Epicentral Distance Research Articles

Monitoreo de la salud estructural de un edificio residencial de muros de corte de hormigón armado en Lima, Perú, utilizando un sensor 4d raspberry shake

Lima, the capital of Peru, has not suffered from a great earthquake since 1746, making this a prone Mw 8.8 earthquake area according to seismological studies. In this context, seismic structural health monitoring presents an opportunity to assess rapidly buildings after a great earthquake and protect inhabitant from those buildings with high risk of collapse due to aftershocks. A basic seismic structural health monitoring arrangement of a fifteenth-floor residential building is presented using a low-cost sensor called Raspberry Shake 4D. The implemented sensor incorporates both a vertical velocity geophone and three orthogonally positioned microelectromechanical systems accelerometers. The building is a reinforced concrete shear walls structure located in Comas, north of Lima. More than thirty seismic events have been recorded, including the Mw 8.0 Lagunas earthquake (05/26/2019) and the Mw 5.8 (22/06/2021) with epicentral distances of 709 km and 94 km, respectively. Acceleration as high as 150 cm/s2 and as low as 2 cm/s2 have been recorded. It was possible to obtain fundamental frequencies of vibration in longitudinal and transversal directions of the building from the response calculated using the wavelet transform that have a good agreement with results of microtremor measurements performed at different floors. The computed scalograms for seismic records showed important values of energy amplitudes for the fundamental frequencies of the building. Finally, theoretical fundamental frequencies were obtained from a 3D finite element model and an elastic analysis.

Seismic Damage Scenarios Induced by Site Effects on Masonry Clustered Buildings: A Case Study in South Italy

ABSTRACT The present research aims to explore the influence of site effects on the seismic vulnerability of the historical centre of Baranello, a little town in the Molise Region of Italy. Structural and typological classification of the investigated urban area has been done according to the EMS-98 scale. The vulnerability assessment of the inspected historical buildings has been carried out through an appropriate survey form to identify the buildings most susceptible to seismic damage. Consequently, using the Post-Earthquake Damage and Safety Assessment (AeDES) form implemented by the Italian Civil Protection Department (DPC), the typological vulnerability curves of the built-up area have been derived based on the damages recorded after the 2002 Molise earthquake. Finally, a local amplification factor, which increases the severity of the seismic damage to the structures, has been taken into account based on the time-domain method. Results reveal that the local amplification effects significantly increase the expected damage, which should lead to the collapse of almost all the investigated buildings for epicentre distance of 5.0 km and magnitude of 6.0. This means that the proposed simplified approach can represent a useful tool to more appropriately foresee the seismic risk of urban centres.

Strong Ground Motion Recorded by High-Rate GPS during the 2021 Ms 6.4 Yangbi, China, Earthquake

Abstract The 2021 Ms 6.4 Yangbi earthquake, Yunnan, China, was recorded by the Dali Global Positioning System (GPS) network comprising 37 permanent stations within 100 km of the epicenter. All of these GPS stations recorded 1 Hz data, and 12 of them also recorded 5 Hz data. Using sophisticated data processing strategies, especially the method to overcome ionospheric and multipath errors, near-field waveforms of epoch-by-epoch displacement of all of the GPS stations within an epicentral distance of ∼50 km were derived from high-rate GPS observations with a root mean square error of 3.8, 4.2, and 8.2 mm for the east–west, north–south, and up components, respectively. The peak ground displacement of up to 14 cm in the horizontal direction and 4.2 cm in the vertical direction and the largest coseismic displacement of 3.1 cm in the horizontal direction and 3.2 cm in the vertical direction were observed for the stations within 6–9 km of the epicenter. The waveforms, with dominant periods between 7 and 10 s, present a systematic change in shape as a function of distance from the source, which demonstrates that the high-rate GPS observations can provide reliable relative-displacement response spectra at the periods needed in the design of large structures for resisting strong earthquakes. Comparisons of the GPS displacement time series at 1, 2.5, and 5 Hz suggest that 5 Hz data are able to capture strong ground information that are of interest to both earthquake seismologists and engineers. We conclude that the displacement waveforms and motion trajectories from high-rate GPS observations provide unique additional information of the near-field strong ground motion that is valuable to seismologists in unraveling the dynamic process of fault rupture and to engineers for designing large structures with very long period response.

Crustal anisotropy beneath southeastern Tibet inferred from directional dependence of receiver functions

The present study reveals depth-dependent crustal anisotropic signatures beneath southeastern Tibet. It is used to characterize the rheology of major faults and shear zones, which is important for understanding crustal deformation and geodynamic processes beneath the study area. The depth-dependent anisotropic orientations have been investigated based on the directional dependence of radial and tangential receiver functions (RFs). To achieve our objective, we first computed 3683 good-quality P-RFs from 174 teleseismic earthquakes (M ≥ 5.5) recorded within epicentral distance range of 30∘ to 90∘ at 70 seismic stations of the Eastern Syntaxis experiment (XE Network). After that, we employed the harmonic decomposition technique at each seismic station to retrieve the first (k = 0), second (k = 1) and third (k = 2) degree harmonics from the RF dataset. Our study characterizes the type (horizontal or plunging) of the symmetry axis. The anisotropic axes of the upper crust (0–20 km) appear to vary from approximately N-S to NE-SW. They are usually orthogonal to orientations of major faults and suture zones in the region, implying the effect of structure-induced anisotropy. It can be explained by regularly oriented cracks or macroscopic structure alignment along the major faults. The anisotropic orientations of the middle crust (20–40 km) are NE-SW to E-W direction, reflecting a different pattern than those estimated in the upper crust. The lower crustal (40–70 km) anisotropic pattern (E-W or ESE-WNW direction) exhibits distinct orientations than the upper and middle crust. The crystal preferred orientations (CPO) of the mica and amphibole minerals are likely to cause anisotropy observed at mid-to-lower crustal depth ranges, emphasizing the role of ductile deformation due to material movement towards the east underneath southeastern Tibet. Our results, along with S(K)KS and direct S-waves splitting signatures, suggest mid-to-lower crust and lithospheric mantle material movement towards the east, while the discrepancies in anisotropic symmetric axes directions may be indicative for the partial coupling between the crust and upper mantle beneath the region.

APPLICATION OF AHP TO RISK ASSESSMENT OF ASEISMIC CAPACITY OF BUILDINGS

This study is proposed to apply the analytical hierarchy process (AHP) for risk assessment of aseismic capacity of buildings. A framework of hierarchical structure of risk assessment of a building is proposed, in which target level, major level and sub level are included. In the major level, 4 important influence factors are considered, i.e., earthquake features (EF), geological conditions (GC), structural characteristics (SC), and structural design (SD). In the sub-layer totally 15 influence factors are depicted: epicenter distance (ED), source depth (SD), earthquake magnitude (EM), tsunami potential (TP), soil property (SP), slope angle (SA), liquefaction potential (LP), fault zone (FZ), cracks and defects (CD), crack position (CP), shear resistance (SR), twisting resistance (TR), aseismic apparatus (AA), construction type (CT), and form factors (FF). After pairwise comparison matrices of each layer are constructed and analyzed by AHP, we can obtain the relative risk impact (RRI) for 15 influence factors. Then we establish assessment criteria. Finally, we apply this process to check the validity of AHP for risk assessment of 7 practical cases of buildings during earthquakes based on the overall risk index (ORI), among these cases 4 buildings were destroyed and 3 were safe. The results show that AHP is an efficient, convenient and rapid approach for quantitative risk aseismic capacity of existing buildings subjected to earthquakes.

Quantification of Small-Scale Heterogeneity at the Core–Mantle Boundary Using Sample Entropy of SKS and SPdKS Synthetic Waveforms

Qualitative and quantitative analysis of seismic waveforms sensitive to the core–mantle boundary (CMB) region reveal the presence of ultralow-velocity zones (ULVZs) that have a strong decrease in compressional (P) and shear (S) wave velocity, and an increase in density within thin structures. However, understanding their physical origin and relation to the other large-scale structures in the lowermost mantle are limited due to an incomplete mapping of ULVZs at the CMB. The SKS and SPdKS seismic waveforms is routinely used to infer ULVZ presence, but has thus far only been used in a limited epicentral distance range. As the SKS/SPdKS wavefield interacts with a ULVZ it generates additional seismic arrivals, thus increasing the complexity of the recorded wavefield. Here, we explore utilization of the multi-scale sample entropy method to search for ULVZ structures. We investigate the feasibility of this approach through analysis of synthetic seismograms computed for PREM, 1-, 2.5-, and 3-D ULVZs as well as heterogeneous structures with a strong increase in velocity in the lowermost mantle in 1- and 2.5-D. We find that the sample entropy technique may be useful across a wide range of epicentral distances from 100° to 130°. Such an analysis, when applied to real waveforms, could provide coverage of roughly 85% by surface area of the CMB.

MAGNITUDE SENSITIVITY OF KARATAYU SEISMIC ARRAY IN MONITORING OF SEISMICITY IN CENTRAL ASIA

The capability to record events of different magnitude at various epicentral distances (magnitude sensitivity of the station) was studied basing on representative statistical material ontained by the results of Karatayu seismic array operation for more than 10 years period. The dependence of magnitude sensitivity on azimuth of seismic waves arrival was studied. It is shown that depending on the direction, the station has different capabilities in recoding of small earthquakes at the same distance. The examples of small events recorded by Karatayu station are shown by a series of two explosions of shells at military warehouses in the south Kazakhstan in 2019 and 2021.

PAHUTE MESA TRAVEL TIMES AT KURIL–KAMCHATKA SEISMIC STATIONS

This research fulfills additional information about the lithosphere below Southeastern Asia and the northern Pacific. The area is interesting for researchers because of the Kuril–Kamchatka subducted lithosphere. The availability to study an underground structure is complicated, because of Pacific Ocean. The significance of this research concerns epicentral distances ~54°–70° or ~6000–7000 km. During the Cold War of the 20th century and the classification of information between the largest nuclear states the Soviet Union (USSR) and the United States of America (USA), data on the registration of nuclear explosions were not published, however, underground nuclear explosions (UNE) were recorded. Thanks to an employee of the laboratory 5-s of the Institute of Physics of the Earth named after O.Yu. Schmidt of the USSR Academy of Sciences Kh.D. Rubinstein is kept at the Institute for the Dynamics of Geospheres of the Russian Academy of Sciences named after Academician M.A. Sadovsky (IDG RAS). Only after 1985 reports from some seismic stations of the former USSR began to be published in the operational reports of the United Geophysical Survey of the Russian Academy of Sciences (GS RAS). As it has not been yet published anywhere, we collect them and obtain the travel times were by revising seismograms from the archives IDG RAS and GS RAS for five Kuril–Kamchatka seismic stations (Bering, Esso, Severo-Kurilsk, Kurilsk). The 48 Unites States UNE at Pahute Mesa (at Nevada Test Site) from 1968 to 1990 are used for travel time curve building. We measure P waves travel times (tp) on historical seismograms for the ray travel path between Pahute Mesa tests and Kuril–Kamchatka stations. The body-waves magnitudes (mb) vary from 5.3 to 6.5. We obtain arrivals for: 1 UNE at Bering station, 7 UNE at Esso station, 45 UNE at Petropavlovsk, 18 UNE at Severo-Kurilsk and 12 at Kurilsk. We build a travel time function using linear regression algorithm as tp=k·Δ°+b, where Δ° is the epicentral distance, k and b are arbitrary constants. We show that travel time deviations, associated with nonlinearity of the Earth. We estimate the effective velocities of P waves for the Pahute Mesa – Kuril–Kamchatka travel path as coefficient k in the linear equation. Effective velocity is equal to 7.5 km/s.

Inner Core Rotation Captured by Earthquake Doublets and Twin Stations

AbstractThe Earth's solid inner core (IC) is generally believed to rotate relative to the mantle, but the proposal remains controversial. Here we use seven waveform doublets in the South Sandwich Islands region with time lapses of 5.8–17.0 years that are recorded by two close stations in Kyrgyzstan with virtually the same epicentral distance. The fortuitous geometry allows precise measurements of the IC temporal changes and the underlying local structure at the same time. The remarkable observations in waveforms and spatial‐temporal measurements show unequivocally that the IC must have shifted (rotated) eastward in 1991–2010 and help determine accurately the average rotation rate as 0.127 ± 0.006°/yr at 95% confidence level during the time span.

Epicenter localization using forward-transmission laser interferometry.

Widely distributed optical fibers, together with phase-sensitive laser interferometry, can expand seismic detection methods and have great potential for epicenter localization. In this paper, we propose an integral response method based on a forward transmission scheme. It uses spectrum analysis and parameter fitting to localize the epicenter. With the given shape of the fiber ring, the integral phase changes of light propagating in the forward and reverse directions can be used to determine the direction, depth, distance of the epicenter, and seismic wave speed. For the noisy case with SNR = 20 dB, the simulation results show ultrahigh precision when epicenter distance is 200 km: the error of the orientation angle is ∼0.003°±0.002°, the error of the P-wave speed is ∼0.9 ± 1.2 m/s, the error of the epicenter depth is ∼9.5 ± 400 m, and the error of the epicenter distance is ∼200 ± 760 m.

Testing Site Amplification Curves in Hybrid Broadband Ground Motion Simulations of M6.0, 24 August 2016 Amatrice Earthquake, Italy

This research focuses on predicting and assessing earthquake impact due to future scenarios regarding the ground motion seismic hazard by accounting mainly for site effect in the Central Apennines. To this end, we produced synthetic broadband seismograms by adopting a hybrid simulation technique for the Mw6.0 Amatrice earthquake, Central Italy, on 24 August 2016, accounting for site conditions by means of amplification curves, computed with different approaches. Simulations were validated by comparing with data recorded at 57 strong-motion stations, the majority installed in urban areas. This station sample was selected among stations recording the Amatrice earthquake within an epicentral distance of 150 km and potentially prone to experience site amplification effects because of lying in particular site conditions (sedimentary basins, topographic irregularities, and fault zones). The evaluation of amplification curves best suited to describe local effects is of great importance because many towns and villages in central Italy are built in very different geomorphological conditions, from valleys and sedimentary basins to topographies. In order to well reproduce observed ground motions, we accounted for the site amplification effect by testing various generic and empirical amplification curves such as horizontal-to-vertical spectral ratios (calculated from Fourier spectra using both earthquake, HVSR, and ambient noise, HVNSR, recordings) and those derived from the generalized inversion technique (GIT). The site amplifications emanated from GIT improve the match between observed and simulated data, especially in the case of stations installed in sedimentary basins, where the empirical amplification curve effectively reproduces spectral peaks. On the contrary, the worst performances are for the spectral ratios between components, even compared to the generic site amplification, although the latter ignores the strong bedrock/soil seismic impedance contrasts. At sites on topography, we did not observe any systematic behavior, the use of empirical curves ameliorating the fit only in a small percentage of cases. These results may provide a valuable framework for developing ground motion models for earthquake seismic hazard assessment and risk mitigation, especially in urban areas located in the seismically active central Italy region.

Mantle Q structure from S, SS, SSS and SSSS amplitude measurements

SUMMARY The seismic quality factor (Q) of the Earth’s mantle is of great importance for the understanding of the physical and chemical properties that control mantle anelasticity. The radial structure of the Earth’s Q is less well resolved compared to its wave speed structure, and large discrepancies exist among global 1-D Q models. In this study, we build a global data set of amplitude measurements of S, SS, SSS and SSSS waves using earthquakes that occurred between 2009 and 2017 with moment magnitudes ranging from 6.5 to 8.0. Synthetic seismograms for those events are computed in a 1-D reference model PREM, and amplitude ratios between observed and synthetic seismograms are calculated in the frequency domain by spectra division, with measurement windows determined based on visual inspection of seismograms. We simulate wave propagation in a global velocity model S40RTS based on SPECFEM3D and show that the average amplitude ratio as a function of epicentral distance is not sensitive to 3-D focusing and defocusing for the source–receiver configuration of the data set. This data set includes about 5500 S and SS measurements that are not affected by mantle transition zone triplications (multiple ray paths), and those measurements are applied in linear inversions to obtain a preliminary 1-D Q model QMSI. This model reveals a high Q region in the uppermost lower mantle. While model QMSI improves the overall datafit of the entire data set, it does not fully explain SS amplitudes at short epicentral distances or the amplitudes of the SSS and SSSS waves. Using forward modelling, we modify the 1-D model QMSI iteratively to reduce the overall amplitude misfit of the entire data set. The final Q model QMSF requires a stronger and thicker high Q region at depths between 600 and 900 km. This anelastic structure indicates possible viscosity layering in the mid mantle.

Seismic Hazard Analysis Using Fuzzy-Probabilistic Approach for Chennai City, South India

Fuzzy-probabilistic seismic hazard analysis (FPSHA) is performed for Chennai city, South India incorporating both the random and fuzzy uncertainties. Randomness is handled using Monte-Carlo simulation technique, and fuzziness is accounted in the hazard analysis using fuzzy logic. The magnitude of earthquakes and epicentral distances are fuzzified and used as inputs in the fuzzy inference rules. Fuzzy attenuation relationships are developed as consequence of the inference rules with the help of ground-motion models and ANFIS. The proposed FPSHA method has the advantage over the conventional hazard analysis methods in respect of its preciseness, efficiency, practicability, and reliability. The ground motions compatible with the target spectrum (UHS) of 475 years return period are selected from the recorded accelerograms with appropriate scaling. The established spectrum compatible accelerograms are vital in the seismic analysis and design of infrastructure facilities and rehabilitation and strengthening of historical and critical structures.

APPLICATION OF AHP TO RISK ASSESSMENT OF ASEISMIC CAPACITY OF BUILDINGS

This study is proposed to apply the analytical hierarchy process (AHP) for risk assessment of aseismic capacity of buildings. A framework of hierarchical structure of risk assessment of a building is proposed, in which target level, major level and sub level are included. In the major level, 4 important influence factors are considered, i.e., earthquake features (EF), geological conditions (GC), structural characteristics (SC), and structural design (SD). In the sub-layer totally 15 influence factors are depicted: epicenter distance (ED), source depth (SD), earthquake magnitude (EM), tsunami potential (TP), soil property (SP), slope angle (SA), liquefaction potential (LP), fault zone (FZ), cracks and defects (CD), crack position (CP), shear resistance (SR), twisting resistance (TR), aseismic apparatus (AA), construction type (CT), and form factors (FF). After pairwise comparison matrices of each layer are constructed and analyzed by AHP, we can obtain the relative risk impact (RRI) for 15 influence factors. Then we establish assessment criteria. Finally, we apply this process to check the validity of AHP for risk assessment of 7 practical cases of buildings during earthquakes based on the overall risk index (ORI), among these cases 4 buildings were destroyed and 3 were safe. The results show that AHP is an efficient, convenient and rapid approach for quantitative risk aseismic capacity of existing buildings subjected to earthquakes.

Analysis of earthquake hazards prediction with multivariate adaptive regression splines

<p><span>Earthquake research has not yielded promising results, either in the form of causes or revealing the timing of their future events. Many methods have been developed, one of which is related to data mining, such as the use of hybrid neural networks, support vector regressor, fuzzy modeling, clustering, and others. Earthquake research has uncertain parameters and to obtain optimal results an appropriate method is needed. In general, several predictive data mining methods are grouped into two categories, namely parametric and non-parametric. This study uses a non-parametric method with multivariate adaptive regression spline (MARS) and conic multivariate adaptive regression spline (CMARS) as the backward stage of the MARS algorithm. The results of this study after parameter testing and analysis obtained a mathematical model with 16 basis functions (BF) and 12 basis functions contributing to the model and 4 basis functions not contributing to the model. Based on the level of variable contribution, it can be written that the epicenter distance is 100 percent, the magnitude is 31.1 percent, the location temperature is 5.5 percent, and the depth is 3.5 percent. It can be concluded that the results of the prediction analysis of areas in Lombok with the highest earthquake hazard level are Malaka, Genggelang, Pemenang, Tanjung, Tegal Maja, Senggigi, Mangsit. Meninting, and Malimbu.</span></p>

Performance of a Rotational Sensor to Decipher Volcano Seismic Signals on Etna, Italy

AbstractVolcano‐seismic signals such as long‐period events and tremor are important indicators for volcanic activity and unrest. However, their wavefield is complex and characterization and location using traditional seismological instrumentation is often difficult. In 2019 we recorded the full seismic wavefield using a newly developed 3C rotational sensor co‐located with a 3C traditional seismometer on Etna, Italy. We compare the performance of the rotational sensor, the seismometer and the Istituto Nazionale di Geofisica e Vulcanologia‐Osservatorio Etneo (INGV‐OE) seismic network with respect to the analysis of complex volcano‐seismic signals. We create event catalogs for volcano‐tectonic (VT) and long‐period (LP) events combining a STA/LTA algorithm and cross‐correlations. The event detection based on the rotational sensor is as reliable as the seismometer‐based detection. The LP events are dominated by SH‐type waves. Derived SH phase velocities range from 500 to 1,000 m/s for LP events and 300–400 m/s for volcanic tremor. SH‐waves compose the tremor during weak volcanic activity and SH‐ and SV‐waves during sustained strombolian activity. We derive back azimuths using (a) horizontal rotational components and (b) vertical rotation rate and transverse acceleration. The estimated back azimuths are consistent with the INGV‐OE event location for (a) VT events with an epicentral distance larger than 3 km and some closer events, (b) LP events and tremor in the main crater area. Measuring the full wavefield we can reliably analyze the back azimuths, phase velocities and wavefield composition for VT, LP events and tremor in regions that are difficult to access such as volcanoes.

Minimum 1D VP and VP/VS Models and Hypocentral Determinations in the Central Mediterranean Area

Abstract Minimum 1D velocity models and station corrections have been computed for the central Mediterranean area using two main data sets. The first one consists of accurate first arrival-time readings from 103 seismic events with magnitude (ML)≥3.5 recorded by the Italian National Seismic Network (RSN) and the AlpArray Seismic Network (AASN) in the period 2014–2021. Earthquakes were selected on the basis of their spatial distribution, epicentral distance to the nearest seismic station, and maximum distance traveled by Pn and Sn phases. This fine selection of high-quality data combined with the spatial density of the AlpArray seismic stations was decisive in obtaining high resolution for upper mantle velocity, especially in the Alpine belt. To obtain a denser coverage of crustal rays, we extended the first data set with P and S arrivals of local earthquakes from Istituto Nazionale di Geofisica e Vulcanologia (INGV) bulletin data (2016–2018). A total of 75,807 seismic phases (47,183 P phases and 28,264 S phases) have been inverted to calculate best-fit 1D velocity models, at regional and local scales. We then test the performance of the optimized velocity models by relocating the last four years of seismicity recorded by INGV (period 2017–2020). The computed velocity models are very effective for routine earthquake location, seismic monitoring, source parameter modeling, and future 3D seismic tomography.

Correlation between the tilt anomaly on the vertical pendulum at the Songpan station and the 2021 MS7.4 Maduo earthquake in Qinghai province, China

Understanding the relationship between precursory deformation anomalies and strong earthquakes is vital for physical earthquake prediction. Six months before the 2021 MS7.4 Maduo earthquake in Qinghai province, China, the vertical pendulum at the Songpan station was observed to tilt southward with a high rate and large amplitude. Studies conducted before the 2021 MS7.4 Maduo earthquake inferred the tilt anomaly to be an earthquake precursor. However, after the earthquake, the relation between the earthquake and the anomaly became controversial, partly because the Songpan station is located at a great distance from the epicenter. In this study, based on the deformation anomaly characteristics, relationship between the seismogenic fault and the fault near the anomaly, and associated quantitative analyses, we concluded that this anomaly may be associated with the 2021 MS7.4 Maduo earthquake. The duration and amplitude of this anomaly matched with the magnitude and epicenter distance of the Maduo earthquake. We have also interpreted the reason why the anomaly occurred near a fault that is obliquely intersected with the seismogenic fault and why the anomaly is located far from the earthquake epicenter.

Liquefaction assessment of gravelly soils: the role of in situ and laboratory geotechnical tests through the case study of the Sulmona basin (Central Italy)

Even though liquefaction in gravelly soil is well documented in many earthquakes since 1891, most of the “simplified procedures” and national buildings codes still consider only sandy soil liquefaction in seismic hazard assessment. In this study, 109 sites of gravel liquefaction related to 27 historical earthquakes from 1891 to 2020 are reported, with a wide range of moment magnitudes, Mw , (5.3 to 9.2) and focal depths (5.4 to 33 km), highlighting the potential for liquefaction of gravelly soils even during moderate earthquakes. Although gravels are often thought to have hydraulic conductivities high enough to preclude liquefaction, gravels that have liquefied are generally well-graded sandy gravels. The sand content is typically 30% or more so that the hydraulic conductivity is governed by the sand size making them clearly liquefiable. Even for gravels with lower sand contents, a low permeability surface layer has often been observed that could restrict drainage and produce excess pore pressure during strong shaking.The epicentral distance calculated for gravel liquefaction sites plotted vs the magnitude of the earthquake event shows a pattern which closely follows similar curves provided in the literature for sandy soils. However, field observations of liquefaction in gravelly soils are less frequent in the historical record.In addition to examining gravel liquefaction sites in general, this paper provides a case history illustrating the difficulties of liquefaction assessment in gravels at a site in Santa Rufina (Sulmona basin, Central Italy). This site, characterised by high vertical and lateral stratigraphic variability, was selected for gravel liquefaction assessment using a combination of in-situ tests, laboratory geotechnical analysis, and geological studies. We found that, even if SPT- and DPT- based in-situ methods provide conflicting results, the availability of a borehole log, along with standard laboratory test results, proved to be fundamental to achieving a reliable assessment of the liquefaction hazard.

Characterization of Distant and Moderate Earthquakes with Inexpensive MEMS Sensors: Application to the Mw 6.3, 29th December 2020, Petrinja Event.

In this work, we evaluate the suitability of a new MEMS sensor prototype, called ASX1000 (ADEL s.r.l., Modena, Italy), for the monitoring of distant and moderate seismic events. This device is an inexpensive capacitive accelerometer with a relatively low level of instrumental noise; it can record both local and far seismic events. An experimental network built with ASX1000 MEMS, located in northern Italy, was able to record the Mw 6.3 Petrinja earthquake that occurred in December 2020; it had an epicentral distance of more than 350 km. We retrieved the strong motion parameters (PGA, pseudo-absolute velocity, and pseudo-absolute spectral acceleration) from the acceleration time histories recorded by the MEMS sensors. The obtained parameters were compared with the ones obtained by the closer high-quality seismometers, belonging to the INGV National Seismic Network. The comparison to the highest-quality sensors confirms a reasonable agreement of the inferred parameters. This work suggests that—in the near future—MEMS sensors could be adopted to integrate the existing seismic network. A denser coverage of sensors can sample more accurately the seismic wavefield, taking into account the large spatial variability of local geology and the relative differences in seismic response.