Modeling the Observed Site Response from Istanbul Strong Motion Network

An extensive site investigation study was carried out in the European side of Istanbul as part of the large-scale microzonation project for the Istanbul Metropolitan Municipality. 2912 borings mostly down to 30m depth with approximately 250m spacing were conducted within an area of 182 sqkm to investigate local site conditions. 55 stations of the Istanbul Rapid Response Network and Ataköy vertical array are located in this area. There have been few small earthquakes in the recent years with local magnitude slightly over M=4. One of these earthquakes took place on 12/3/2008 in Yalova with local magnitude of M=4.8. Vertical array stations at 4 levels (ground surface, at depths of 50m, 75m and 140m) and 23 of the 55 Istanbul Rapid Response Network stations recorded this earthquake. Based on the recorded acceleration time histories on the engineering bedrock at Ataköy vertical array, the remaining recorded acceleration time histories are modeled based on empirical site amplification relationships proposed by Borcherdt (1994) and based on a modified version of Shake91 (Idriss and Sun, 1992). An attempt is also made to model the recorded acceleration time histories during the Mw=7.4, 1999 Kocaeli Earthquake recorded at Ataköy, Fatih and Zeytinburnu stations located in the same area

LZER0: A Cost-Effective Multi-Purpose GNSS Platform

Recent advances in Global Navigation Satellite System (GNSS) technology have made low-cost sensors available to the mass market, opening up new opportunities for real-time ground deformation and structure monitoring. In this paper, we present a new product developed in this framework by the National Institute of Oceanography and Applied Geophysics–OGS in collaboration with a private company (SoluTOP SAS): a cost-effective, multi-purpose GNSS platform called LZER0, suitable not only for surveying measurements, but also for monitoring tasks. The LZER0 platform is a complete system that includes the GNSS equipment (M8T single-frequency model produced by u-blox) and the web portal where the results are displayed. The GNSS data are processed using the RTKLIB software package, and the processed results are made available to the end user. The relative positioning mode was adopted both with real-time and post-processing RTKLIB engines. We present three applications of LZER0—cadastral, monitoring, and automotive—which demonstrate that it is a flexible, multi-purpose platform that is easy to use in terms of both hardware and software, and can be easily deployed to perform various tasks in the research, educational, or professional sectors

GFZ Wireless Seismic Array (GFZ-WISE), a Wireless Mesh Network of Seismic Sensors: New Perspectives for Seismic Noise Array Investigations and Site Monitoring

Over the last few years, the analysis of seismic noise recorded by two dimensional arrays has been confirmed to be capable of deriving the subsoil shear-wave velocity structure down to several hundred meters depth. In fact, using just a few minutes of seismic noise recordings and combining this with the well known horizontal-to-vertical method, it has also been shown that it is possible to investigate the average one dimensional velocity structure below an array of stations in urban areas with a sufficient resolution to depths that would be prohibitive with active source array surveys, while in addition reducing the number of boreholes required to be drilled for site-effect analysis. However, the high cost of standard seismological instrumentation limits the number of sensors generally available for two-dimensional array measurements (i.e., of the order of 10), limiting the resolution in the estimated shear-wave velocity profiles. Therefore, new themes in site-effect estimation research by two-dimensional arrays involve the development and application of low-cost instrumentation, which potentially allows the performance of dense-array measurements, and the development of dedicated signal-analysis procedures for rapid and robust estimation of shear-wave velocity profiles. In this work, we present novel low-cost wireless instrumentation for dense two-dimensional ambient seismic noise array measurements that allows the real–time analysis of the surface-wavefield and the rapid estimation of the local shear-wave velocity structure for site response studies. We first introduce the general philosophy of the new system, as well as the hardware and software that forms the novel instrument, which we have tested in laboratory and field studies

Fingerprint Identification Using Noise in the Horizontal-to-Vertical Spectral Ratio: Retrieving the Impedance Contrast Structure for the Almaty Basin (Kazakhstan)

Detailed knowledge of the 3D basin structure underlying urban areas is of major importance for improving the assessment of seismic hazard and risk. However, mapping the major features of the shallow geological layers becomes expensive where large areas need to be covered. In this study, we propose an innovative tool, based mainly on single station noise recordings and the horizontal-to-vertical spectral ratio (H/V), to identify and locate the depth of major impedance contrasts. The method is based on an identification of so-called fingerprints of the major impedance discontinuities and their migration to depth by means of an analytical procedure. The method is applied to seismic noise recordings collected in the city of Almaty (Kazakhstan). The estimated impedance contrasts vs. depth profiles are interpolated in order to derive a three-dimensional (3D) model, which after calibration with some available boreholes data allows the major tectonic features in the subsurface to be identified

Towards specific T–H relationships: FRIBAS database for better characterization of RC and URM buildings

FRIBAS database is an open access database (https://doi.org/10.5281/zenodo.6505442) composed of the characteristics of 312 buildings (71 masonry, 237 reinforced concrete and 4 mixed types). It collects and harmonizes data from different surveys performed on buildings in the Basilicata and Friuli Venezia Giulia regions (Southern and Northeastern Italy, respectively). Each building is defined by 37 parameters related to the building and foundation soil characteristics. The building and soil fundamental periods were experimentally estimated based on ambient noise measurements. FRIBAS gave us the opportunity to study the influence of the main characteristics of buildings and the soil-building interaction effect to their structural response. In this study, we have used the FRIBAS dataset to investigate how the building period varies as a function of construction materials and soil types. Our results motivate the need of going beyond a ‘one-fits-all’ numerical period–height (T–H) relationship for generic building typologies provided by seismic codes, towards specific T–H relationships that account for both soil and building typologies

Monitoring the Microseismicity through a Dense Seismic Array and a Similarity Search Detection Technique: Application to the Seismic Monitoring of Collalto Gas-Storage, North Italy

Seismic monitoring in areas where induced earthquakes could occur is a challenging topic for seismologists due to the generally very low signal to noise ratio. Therefore, the seismological community is devoting several efforts to the development of high-quality networks around the areas where fluid injection and storage and geothermal activities take place, also following the national induced seismicity monitoring guidelines. The use of advanced data mining strategies, such as template matching filters, auto-similarity search, and deep-learning approaches, has recently further fostered such monitoring, enhancing the seismic catalogs and lowering the magnitude of completeness of these areas. In this framework, we carried out an experiment where a small-aperture seismic array was installed within the dense seismic network used for monitoring the gas reservoir of Collalto, in North Italy. The continuous velocimetric data, acquired for 25 days, were analysed through the application of the optimized auto-similarity search technique FAST. The array was conceived as a cost-effective network, aimed at integrating, right above the gas storage site, the permanent high-resolution Collalto Seismic Network. The analysis allowed to detect micro-events down to magnitude Ml = −0.4 within a distance of ~15 km from the array. Our results confirmed that the system based on the array installation and the FAST data analysis might contribute to lowering the magnitude of completeness around the site of about 0.7 units

Coordinated and Interoperable Seismological Data and Product Services in Europe: the EPOS Thematic Core Service for Seismology

In this article we describe EPOS Seismology, the Thematic Core Service consortium for the seismology domain within the European Plate Observing System infrastructure. EPOS Seismology was developed alongside the build-up of EPOS during the last decade, in close collaboration between the existing pan-European seismological initiatives ORFEUS (Observatories and Research Facilities for European Seismology), EMSC (Euro-Mediterranean Seismological Center) and EFEHR (European Facilities for Earthquake Hazard and Risk) and their respective communities. It provides on one hand a governance framework that allows a well-coordinated interaction of the seismological community services with EPOS and its bodies, and on the other hand it strengthens the coordination among the already existing seismological initiatives with regard to data, products and service provisioning and further development. Within the EPOS Delivery Framework, ORFEUS, EMSC and EFEHR provide a wide range of services that allow open access to a vast amount of seismological data and products, following and implementing the FAIR principles and supporting open science. Services include access to raw seismic waveforms of thousands of stations together with relevant station and data quality information, parametric earthquake information of recent and historical earthquakes together with advanced event-specific products like moment tensors or source models and further ancillary services, and comprehensive seismic hazard and risk information, covering latest European scale models and their underlying data. The services continue to be available on the well-established domain-specific platforms and websites, and are also consecutively integrated with the interoperable central EPOS data infrastructure. EPOS Seismology and its participating organizations provide a consistent framework for the future development of these services and their operation as EPOS services, closely coordinated also with other international seismological initiatives, and is well set to represent the European seismological research infrastructures and their stakeholders within EPOS.info:eu-repo/semantics/publishedVersio

Application of Surface wave methods for seismic site characterization

Surface-wave dispersion analysis is widely used in geophysics to infer a shear wave velocity model of the subsoil for a wide variety of applications. A shear-wave velocity model is obtained from the solution of an inverse problem based on the surface wave dispersive propagation in vertically heterogeneous media. The analysis can be based either on active source measurements or on seismic noise recordings. This paper discusses the most typical choices for collection and interpretation of experimental data, providing a state of the art on the different steps involved in surface wave surveys. In particular, the different strategies for processing experimental data and to solve the inverse problem are presented, along with their advantages and disadvantages. Also, some issues related to the characteristics of passive surface wave data and their use in H/V spectral ratio technique are discussed as additional information to be used independently or in conjunction with dispersion analysis. Finally, some recommendations for the use of surface wave methods are presented, while also outlining future trends in the research of this topic

On the Limitations of Spectral Source Parameter Estimation for Minor and Microearthquakes

Reliable estimation of earthquake source parameters is fundamental to improve our understanding of earthquake source physics and for ground‐motion modeling in seismic hazard assessment. Nowadays, methods traditionally used for investigating the source parameters of earthquakes with Mw M w ≥3, such as spectral fitting or spectral ratio approaches, are also extensively applied to smaller magnitude events because of the increase in the number of stations and the more common borehole installations. However, when working with recordings of such minor and microearthquakes, significant limitations of the usable frequency range spanned by the spectra arise. At the lower end, signal‐to‐noise ratio constraints limit the usage of low frequencies, whereas at the upper end, the sampling rates of typical seismological networks as well as high‐frequency attenuation can be limiting factors. In addition, earthquake source parameters determined from ground‐motion spectra are known to exhibit potentially serious trade‐offs, in particular the corner frequency and high‐frequency attenuation. In this study, we go beyond the typical discussion of these trade‐offs using simplistic spectral models by investigating the impact of the background wave propagation model on the source parameter trade‐offs as well as its effect on the feasibility of obtaining useful source parameters by means of spectral fitting for minor and microevents. The analysis takes advantage of ad hoc simulated synthetic seismograms with well‐defined underlying background propagation models and considers increasing complications in these models (intrinsic and scattering attenuation). The results show that with given realistic background models and usable frequency bands, the source parameter estimation for minor and microevents can be significantly biased, and not surprisingly, this bias is mainly affecting the estimation of the corner frequency. We highlight the inherent limitations of joint spectral fitting approaches for the determination of source parameters from minor and microearthquakes, which should always be viewed with great caution when physically interpreted