Seismic Sequence Research Articles

Rapid Near-Field Attenuation of Ground Motion from Shallow Induced Earthquakes, Case Study: Preston New Road, United Kingdom

Abstract Ground motions from shallow induced earthquakes and tectonic seismicity were investigated in this study by directly modeling the seismic attenuation quality factor (Q) using spectral fitting and coda envelope decay methods. We use data from the Preston New Road (PNR) shale gas induced seismicity sequences near Blackpool, United Kingdom, in 2018 and 2019, in addition to regional tectonic events in the United Kingdom. Our results show that the local Q obtained from the induced seismic sequences at PNR, attributed to shallower layers in the crust, leads to a rapid rate of near-field decay (sudden loss in amplitude of earthquake signal over a short distances), with significantly stronger attenuation than observed for regional events. We furthermore find that estimates of Q are nonunique to a given record, differing both with the method and the analysis windows used, particularly at high frequency. These differences can be attributed to the different modeling methodologies (e.g., different assumptions) or to fundamental differences in physical attenuation processes within the seismic wavefield itself, which traverses multiple ray paths and comprises various phases. Our results indicate that to model ground motions for shallow earthquakes, it is important to consider the composite Q along a specific path rather than an average regional Q. To this extent, a depth-dependent attenuation model is considered crucial to bridge the gap between shallow induced earthquakes and tectonic seismicity.

Magnitude distribution and clustering properties of the 3-D seismicity in Central Apennines (Italy)

SUMMARYIn this paper we deal with statistical features of earthquakes, seeking possible correlations between the Gutenberg–Richter magnitude distribution and the short-term clustering in an area of the Central Apennines, Italy, where significant seismicity with earthquakes exceeding magnitude 6.0 has been repeatedly observed from 1990 to the present. For this purpose, a recently developed version of the ETAS model, incorporating a 3-D spatial triggering kernel, has been adopted. Our analysis has been carried out representing the b-value and the probability of independence of events on six vertical cross-sections suitably related to the seismic structures that are considered responsible of the seismicity observed in the study area. The results of the statistical analysis of the seismicity in the study area have shown a clear distinction between the western normal low-angle fault system, characterized by eastward dip and the eastern normal fault systems, with westward dip. In the former (Etrurian Fault System; EFS) we found seismicity with a high b-value and high probability of independence, that is a scarce capacity of producing clusters and strong aftershock sequences. The eastern fault systems of our study area are distinguishable in two main distinct systems, which generated two strong seismic sequences in 1997 and 2016–2017. In the former (Colfiorito) sequence the seismicity showed a very low b-value and a modest probability of independence, while in the latter (Central Italy) sequence the b-value was significantly higher and the probability of independence had extremely low values (manifesting a high level of clustering). The much higher b-value of the EFS than the other extensional sources could be caused by its peculiar seismotectonic role of discontinuity at the base of the normal active faulting, and its reduced capacity of accumulating stress. This circumstance may be interpreted by a difference in the rheological properties of these fault systems, possibly also in relation to their present status in the earthquake cycle and the presence of strong aftershock sequences.

The whole story: Rumors and science communication in the aftermath of 2012 Emilia seismic sequence

Controversies that stir the public debate on geological matters usually revolve around a few specific aspects, including the actual trigger of geological phenomena (i.e., natural vs. anthropogenic), their predictability, and the trustworthiness of the experts who provide information and advice on the phenomena. A typical example of such difficulties is the case of the 2012 Emilia, Italy, seismic sequence which struck an area of relatively moderate seismic hazard. In that period, geophysical prospecting was planned to assess the potential of a reservoir for gas storage, near the town of Rivara. The low frequency of important seismic events in the area, associated with the ongoing industrial planning prompted widespread rumors of an anthropogenic origin of the 2012 earthquakes. Controversy also arose about the actual size of the seismic events: earthquakes magnitude can be computed with different methods, and its value depends on the type, number, and geographical distribution of the available seismic stations. As a result, different institutions commonly release different estimates of the earthquake magnitude, casting doubts on the reliability of each estimate. Since 2012, public concern has also been caused by the repeated occurrence of unusual phenomena in the area, such as ground heating or bubbling well waters. Popular belief tends to establish a causal link between particular phenomena and seismic activity, reinforcing the false conviction that seismicity could be predicted. In this work we present and discuss some of the activities that INGV pursued through the years to contrast rumors and disseminate correct scientific information. In the aftermath of the 2012 seismic sequence, INGV worked in collaboration with the National Department of Civil Protection, the local administrations, the University Network of seismic engineering, the Regional Healthcare System and local volunteer organizations. The organization of public meetings, the collection and analysis of widespread rumors and the creation of ad hoc outreach materials all contributed to reinforce the mutual trust between our research institute and the local population.

Numerical Assessment of Interacting Structural Units on the Seismic Damage: A Comparative Analysis with Different Modeling Approaches

The conservation of the historical and artistic heritage is one of the main priorities of Italian and international policy. The great variety of masonry buildings that make up this heritage is characterized by different combinations of materials and construction techniques. Then, several damage scenarios could be observed as a result, requiring appropriate retrofitting interventions. A rather accurate structural behavior analysis, especially for horizontal load conditions, allows for elaborating a correct seismic assessment. Albeit there are various numerical tools available to examine them, each one’s process starts by means of certain assumptions that could not be applied indiscriminately. This paper aims to compare two different types of modeling techniques to evaluate their strengths and weaknesses. To achieve this goal, an earthquake-damaged complex in Central Italy was chosen as a case study. The structure was modeled using a finite element (continuous) and a distinct element (discontinuous) method. Both approaches underwent a nonlinear dynamic analysis using the strong motions recorded during the 2016 seismic sequence. The results show that both approaches can evaluate the weak structural points. However, in some cases, the distinct element method appeared more accurate in reproducing the cracks.

Deposition of cenomanian – Turonian organic-rich units on the mid-Norwegian margin: Controlling factors and regional implications

On the mid-Norwegian margin, extensive rifting and subsequent deposition of thick Cretaceous and Cenozoic sediments have buried the traditional Upper Jurassic organic-rich shales too deep. Consequently, these organic-rich shales are overmature and spent in the deep basins on the mid-Norwegian margin. The absence of well-control, variable seismic quality and in particularly, the great burial depth, makes it difficult to identify alternative Upper Jurassic and Lower Cretaceous organic-rich units. By combining high-resolution 2D seismic data, well logs, and Rock-Eval data, this study documents the presence of alternative organic-rich units in the Cretaceous succession on the Halten Terrace and the Vøring Basin. Multiple seismic horizons which correspond to regional flooding surfaces and define a series of seismic sequences have been mapped across the study area. The regionally extensive upper Cenomanian horizon is associated with wireline log signals and Rock-Eval parameters which imply the presence of a potential source rock unit. Source rock evaluation indicate that this unit contains mainly kerogen Type III on the Halten Terrace, suggesting an organofacies with significant contribution from terrestrial sources. In the Vøring Basin, the unit is sparsely drilled but appears to be mature, thus displaying a relatively limited potential. One well from the Vigrid Syncline demonstrate somewhat higher potential, with Rock-Eval data indicating a kerogen Type II composition. As such, more prolific units seems to exist in the Vøring Basin, albeit exhibiting a patchy distribution. We speculate that the deposition and preservation of this upper Cenomanian organic-rich unit record the development of an extended oxygen minimum zone attributable to increased primary production and sluggish water circulation, linked to the global Oceanic Anoxic Event 2 (OAE 2). However, local physiographic conditions, such as high sedimentation rates, erosion by gravity flows and periodically oxygenated conditions hindered preservation of a significant quantities of organic matter, thus limiting the thickness and quality of the upper Cenomanian organic-rich unit on the mid-Norwegian margin.

Geopolymers-based application for the up-cycling utilization of construction and demolition waste from the 2016 central Italy earthquakes

The 2016 seismic sequence in central Italy produced huge amounts of rubble. The need to recycle construction and demolition waste (CDW) to facilitate reconstruction process is therefore a problem of highest concern for quantities involved. In addition, CDW from rubble is very difficult to recycle being an extremely heterogeneous material.In this study, in order to produce mortars, the complete replacement of natural aggregate was investigated using the finest as-received CDW (0–8 mm) produced by local plants that managed the 2016 earthquake rubble.Results revealed that samples containing 60 wt.% CDW, metakaolin as precursor and K-silicate as alkaline reagent, have mechanical properties up to 28.7 MPa and mostly in the range of structural ordinary cementitious materials, suggesting that even the CDW fine fractions could be used in the production of upcycling mortars.

Seismic stratigraphy and development of a modern isolated carbonate platform (Xuande Atoll) in the South China Sea

Xuande Atoll is an isolated carbonate platform that has developed since the early Miocene. This study conducted high-resolution seismic surveys and shallow drilling to understand its internal structure and development. Five seismic sequences were observed (from bottom to top): SQ1 (early Miocene), SQ2 (middle Miocene), SQ3 (late Miocene), SQ4 (Pliocene), and SQ5 (Quaternary). The seismic data indicated that the platform formation started in the early Miocene and flourished during the early and middle Miocene. The platform shrank before the isolated platform formed in the middle Miocene. The final shrinking stage occurred in the southern and western parts of the platform at the end of the Miocene, which may reflect rapid tectonic subsidence and increased terrigenous sediment inputs owing to the formation of the semi-marginal sea. The peri-platform contains a falling sea-level sequence that was dominated by mass wasting deposits.

Fault and Fluid Interaction during the 2012 Emilia (Northern Italy) Seismic Sequence

AbstractThe triggering of large earthquakes by anthropic activities is a challenging issue in seismology, invoked also for the ML 5.9 and 5.8 Emilia 2012 destructive earthquakes. The interaction between the two earthquakes that propagated along adjacent thrusts is still an open issue. In this study, we used waveform cross correlation and double-difference (DD) location methods to precisely relocate the aftershock sequence and get insights into fault geometry, structure, and rheology by means of DD seismic tomography. Accurate relocations highlight a complex fault system with small-length fault segments coalescing in the Mirandola and Ferrara thrusts. We observe a broad continuous high-VP/VS anomaly at seismogenic depth (about 6.0 km) that suggests a possible hydraulic connection along the entire fault system. A close look at seismicity indicates a quasi-simultaneous activation of the entire thrust system, with the two mainshocks and large aftershocks occurring within the high-VP/VS, high fluid pressure, and connecting volume.

A note on peak inelastic displacement as a proxy for structural damage in seismic sequences

Structural reliability assessment for a building that may experience damage accumulation during a seismic sequence can play an important role in decision making for post-earthquake repair operations or demolition and rebuilding. This typically requires the integration of the aftershock ground motion hazard at the site with the probabilistic description of the damaged building's capacity to withstand the shaking of the seismic sequence. This is usually quantified as the conditional probability that the structure, starting from a specific damage state and for given shaking intensity, will reach a more severe one. In sequence-based seismic risk studies, an analytically-derived estimate of the peak inelastic displacement is often used as a proxy for structural damage. This paper investigates the issues behind this choice and the ability of inelastic displacement demand to adequately describe structural damage due to a seismic sequence, when compared with more direct metrics of damage, such as stiffness and strength degradation. To reach this objective, a series of inelastic single-degree-of-freedom systems, having different natural period, backbones and post-elastic behavior, were subjected to sequential dynamic analysis, while considering a series of arbitrarily chosen damage states, conventionally defined by displacement demand thresholds. The investigation showed that maintaining the attractive simplicity of deformation-based damage proxies in sequence-based risk analysis, can lead to some counterintuitive representations of seismic vulnerability. Some results suggest that such problems could be alleviated if one were to consider some dependence of damage state transition thresholds on the current state of the structure.

Effectiveness of traditional strengthening measures on historic masonry buildings: the seismic performance of Palazzo Comunale in Camerino after 2016-2017 seismic sequence

The implementation of seismic strengthening measures on monumental buildings requires a balance between the need to preserve its original configuration and the need to guarantee adequate safety levels. The paper presents the analysis of the performance of a heritage building in Camerino, a small town in central Italy, after the 2016-2017 seismic sequence.The building is called Palazzo Comunale, a medieval building, used as town hall. Due to the previous earthquake occurred in 1997, the Palazzo Comunale suffered extensive damage; repairs and strengthening measures were designed and realized starting from 1999. In particular, traditional strengthening techniques were adopted: the mechanical characteristics of the walls were improved by means of grout injections, the original wooden floors were either replaced or stiffened, and several steel tie rods were introduced.In situ surveys allowed to detect the damage caused by the 2016 seismic sequence and to evaluate the effectiveness of the strengthening measures in improving the seismic behavior of the Palazzo Comunale. Furthermore, the seismic vulnerabilities of the buildings are herein discussed through global non-linear static analyses and local kinematic analyses.

SHM of historical buildings: The case study of Santa Maria in Via church in Camerino (Italy)

Historical buildings constitute a huge heritage for the Italian country, and they deserve to be preserved to be handed over in good condition for future generations. As well know, Italy is a prone earthquake country and many earthquakes occurred over time producing awful consequences in terms of human losses and building damage. Historical buildings are typically the most damaged ones since they were built often with poor materials and conceived to sustain only gravitational loads. The preservation of these buildings is not a trivial task as structural retrofits have to be carried out not only in a proper way, but also timely in case the actual conditions of the construction may worse over time. Since large-scale rapid interventions after an earthquake are almost impossible, instrumenting damaged structures with appropriate sensors and analyzing measured data become crucial to control the damage evolution. At the same time, the monitoring of secured structures is essential to evaluate the effectiveness of the interventions and the possible evolution of damage. This paper presents the Structural Health Monitoring (SHM) system installed in the Santa Maria in Via church in Camerino (Central Italy). The church, severely damaged after the seismic sequence that stroke Central Italy in 2016, was secured with a steel structural system aimed at preventing possible collapse of some peculiar components, as the overturning of the massive façade body and the collapse of the slender elliptical drum. The SHM system permanently installed is presented; the latter consists of several sensors of different typologies placed in specific positions to monitor the effectiveness of the securing steel structure and the behavior of the church. Also, the Optimal Sensor Placement (OSP) methodology is adopted to determine the best sensor layout (number and position) to develop the SHM of the case study. Finally, the numerical model developed to support the interpretation of the SHM data, is described.

Effect of ground-motion sequences on a unreinforced masonry wall restrained by an elasto-plastic tie-rod

This work investigates the effect of international ground-motion sequences on the out-of-plane response of an ordinary-building façade. The following assumptions are made on the wall boundary conditions: the wall is resting on a foundation, it is adjacent to transverse walls and restrained by elasto-plastic tie rods with finite elongation capacity. Four walls are considered of different aspect ratio and size; two types of masonry are assumed, and the tie is designed following a force-based procedure according to the Commentary to the Italian Building Code. The walls are modelled as rigid blocks of finite thickness and free to rotate on one side only. The rocking response of the walls, excited in the out-of-plane direction under 56 sequences of records, is evaluated. The effect of sequences is estimated by the comparison of the response experienced during the sequence and under a single record, strongest in terms of either peak ground acceleration or velocity. Finally, in order to reduce the vulnerability originated by a seismic sequence, a proposal of a reduced behaviour factor to be adopted in the design of tie rods is formulated.

Exceedance of design seismic actions during the 2016-2017 central Italy seismic sequence: sensitivity to two seismic hazard models

In Italy, seismic ground motion intensity for structural design relies on probabilistic seismic hazard analysis (PSHA). Research has shown that, even in the case of a moderate magnitude earthquake, it is expected that ground motion intensities larger than the design counterparts are observed at some sites in the epicentral region. The area where such an exceedance has possibly occurred can be assessed via ShakeMap. In the case of seismic sequences, ShakeMap envelopes allow to identify the fraction of the region of interest subjected to at least one exceedance of design seismic actions. For the 2016-2017 central Italy sequence, ShakeMap envelopes reveal that exceedance of the design intensity enforced by the current building code occurred in an area covering thousands of square kilometers, depending on the spectral and exceedance return period of the design intensity. This study quantifies the exceedance area of ground motion intensity according to the PSHA results based on two alternative PSHA models for Italy. One is that at the basis of the official PSHA for Italy adopted by the current building code, known as MPS04; the other relies on a grid-seismicity source model deriving from a set of source models recently developed for a new PSHA study for the country (MPS19). Looking at ShakeMap envelopes, it is found that the estimated exceedance area is of the same order of magnitude for the two hazard models, at least for the spectral and exceedance return periods considered herein.

Observational loss database of typological precast RC buildings damaged after the 2012 Emilia Earthquake

The Emilia Earthquake occurred in 2012 in a highly industrialized area, characterized by the presence of about one firm every 9 inhabitants. The industrial heart of the region hosts many important clusters, from the Motor Valley to Food, Wellbeing, Fashion and Health devices. The main activities are conducted in production districts with several different long-span buildings like storages, deposits, warehouses, factories and silos. Among these, those made of precast reinforced-concrete (RC) elements were heavily damaged by the seismic sequence, resulting in a huge amount of economic losses due to damage to structures, products and machineries, business interruption and casualties. In the aftermath of the earthquake, the Region defined the criteria for the request of funds for the reconstruction of the buildings, the restoration of the products, the reparation of the equipment, and the temporary relocation of the activities. Thus, a large number of documents was collected reporting a variety of information concerning the seismic damage, the structural properties of the buildings, and the economic costs.In this work, through a process of progressive selection and refinement of the data, a database of seismic economic losses of damaged precast RC buildings was created. The main principles for the creation of the repository and the categorization of the information are illustrated. Hence, the losses were statistically analysed to derive useful consequence functions based on the investigation of diversified trends of the repair costs at different damage levels. The outcomes presented in this study may be adopted to perform loss assessment evaluations to guide the decision-makers in establishing priorities of structural interventions to reduce the consequences of future earthquakes in industrial areas.

Assessment of the effect of seismic sequences on steel X-CBF for industrial buildings

This work concerns about the study of the effect of the seismic sequences on steel mono-storey industrial buildings equipped with X-CBFs, with the aim to evaluate a code change to adequately consider this issue. Indeed, current technical regulations (CEN, 2004; MIT, 2018) do not take into account this phenomenon, thus the structure are designed only to withstand a single main-shock, without considering the possible accumulation of damage due to the after-shocks. In this work it is instead shown how this effect has to be properly considered and evaluated. First, a mono-storey industrial building is analysed as preliminary case study. Fragility curves are built for both sequences and single main events, thus obtaining an important comparison. Then the study focuses on a single X-CBF, validated through an experimental test from literature. The calibrated system is subjected to both seismic sequences and corresponding mainshocks. Analyses are carried out also by varying brace profiles. The results show a significant influence of the seismic sequences on the increase of the ductility request of the structure. Therefore, with the aim to properly represent the effect of the sequences, it is considered necessary to require a reduction of the available behavior factor, providing a precautionary estimate. This operation wants to give a first preliminary estimate of the increase of the seismic risk only on the seismic vulnerability side of this kind of structures.

Push ‘o ver: a pushover test program on an existing brickwork construction

An experimental pushover was carried on two very similar unreinforced masonry constructions. These constructions were obtained from an existing two-story brickwork building, located at Castel di Lama and to be demolished due to the damage suffered during the seismic sequence that affected central Italy from August 2016 to January 2017. The central stairwell was demolished in a controlled manner and, thanks to the symmetry of the original building, two almost identical portions were delivered: one was simply repaired, by repointing the cracks caused by the earthquakes, the other was seismically strengthened using Fibre Net reinforced plaster or composite reinforced mortar. The plaster was applied on both faces of the load-bearing walls of the first level and only on the external face at the second level. Preliminary dynamic characterization tests were carried out on both constructions. Then, pushover tests were carried out until collapse on both portions, using a steel structure placed on a reinforced concrete mat supported by four piles, which allowed to apply increasing horizontal forces at the two floors. The experimental results were analysed carefully and compared with those obtained from suitable numerical models.

The Application of Stochastic Seismic Inversion Method of Geostatistical Inversion in Putaohua X Area

Stochastic seismic inversion is an important part of geostatistical inversion method, and is the combination of seismic inversion and sequence simulation. In the process of random seismic inversion, firstly, the histogram distribution of random variables is counted, the variation function of random variables is calculated, and the variation range of random variables in different directions is determined. Then, for each implementation, the seismic traces are synthesized at the seismic channel position according to the calculated reflection coefficient, and the error between the synthetic traces and the original seismic traces is compared, and the inversion results are output after the required accuracy is reached. Geostatistical inversion can improve the vertical and horizontal resolution of the reservoir and accurately describe the spatial distribution of the reservoir. Taking the Heidimiao oil layer in the west slope area of Daqing Placanticline as an example, this paper expounds the application of geostatistical inversion in the work area as a whole. Combined with the results of seismic attribute analysis and well logging curve preprocessing, the inversion results formed by accurate time-depth calibration and other processes of reservoir sensitivity parameter analysis provide a basis for optimizing the target well location in the work area.

A Seismic Facies Analysis to Determine the Relative Age and History of the Al Idrissi Mud Volcano from Offshore Larache Located in the NW Moroccan Atlantic Margin

Formed on top of the Gulf of Cadiz, the Al Idrissi mud volcano is the shallowest and largest mud volcano in the El Arraiche mud volcano field of the northwestern Moroccan margin. The development and morphology of mud volcanoes from the El Arraiche mud volcanoes group have been studied at a large scale. However, the time interval related to their formation period still needs to be better understood. In this regard, we interpreted and analyzed the seismic facies from the 2D reflection data of the GEOMARGEN-1 campaign, which took place in 2011. The aim was to identify the seismic sequences and draw the Al Idrissi mud volcano system to determine the formation period of the Al Idriss mud volcano. And as a result, the Al Idrissi mud volcano system is made of both buried and superficial bicone and was identified along with the Upper Tortonian to Messinian-Upper Pliocene facies. As the initial mud volcano extrusive edifice, the buried bicone was formed in the Late-Messinian to Early-Pliocene period. However, the superficial bicone, as the final extrusive edifice, was included in the Late Pliocene. In this case, the timing interval between the buried and superficial bicone is equivalent to the Late-Messinian to Upper-Pliocene period. Therefore, the latter corresponds to the Al Idrissi mud volcano formation period.

Operational critical issues filling in the Italian form for the post-earthquake damage assessment of churches (A-DC 2006)

In the emergency phase following a severe seismic event, it is essential to quickly proceed with the assessment of the damage suffered by buildings, both to assess which structures are still usable and to promptly intervene on damaged structures in order to prevent them from further damage. Damage data is also very important for the scientific community as it allows the creation of fragility curves for groups of buildings with homogeneous vulnerability and to carry out risk mitigation strategies. The Department of Italian Civil Protection has developed, for each type of building (residential buildings, long-span buildings, churches, historic buildings), survey forms to collect the damage reported by the structures in a standardized way.This paper is focused on the form used for churches (A-DC2006 form), that analyzed the seismic behavior of a church by considering each macro-element that composes it independently (i.e., façade, nave, apse, transept ...). The form proposes for each macro-element a variable number of collapse mechanisms, for a total of 28.The analyses presented here concern the data of 225 churches inspected during the 2016-2017 Central Italy seismic sequence. All the churches were investigated twice by different technicians due to the occurrence of a second seismic event that required a further inspection. This chance has allowed to compare the data of two inspections relating to the same church and it highlighted the presence of frequent interpretative differences: often the collapse mechanisms identified by one technician did not coincide with those identified by the other technician. Each of the 225 churches was therefore carefully analyzed to identify the recurring situations that caused these critical issues.

Preliminary results in the automated detection of operational modal properties of the Portico Varano in the Camerino Ducal Palace

Portico Varano in the Ducal Palace of Camerino (Italy) is a renaissance monumental quadriporticus that was damaged by the 2016 Central Italy seismic sequence. Within the field activities for saving cultural heritage foreseen within a recent European research project named ARCH, a long-term monitoring system, comprising different types of sensors, such as accelerometers, displacement transducers, environmental sensors, and a weather station, was set up to achieve comprehensive measures of its operational behaviour and the evolution of the damage. The monitoring system, installed in October 2020, is currently operating, providing valuable information on the experimentally observed dynamic behaviour, also considering changes in the environmental conditions.Starting from the results of the dynamic characterization of the structure and after the optimization of the position of the sensors, this paper shows and discusses the efforts made to track over time the modal characteristics of the Portico Varano in order to detect changes in its conditions. In addition, a procedure has been proposed and implemented combining information available from Italian National Institute of Geophysics and Volcanology (INGV) to identify recorded data related to seismic events relevant to operational conditions.