupture extent of large earthquakes is critical for tsunami warning and emergency response. The hypocenter of a distant earthquake is determined from the first seismic P waves within about 15 minutes after the event. However, methods for determining the size and rupture extent of very large earthquakes rely on long period recordings and aftershock locations, which are not available until several hours or more after the event. Here we introduce a method for rapid estimation of the rupture termination location for large earthquakes based on short period, P ‐wave recordings, available about 30 minutes after an event. The hypocenter and the rupture termination location provide estimates of the extent of rupture and the event size. Application to the 2004, M9 Sumatra‐Andaman earthquake gives a rupture termination location near the Andaman Islands, about 1100 km north of the hypocenter, and a rupture duration of about 8 minutes.
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On April 20, 2013 at 8:02 am, a magnitude 7.0 earthquake occurred in Lushan County, Sichuan Province, China, which induces massive landslides, causes great losses to life and property. Based on the locations of aftershocks provided by the China Earthquake Network Center and the characteristic of Longmenshan active faults system, combined with the current preliminary focal mechanism solution, the fault rupture direction is determined. With the finite fault inversion method, we invert the rupture process of the Lushan M s 7.0 earthquake by teleseismic waveforms data. The inversion results indicate that the main shock is dominated by thrust fault component and the rupture initiated at depth of 15 km, and most of slip ruptured around the hypocenter with the peak slip of about 1.5 m. Most of rupture slips released at the first 20 s and the main rupture occurred at the first 10 s after the onsets of the mainshock. Most of seismic energy released near the hypocenter with a length of 28 km, especially on both sides of the hypocenter with the range of 20 km, and the seismic energy released relatively smaller in other areas. There is a large area with weak slip between the main rupture and another two asperities on both sides of the hypocenter; it may imply that the accumulated strain on the rupture fault has not been completely released. Therefore, there is a significant possibility of having strong aftershocks in the areas where energy is not fully released. This is also the main reason why there are a lot of moderate to strong aftershocks in the Lushan aftershock sequence. In addition, there is an earthquake vacant zone with a length of about 50 km between the Wenchuan M w 7.9 earthquake and this event, which is of high earthquake risk and is deserved to be paid close attention to.
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Abstract Although seismicity near Koyna Reservoir (India) has persisted for ~50 years and includes the largest induced earthquake ( M 6.3) reported worldwide, the seismotectonic framework of the area is not well understood. We recorded ~1800 earthquakes from 6 January 2010 to 28 May 2010 and located a subset of 343 of the highest‐quality earthquakes using the tomoDD code of Zhang and Thurber (2003) to better understand the framework. We also inverted first arrivals for 3‐D Vp , Vs , and Vp / Vs and Poisson's ratio tomography models of the upper 12 km of the crust. Epicenters for the recorded earthquakes are located south of the Koyna River, including a high‐density cluster that coincides with a shallow depth (<1.5 km) zone of relatively high Vp and low Vs (also high Vp / Vs and Poisson's ratios) near Warna Reservoir. This anomalous zone, which extends near vertically to at least 8 km depth and laterally northward at least 15 km, is likely a water‐saturated zone of faults under high pore pressures. Because many of the earthquakes occur on the periphery of the fault zone, rather than near its center, the observed seismicity‐velocity correlations are consistent with the concept that many of the earthquakes nucleate in fractures adjacent to the main fault zone due to high pore pressure. We interpret our velocity images as showing a series of northwest trending faults locally near the central part of Warna Reservoir and a major northward trending fault zone north of Warna Reservoir.
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We have done seismic tomography in and around the focal area of the 2008 Iwate-Miyagi Nairiku Earthquake (M 7.2) occurred on June 14, 2008 in NE Japan. We used data from temporary aftershock observation network deployed just after the occurrence of the present earthquake. Based on the distribution of aftershocks, the fault plane of the mainshock is inferred to dip to the west. Small immediate foreshocks and preceding seismic activity in 1999–2000 on the fault plane in the vicinity of the hypocenter of the mainshock of this earthquake were observed. Lower-seismic-velocity hanging wall can be imaged in the central and the northern part of the focal area. This possibly suggests the present earthquake is a compressional inversion earthquake. The low-velocity zone in the lower crust extends upward to the upper crust, branches into three portions and reaches each active volcano. This low-velocity region can be seen just beneath the mainshock hypocenter and the whole focal area, suggesting that crustal fluid possibly promote the occurrence of the 2008 earthquake.
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