1,721,230 research outputs found
Statistical analysis of Horizontal to Vertical Spectral Ratios (HVSR)
No full textStatistical properties of the horizontal to vertical spectral ratios (HVSR) applied to noise recording are analyzed in order to define optimal strategies for numerical processing and identification of possible artifacts. To this purpose, two time series have been analyzed: one constituted by environmental seismic noise in the presence of a genuine physical signal and one relative to pure instrumental noise, both obtained with the same experimental apparatus. By means of suitable statistics, some guidelines for the HVSR analysis are provided. A statistical test proposed by Albarello (2001) for the identification of artifacts in the HVSR function has been analyzed and invalidated
Applying the damage assessment for rapid response approach to the august 24 M6 event of the seismic sequence in central Italy (2016)
Full text linkSeismic monitoring networks are increasingly being used in urban areas to record and locate earthquakes. Recordings in the proximity of buildings also allow assessing, as a first approximation, the expected building damage. The DARR (Damage Assessment for Rapid Response) method provides local-scale information on expected damage patterns. The potential of this approach is discussed here for the August 24 M6 event of the Central Italy seismic sequence (2016-2017). We focus only on the first event of the sequence because cumulative damage is outside the scope of this study. The earthquake recordings are available from two Italian monitoring networks: the Italian Accelerometric Archive (ITACA) and the OSS (Osservatorio Sismico delle Strutture), which collects data from monitored buildings and bridges in Italy. We selected four target areas (Amatrice, Norcia, Visso and Sulmona) characterized by different epicentral distances and building typologies, that suffered different levels of damage during the M6 event on 24 August 2016. Using recordings either in the free field or in the basement of buildings, the expected relative displacement of building typologies common in the studied areas is calculated with the DARR method. Using predefined damage thresholds from literature, the obtained results allow quantifying the expected damage for dominant building typologies in the surroundings of the recording sites. We investigate and discuss the potential use and applicability of the DARR method in different areas depending on the epicentral distance and building characteristics. The results indicate that the DARR approach is useful for supporting and improving rapid response activities after a seismic event
The Damage Assessment for Rapid Response (DARR) Method and its Application to Different Ground-Motion Levels and Building Types
Full text linkSeismic recordings in buildings and on the ground are increasingly available due to the increment and expansion of seismic monitoring networks worldwide. However, most urban strong‐motion networks consist of stations installed at the ground or, less frequently, in selected building’s basement. It is, therefore, of utmost importance to develop methods that can provide estimates of expected structural damage, starting from earthquake recordings at the ground level. Damage Assessment for Rapid Response (DARR) provides first‐level estimates of the expected damage to buildings, based on ground‐motion recordings and simple information on buildings’ characteristics. In this work, we apply DARR using both weak and strong ground‐motion recordings available for different low‐ and mid‐rise building typologies. A total of 9 buildings and 19 earthquake recordings were analyzed. DARR reproduces the shaking at the building’s top, and estimates the peak structural relative displacement or average interstory drift. Results show that the method works well for the considered building types and ground‐motion levels for the estimation of relative and total displacements using first‐order assessments. Comparison with the previously defined thresholds allows the estimation of expected damage. Our results (i.e., no damage for most buildings and events) are consistent with the absence of damaging events in northeastern Italy in the studied period (2019–2021). For a school building in central Italy, which was heavily damaged by the 2016 Central Italian sequence, DARR correctly predicted this fact
Performance of the GFZ Decentralized On-Site Earthquake Early Warning Software (GFZ-Sentry): Application to K-NET and KiK-Net Recordings, Japan
No full textEstimating Cross-Coupling in Site Response by Seismic Noise Interferometry: An Example from an Alpine Valley (Northeastern Italy)
No full textThe assessment of site response is an important task for improved seismic hazard estimation. The standard tools and approaches, however, generally neglect the cross-coupling effect among the three components of motion due to heterogeneities in the underground structure. In this study, we propose a means to estimate cross-coupling effects by the inversion of the deconvolved wavefield derived from seismic noise analysis. These functions are obtained by deconvolving the three components of the ground motion recorded at a site with those recorded at a reference site. The proposed procedure is applied to a set of recordings collected in the Sarca Valley (northeastern Italy) by a temporary seismometric network. The results show that the cross-coupling components are not negligible, and are related to lateral variations in the bedrock surface and heterogeneities within the sedimentary cover
On-site structure-specific real-time risk assessment: perspectives from the REAKT project
No full textAnomalously deep earthquakes in northwestern Italy
No full textIt is usually assumed that earthquakes in intraplate regions occur in the upper crust, and northwestern Italy is generally assigned to this kind of 'normal' seismicity. In this work, the depth distribution of the events localized in this area by the Istituto Geofisico Geodetico (IGG) seismic network in the period 1991-1997 is analyzed in detail. In particular, the location capability of the network is discussed, adopting as reference quarry blasts (for the epicentral position) and the locations obtained from a dense temporary network (for the depth estimate). Within the so-obtained error limits, the depth distribution of events show a characteristic pattern: while for most of the area covered by the network the well-located seismicity lies within the first 20 km of depth, in a band following the inner arc of the Western Alps, numerous events have anomalously large focal depths, reaching a maximum of 114 km. These depth determinations cannot be attributed to instabilities of the location procedure: different choices of the propagation models used for the hypocentral determination led to very similar depth values, always significantly larger than the standard values for the surrounding areas. A strong correlation has been found between the 3-dimensional distribution of these foci and the P-wave propagation anomalies obtained from tomographic studies, suggesting a direct link between elastic and rheological properties of lower crust and upper mantle in this area
The 9 October 1963 Vajont Catastrophe from the Point of View of the WWSSN-LP Recordings of the TRI-117 Station, Trieste, Italy
Full text linkIn this study, we analyze the seismic signal generated by the 1963 Vajont catastrophic landslide recorded at the Worldwide Standardized Seismographic Station Network- Long Period station of Trieste (Italy). The landslide (nearly 260–270 million m3) invaded an artificial reservoir designed for electrical production, and generated a 220 m high wave that flowed over the dam and claimed the lives of approximately 2000 people. The original seismograms have been digitized and analyzed using time–frequency tools and numerical simulations. The results indicate that a seismic signal comparable to that generated by an Ms 3.7 earthquake was generated by the landslide. Furthermore, the calculatednearly2×1014 Joffrictionalenergy,consideringtheknownparameterofthe mass movement, is compatible with a friction coefficient of 0.29, in excellent agreement with the values from previous studies. The seismic efficiency that we calculate (1:12 × 10−4 –4:45 × 10−4 ), also taking into account available data on the landslide, is within the range of values previously noted in literature. Finally, via the numerical sim- ulations and adopting an ad hoc crustal model for the area, the origin time of the event is estimated at 21 hr 41 min 42 s UTC. The results confirm the importance of the re-analy- sis of analog seismograms with modern tools within a multihazard context
New relationships between V-s, thickness of sediments, and resonance frequency calculated by the H/V ratio of seismic noise for the Cologne area (Germany)
No full textNoise measurements were carried out in the Cologne area. (Germany), and the resonance frequency of each site was estimated from the main peak in the spectral ratio between the horizontal and vertical component. For 32 of these sites, the thickness of the sedimentary cover was known from boreholes, and a clear correlation between resonance frequency and sediment thickness was observed. A formula that correlates cover thickness with frequency of the main peak in the horizontal-to-vertical spectral ratio was derived. In addition, a best-fitting shear-wave-velocity distribution with depth, v(s)(z), as well as a relationship between average shear-wave velocity (V) over bars and thickness of the sedimentary cover, was calculated. By using all of the noise measurements and applying the derived relationships, we obtained a subsoil classification for the Cologne area
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