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An innovative fiber-optic hydrophone (FOH) was developed and investigated via an experiment at sea; it is capable of operating at a very low frequency of the seismic spectrum and detecting small magnitude earthquakes. The FOH exploits an optical fiber coil wrapped around a sensitive mandrel in a Michelson interferometric configuration. The FOH operated for about seven days at a water depth of 40 m, in the Campi Flegrei volcanic area (Southern Italy), and a few meters from a well-calibrated PZT hydrophone used as a reference. Thirty-three local earthquakes occurred during the simultaneous operation of the two hydrophones, allowing a straightforward comparison of the recordings. The local earthquakes occurred at an epicentral distance less than 2.5 km from the site of recording, and were estimated to be in the range of magnitude from −0.8 to 2.7. The analysis of the recorded earthquake waveforms in the frequency and time domains allowed retrieving the response function of the FOH in the frequency range from 5 to 70 Hz. The FOH responsivity in terms of acoustic pressure reached about 230 nm/Pa and was flat in the studied frequency range. Due to the high quality of the FOH recordings, this equipment is suitable for applications addressing submarine volcanic activity and the background seismicity of active faults in the ocean.

Archived seismograms recorded in the 20th century present a valuable source of information for monitoring earthquake activity. However, old data, which are only available as scanned paper-based images should be digitised and converted from raster to vector format prior to reuse for geophysical modelling. Seismograms have special characteristics and specific featuresrecorded by a seismometer and encrypted in the images: signal trace lines, minute time gaps, timing and wave amplitudes. This information should be recognised and interpreted automatically when processing archives of seismograms containing large collections of data. The objective was to automatically digitise historical seismograms obtained from the archives of the Royal Observatory of Belgium (ROB). The images were originallyrecorded by the Galitzine seismometer in 1954 in Uccle seismic station, Belgium. A dataset included 145 TIFF images which required automatic approach of data processing. Software for digitising seismograms are limited and many have disadvantages. We applied the DigitSeis for machine-based vectorisation and reported here a full workflowof data processing. This included pattern recognition, classification, digitising, corrections and converting TIFFs to the digital vector format. The generated contours of signals were presented as time series and converted into digital format (mat files) which indicated information on ground motion signals contained in analog seismograms. We performed the quality control of the digitised traces in Python to evaluate the discriminating functionality of seismic signals by DigitSeis. We shown a robust approach of DigitSeis as a powerful toolset for processing analog seismic signals. The graphical visualisation of signal traces and analysis of the performed vectorisation results shown that the algorithms of data processing performed accurately and can be recommended in similar applications of seismic signal processing in future related works in geophysical research.

The horizontal-to-vertical spectral ratio (HVSR) has been extensively used in site characterization utilizing recordings from microtremor and earthquake in recent years. This method is proposed based on ground pulsation, and then it has been applied to both S-wave and ambient noise, accordingly, in practical application also different. The main applications of HVSR are site classification, site effect study, mineral exploration, and acquisition of underground average shear-wave velocity structure. In site response estimates, the use of microtremors has been introduced long ago in Japan, while it has long been very controversial in this research area, as there are several studies reporting difficulties in recognizing the source effects from the pure site effects in noise recordings, as well as discrepancies between noise and earthquake recordings. In practice, the most reliable way is the borehole data, and the theoretical site response results were compared with the HVSR using shear wave to describe site response. This paper summarizes the applications of the HVSR method and draws conclusions that HVSR has been well applied in many fields at present, and it is expected to have a wider application in more fields according to its advantages.

After the M = 7.0 Haiti earthquake in 2010, many teams completed seismic risk studies in Port-au-Prince to better understand why this not extraordinarily strong event had induced one of the most severe earthquake disasters in history (at least in the Western World). Most highlighted the low construction quality as the main cause for the disaster, but some also pointed to possible soil and topographic amplification effects, especially in the lower and central parts of Port-au-Prince (e.g., close to the harbor). However, very detailed local studies of such site effects have not been completed yet. A Belgian-Haitian collaboration project was established in order to develop a detailed local seismic hazard study for Gros-Morne hill located in the district of Pétion-Ville, southeast of Port-au-Prince. In order to have a better understanding of the amplification on the Gros-Morne hill, in the southeastern part of Port-au-Prince, site effects were investigated by using near surface geophysical methods. The horizontal to vertical spectral ratio technique was applied to ambient vibrations and earthquake data, and multichannel analysis of surface waves and P-wave refraction tomography calculation were applied to seismic data. Standard spectral ratios were computed for the S-wave windows of the earthquake data recorded by a small temporary seismic network. Electrical resistivity tomography profiles were also performed in order to image the structure of the subsurface and detect the presence of water, if any. The spectral ratio results generally show low to medium (1.5–6) resonance amplitudes at one or several different resonance frequencies (for the same site), between 0.5 and 25 Hz. At most of the investigated sites, the fundamental resonance frequency varies between 7 and 10 Hz. By using the multichannel surface wave analyses of the seismic data, we were able to determine shear wave velocities ranging between 200 and 850 m/s, up to a depth of about 15–20 m. From the refraction analysis, we were able to delineate P-waves velocities of 500 to 1500–2000 m/s at the studied sites. The outputs were locally compared with the resistivity data from the electrical profiles. Thus, the overall data indicate a moderate site effect at Gros-Morne hill, with a great variability in site amplification distribution. Initial estimates of local site effects were made on the basis of those outputs and the earthquake recordings. Our results are finally discussed with respect to outputs and interpretations that had been published earlier for the same site. Those results only partly confirm the strong seismic amplification effects highlighted by previous papers for this hill site, which had been explained by the effects of the local topographic and soil characteristics.

Engineering practitioners do not usually include soil-structure interactions in building design; rather, it is common to model and design foundations as embedded joints with joint–based reactions. In some cases, foundation structures are modeled as rigid bodies, embedding the first story into lower vertical elements. Given that the effects of underground floors on the seismic response are not generally included in current building design provisions, it has been little explored in the literature. This work compares and analyzes models to study the effects of different underground stories modeling approaches using earthquake vibration data recorded for the 16–story Alcazar building office in downtown Viña del Mar (Chile). The modeling expands beyond an embedded first story structure to soil with equivalent springs, representing soil-structure interaction (SSI), with varying rigid soil homogeneity. The building was modeled in a finite element software considering only dead load as a static load case because the structure remained in the framing stage when the monitoring system was operating. The instruments registered 72 aftershocks from the 2010 Maule Earthquake, and this study focused on 11 aftershocks of different hypocenters and magnitudes to collect representative information. The comparisons between empirical records and models in this study showed a better fit between the model and the real vibration data for the models that do consider the SSI using horizontal springs attached to the retaining walls of the underground stories. In addition, it was observed that applying a stiffness reduction factor of 0.7 to all elements in deformation verification models for average-height buildings was suitable to analyze the behavior under small earthquakes; better results are obtained embedding the structure in the foundation level than embedding in the street level; the use of horizontal springs with Kuesel’s model with traction for the analysis of the structure yields appropriate results; it is necessary to carefully select the spring constants to be used, paying special attention to the vertical springs. Even though the results presented herein indicate that the use of vertical springs to simulate the SSI of the base slab can result in major differences concerning the real response, it is necessary to obtain more data from instrumentation across a wider variety of structures to continue to evaluate better design and modeling practices. Similarly, further analyses, including nonlinear time-history and high-intensity events, are needed to best regulate building design.

Earthquake wave characterization is essential for better understanding wave propagation phenomena and the description of the local effects produced by the seismic waves. Since seismic events nowadays are recorded using digital electronic recording methods and the seismographs are recorded in digital media such hard disks, CDs, DVDs etc., signal processing methods can be directly used to analyze the properties of the recorded waves. Most seismic recordings are nonstationary so time frequency methods based on well known representations such as the Short-Time Fourier, Choi-Williams and Wavelet are best suited to analyze and process these records. In a near future, the objective is to adapt this innovative joint time-frequency signal processing technique to earthquake record analysis and parameter estimation. [PUBLICATION ABSTRACT]

In this study, accelerometric data from seven Japanese buildings under long-term monitoring were analysed to explore the variability of the buildings’ co-seismic response over time and its within- and between-building components, using co-seismic capacity curves developed in acceleration-displacement-response-spectrum format. The data include the 2011 Tohoku Mw9.1 earthquake, which caused building damage of different levels of severity, and the time-varying actual capacity curves were analysed considering earthquakes before and after 2011. Result showed that the initial slope of the capacity curves reflects the amount of damage. The between-building and within-building components of the variability are discussed by comparing a single building and several buildings in the same class for several earthquakes. Finally, the epistemic uncertainty of seismic risk assessment studies is discussed in relation to the selection of a generic capacity model for all buildings in a single class.

The city of Benevento (Southern Italy) has been repeatedly struck by large historical earthquakes. A heterogeneous geologic structure and widespread soft soil conditions make the estimation of site effects crucial for the seismic hazard assessment of the city. From 2000 until 2004, we installed seismic stations to collect earthquake data over zones with different geological conditions. Despite the high level of urban noise, we recorded more than 150 earthquakes at twelve sites. This data set yields the first, well documented experimental evidence for weak to moderate local amplifications. We investigated site effects primarily by the classical spectral ratio technique (CSR) using a rock station placed on the Benevento hill as reference. All sites in the Calore river valley and in the eastern part of the Benevento hill show a moderate high-frequency (f > 4 Hz) amplification peak. Conversely, sites in the Sabato river valley share weak-to-moderate amplification in a wide frequency band (from 1-2 to 7-10 Hz), without evident frequency peaks. Application of no-reference-site techniques to earthquake and noise data confirms the results of the CSRs in the sites of the Calore river valley and of the eastern part of the Benevento hill, but fails in providing indications for site effects in the Sabato river valley, being the H/V ratios nearly flat. One-dimensional modeling indicates that the ground motion amplification can be essentially explained in terms of a vertically varying geologic structure. High-frequency narrow peaks are caused by the strong impedance contrast existing between near-surface soft deposits and stiff cemented conglomerates. Conversely, broad-band amplifications in the Sabato river valley are likely due to a more complex layering with weak impedance contrasts both in the shallow and deep structure of the valley.[PUBLICATION ABSTRACT]

-- A simple and powerful method for simulating ground motions is to combine parametric or functional descriptions of the ground motion's amplitude spectrum with a random phase spectrum modified such that the motion is distributed over a duration related to the earthquake magnitude and to the distance from the source. This method of simulating ground motions often goes by the name \"the stochastic method.\" It is particularly useful for simulating the higher-frequency ground motions of most interest to engineers (generally, f>0.1 Hz), and it is widely used to predict ground motions for regions of the world in which recordings of motion from potentially damaging earthquakes are not available. This simple method has been successful in matching a variety of ground-motion measures for earthquakes with seismic moments spanning more than 12 orders of magnitude and in diverse tectonic environments. One of the essential characteristics of the method is that it distills what is known about the various factors affecting ground motions (source, path, and site) into simple functional forms. This provides a means by which the results of the rigorous studies reported in other papers in this volume can be incorporated into practical predictions of ground motion.[PUBLICATION ABSTRACT]

PurposeDespite the recurrence of earthquakes, responses are usually triggered afterwards, lacking mitigation strategies to diminish risks. Damaged dwellings cannot be immediately reinforced to continue inhabitation, generating disruption. Repairs are usually costly, as large numbers of affected constructions make damage assessment difficult, and post-earthquake reconstruction programmes often lack a heritage-specific approach. This research seeks to address these issues through a methodology based on high-end documentation technologies applied to built heritage and local community engagement.Design/methodology/approach The methodology proposed combines different recording tools to capture social and built environment data, such as interviews, mapping, drone capture, photography and 3D laser scanning, in the pilot case study of Bela, a historical settlement in the seismic region of Kutch in Gujarat, India, affected by the 2001 Bhuj earthquake. This paper particularly discusses aspects of community engagement around data capture and representation processes.FindingsThe introduction of advanced documentation technologies can help speed up the process of damage assessment, analyse social aspects that are key to a respectful re-construction, and enhance community engagement through visual representations, which are relevant to social acceptance and understanding towards a meaningful introduction and sustained use in earthquake risk management.Research limitations/implicationsThe methodology proposed can inform similar cases in seismic areas and enhance engagement, helping to develop a sense of awareness in the community regarding the need for preparedness in the face of earthquakes. However, there are technical challenges in using advanced recording technologies in terms of equipment accessibility, skills, knowledge and future uses of the data. Social and cultural aspects, such as caste and gender divisions, also implied disparity in accessing the data and relating it to the research team, bringing forward the need to tailor public engagement to achieve inclusivity. Practical implicationsThis study has practical implications. The most relevant one is how the process of carrying out the research served as a way to raise awareness for future seismic events. In this regard, local academic institutions and non-governmental organisations (NGOs) are critical mediators in reaching the community in greater depth, from which to bridge to external and/or governmental agencies based on existing links and trust.Social implicationsThis study also shows social implications. As a case study-based research, the link developed with the local community will help coordinate actions in case an earthquake occurs and increase cohesion within the community towards a joint aim, in this case, to reduce the risk of disasters due to seismic events.Originality/valueThis paper accounts for a novel approach to documenting buildings in heritage settlements prone to earthquakes that uses the digital record as (1) a basis to assess and intervene in the built environment and better understand how it supports the local community’s ways of living and maintaining buildings; and (2) a platform for local engagement and agency in planning and re-construction as a post-disaster mitigation measure.