Passive Seismic Measurements Research Articles

Integrating Seismic Methods for Characterizing and Monitoring Landslides: A Case Study of the Heinzenberg Deep-Seated Gravitational Slope Deformation (Switzerland)

While geodetic measurements have long been used to assess landslides, seismic methods are increasingly recognized as valuable tools for providing additional insights into subsurface structures and mechanisms. This work aims to characterize the subsurface structures of the deep-seated gravitational slope deformation (DSGSD) at Heinzenberg through the integration of active and passive seismic measurements. Seismic techniques can hereby deliver additional information on the subsurface structure and mechanisms involved, e.g., the degree of rock mass degradation, the resonant frequencies of the potentially unstable compartments, and the local fracture network orientations that are influenced by wavefield polarization. By employing advanced methods such as H/V analysis, site-to-reference spectral ratios, polarization analysis, surface wave analysis, and the joint multizonal transdimensional Bayesian inversion of velocity structures, we establish a comprehensive baseline model of the landslide at five selected sites. This baseline model shall help identify potential changes after the refilling of Lake Lüsch, which started in 2021. Our results reveal the rupture surface of the DSGSD at various depths ranging from 30 m at the top to over 90 m in the middle of the slope. Additionally, we estimate key parameters including the shear wave velocities of the different rock masses. The 2D geophysical profiles and rock mass properties contribute to the understanding of the subsurface geometry, geomechanical properties, and potential water pathways. This study demonstrates the significance of integrating seismic methods with traditional geodetic measurements and geomorphologic analysis techniques for a comprehensive assessment of landslides, enhancing our ability to monitor and mitigate hazardous events.

Natural Seismic Event Analysis Based on Signal and Source Characteristics from two Experiments in Antarctica.

This study presents geophysical data from two passive seismic measurements conducted at two different sites in Antarctica. We analyzed the signals mainly in the frequency domain through the multitaper method to extract some spectral characteristics of the signals that would have been out of reach through the usual FFT approach. The power spectral density of the signals carries information about the processes that generated them, allowing its correlation with their source origin and type, either natural or anthropogenic. We deal with three different source types: calving, wind, and anthropogenic origins. The former is closely related to glacier dynamics, being modulated by the prevailing atmospheric processes. At both locations the wind noise is prevalent, complicating the analysis of other events like calving. We have used data classification, estimation of the source azimuth, and seismic apparent velocity to demonstrate the viability of using geophysical methods to study glacier elastic parameters and dynamics. Moreover, the calving rate can yield a wider and more independent understanding of glacier hydrodynamics and may help to estimate the future response of the polar areas to a changing environment.

Rapid estimation of minimum depth-to-bedrock from lidar leveraging deep-learning-derived surficial material maps

Previously glaciated landscapes often share similar surficial characteristics, including large areas of exposed bedrock, blankets of till deposits, and alluvium-floored valleys. These materials play significant roles in geologic and hydrologic resources, geohazards, and landscape evolution; however, the vast extents of many previously glaciated landscapes have rendered comprehensive, detailed field mapping difficult. While recent advances in remote sensing have facilitated mapping of surficial materials and landforms, manual map creation has remained a time-intensive task.The development of convolutional neural networks (CNNs) for image classification has provided a new opportunity for rapid characterization of digital elevation models, thus enabling efficient mapping of surficial materials and landforms. We have developed a methodology that leverages existing geologic maps and high-resolution (1–3 m) lidar data to train a U-Net CNN to classify alluvium and exposed bedrock in previously glaciated regions. Coupled with U.S. Geological Survey-developed geomorphometry tools capable of approximating stream incision depths, these classifications can be used to estimate the minimum thicknesses of stream-proximal hillslope sediments in areas where streams have undergone minimal incision into bedrock.We validate this approach in the context of the Neversink River watershed, a subbasin of the Delaware River Basin and significant water source for New York City. Evaluation of deep learning model performance demonstrates substantial agreement with manually drawn maps of alluvium and exposed bedrock. Validation of the minimum sediment thickness map using borehole data and passive seismic measurements shows the greatest performance for shallow materials and decreased performance in deep sediments, as well as in areas where bedrock exposures were too small to be resolved by lidar. To resolve these issues and create more accurate surficial maps, we are training new CNNs with additional geologic data and exploring advanced approaches for estimating depths of stream incision.

Towards a self-sufficient mobile broadband seismological recording system for year-round operation in Antarctica

Abstract. Passive seismic measurements allow the study of the deeper Earth beneath the thick Antarctic ice sheet cover. Due to logistical and weather constraints, only a fraction of the area of the Antarctic ice sheet can be surveyed with long-term or temporary sensors. A fundamental limitation is the power supply and operation of the instruments during the polar winter. In addition, there is only a limited time window during the field seasons to deploy the stations over the year. Here we present a rapidly and simple deployable self-sufficient mobile seismic station concept. The station consists of different energy supply modules aligned according to the survey needs, measuring duration, and survey aim. Parts of the concept are integrated into an already existing pool of mobile stations and in the seismological network of the geophysical observatory at Neumayer III Station. Other concepts and features are still under development. The overall goal is to use these temporary mobile arrays in regions where little is known about local and regional tectonic earthquake activity.

Seismic Drill-Bit Tracking for Improved Well Positioning

Summary The lateral well position uncertainty of magnetic/gyro measurement-while-drilling (MWD) measurements can often exceed the requirements regarding anticollision, for optimal placement of infill wells between existing producers, or for hitting targets with limited geological extent. The positional uncertainty can be significantly reduced by implementing high-precision drill-bit localization using passive seismic data. Consequently, not only drilling risks can be reduced, but optimal reservoir drainage is ensured as well. By using passive seismic recordings from the seafloor, we can “listen” to the noise generated by the bottomhole assembly (BHA) while drilling. Despite various noise sources in the vicinity (e.g., vessels and rigs), advanced data processing and the combination of hundreds of seafloor receivers spread above the ongoing drilling enable us to detect the drilling signal and locate the drill bit. Whereas the magnetic and gyro MWD tools have errors that accumulate with measured depth (MD), each bit position derived from seismic (usually every 90 seconds) is completely independent. For horizontal sections, the error does not increase with MD and hence can provide improved lateral accuracy. No additional BHA tool is required, and the measurements are neither dependent on the magnetic nor gravitational field. Moreover, the passive seismic measurements can be used to obtain an improved lateral well position estimate. This is done by optimizing the azimuth information of the well trajectory in the minimum curvature method. A lateral uncertainty measure can be derived from the residuals between the passive measurements and the updated well path. Since 2018, we have used the continuous stream of passive data from permanent seafloor sensors at the Grane Field, with its reservoir depth of around 1800 m true vertical depth subsea (TVDSS) to follow all wells with this drill-bit tracking scheme. Lateral deviations from the official well path based on magnetic/gyro measurements are mostly within ±30 m. The lateral position uncertainty can be as low as a couple of meters under optimal conditions.

On the influence of seasonal changes in the resonant properties of surface soils on seismic safety of structures

Field experiments were carried out to assess the possible changes of the seismic safety of buildings due to seasonal variations in the resonant properties of the near-surface soils. The natural frequencies of a ten-storey building and the surface soil layer were determined from passive seismic measurements. The observations were carried out at the end of January when the top soil layer was frozen because of prolonged exposure to negative temperatures, and at the end of June after the ground was completely thawed. The results of the experiments showed that in areas characterized by alternation of long periods of positive and negative temperatures, the natural frequencies of surface soils can change significantly more than the natural frequencies of the buildings built on them. In certain periods, such changes can lead to the coincidence of some natural frequencies of the soil layer and the buildings standing on it, which ultimately reduces the latter seismic safety.

Tectonic Setting of the Kenya Rift in the Nakuru Area, Based on Geophysical Prospecting

In this paper, we present results of tectonic and geophysical investigations in the Kenya Rift valley, in the Nakuru area. We compiled a detailed geological map of the area based on published earlier works, well data and satellite imagery. The map was then integrated with original fieldwork and cross sections were constructed. In key areas, we then performed geophysical survey using Electrical Resistivity Tomography (ERT), Hybrid Source Audio MagnetoTelluric (HSAMT), and single station passive seismic measurements (HVSR). In the study area, a volcano-sedimentary succession of the Neogene-Quaternary age characterized by basalts, trachytes, pyroclastic rocks, and tephra with intercalated lacustrine and fluvial deposits crops out. Faulting linked with rift development is evident and occurs throughout the area crosscutting all rock units. We show a rotation of the extension in this portion of the Kenya rift with the NE–SW extension direction of a Neogene-Middle Pleistocene age, followed by the E–W extension direction of an Upper Pleistocene-Present age. Geophysical investigations allowed to outline main lithostratigraphic units and tectonic features at depth and were also useful to infer main cataclasites and fractured rock bodies, the primary paths for water flow in rocks. These investigations are integrated in a larger EU H2020 Programme aimed to produce a geological and hydrogeological model of the area to develop a sustainable water management system.

Investigation of cliff instability at Għajn Ħadid Tower (Selmun Promontory, Malta) by integrated passive seismic techniques

Għajn Ħadid Tower represents an important cultural heritage of Malta (Central Mediterranean Sea). This tower, built in 1658 on the Selmun Promontory on the northeast coast of the island, was severely damaged by the 1856 Crete earthquake (MW 7.7). The area where the tower ruins stand is involved in a significant landslide process of lateral spreading. During 2015 and 2016, engineering geological surveys and passive seismic measurements were carried out to evaluate the main resonance frequencies of the promontory and monitor the gravity-induced instability process. Seismic ambient noise measurements in the area of the tower show significant horizontal-to-vertical spectral ratio (HVSR) resonance peaks at 3.3–3.5 Hz characterized by linearity and polarization of the particle motion. These features are not present in the measurements carried out on the stable zone and can be related to the vibrational behaviour of the unstable rock block. Additionally, a shear wave velocity profile for the area was obtained by using a seismic array. At the same time, two different approaches were tested for monitoring the landslide process: (i) a Seismic Navigating System (SNS) array detected 20 natural microseismic events caused by the ongoing landslide process; (ii) few-days continuous seismic noise measurements on the unstable rock block were used to carry out a preliminary study of the variation of specific parameters over time.

Deep in a Paleolithic archive: Integrated geophysical investigations and laser-scanner reconstruction at Fumane Cave, Italy

In this paper we used an integrated geomatics and geophysical investigation to gain insight about the Upper Pleistocene Cave deposit of Grotta di Fumane, located near to Verona city, Italy. Geophysical techniques are seldom considered for investigation of Paleolithic sites, mostly because as is typical in such a context, the physical properties of archaeological remains do not possess a clear contrast, with respect to the background and because of their tiny size, are difficult to detect As such, the main goals of this combined survey is to reconstruct the volume of the Paleolithic deposit, in terms of visible geometry, sediments distribution and thickness, and map the morphology of the inaccessible karst bedrock that still await to be excavated. These are achieved by using laser scanning and photogrammetry techniques, to create a three-dimensional digital model of the visible portion and using Electrical Resistivity Tomography (ERT) to map the resistivity distribution in the subsurface. Additionally, single station passive seismic measurements were used to provide an indirect confirmation of the sediments thickness by inverting experimental spectral ratio of microtremors. Geophysical results delivered valuable quantitative information about sediments texture spatial distribution highlighting areas of major archaeological interest. Such information guided the 2014–2017 excavations and continuo providing support for long-term planning of future interventions. Finally, the integrated methodology used in this specific context will lead the way for the use of latest technologies to setup a new prospective for enhanced online visualization and virtual reality for the benefits of both cultural and scientific outreach.

Ice Thickness Estimation from Geophysical Investigations on the Terminal Lobes of Belvedere Glacier (NW Italian Alps)

: Alpine glaciers are key components of local and regional hydrogeological cycles and real-time indicators of climate change. Volume variations are primary targets of investigation for the understanding of ongoing modifications and the forecast of possible future scenarios. These fluctuations can be traced from time-lapse monitoring of the glacier topography. A detailed reconstruction of the ice bottom morphology is however needed to provide total volume and reliable mass balance estimations. Non-destructive geophysical techniques can support these investigations. With the aim of characterizing ice bottom depth, ground-penetrating radar (GPR) profiles and single-station passive seismic measurements were acquired on the terminal lobes of Belvedere Glacier (NW Italian Alps). The glacier is covered by blocks and debris and its rough topography is rapidly evolving in last years, with opening and relocation of crevasses and diffuse instabilities in the frontal sectors. Despite the challenging working environment, ground-based GPR surveys were performed in the period 2016–2018, using 70-MHz and 40-MHz antennas. The 3D ice bottom morphology was reconstructed for both frontal lobes and a detailed ice thickness map was obtained. GPR results also suggested some information on ice bottom properties. The glacier was found to probably lay on a thick sequence (more than 40 m) of subglacial deposits, rather than on stiff bedrock. Week deeper reflectors were identified only in the frontal portion of the northern lobe. These interfaces may indicate the bedrock presence at a depth of around 80 m from the topographic surface, rapidly deepening upstream. Single-station passive seismic measurements, processed with the horizontal-to-vertical spectral ratio (HVSR) method, pointed out the absence of sharp vertical contrast in acoustic impedance between ice and bottom materials, globally confirming the hypotheses made on GPR results. The obtained results have been compared with previous independent geophysical investigations, performed in 1961 and 1985, with the same aim of ice thickness estimation. The comparison allowed us to validate the results obtained in the different surveys, supply a reference base map for the glacier bottom morphology and potentially study ice thickness variations over time.

STABILITY AND SEISMIC VULNERABILITY OF THE STYLITE TOWER AT UMM AR-RASAS

The stability and vulnerability analyses carried out on the Stylite tower at Umm ar−Rasas, Jordan, are presented in this paper. The tower is a unique example of this kind of structure still existing. The soil and the structural material were analyzed by means of in situ ex− perimental tests. These consisted of Schmidt−hammer tests on stone blocks and passive seismic measurements. The stability of the tower was first analyzed, assuming an elastic – perfect plastic behavior in compression for masonry. Then the push−over seismic analysis was carried out, which was based on a single−mode approach and a finite solid element modelling with a Drucker−Prager yield criterion for masonry. The work is propaedeutic to the design of a retrofit intervention.

Shallow bedrock limits groundwater seepage-based headwater climate refugia

Groundwater/surface-water exchanges in streams are inexorably linked to adjacent aquifer dynamics. As surface-water temperatures continue to increase with climate warming, refugia created by groundwater connectivity is expected to enable cold water fish species to survive. The shallow alluvial aquifers that source groundwater seepage to headwater streams, however, may also be sensitive to seasonal and long-term air temperature dynamics. Depth to bedrock can directly influence shallow aquifer flow and thermal sensitivity, but is typically ill-defined along the stream corridor in steep mountain catchments. We employ rapid, cost-effective passive seismic measurements to evaluate the variable thickness of the shallow colluvial and alluvial aquifer sediments along a headwater stream supporting cold water-dependent brook trout (Salvelinus fontinalis) in Shenandoah National Park, VA, USA. Using a mean depth to bedrock of 2.6m, numerical models predicted strong sensitivity of shallow aquifer temperature to the downward propagation of surface heat. The annual temperature dynamics (annual signal amplitude attenuation and phase shift) of potential seepage sourced from the shallow modeled aquifer were compared to several years of paired observed stream and air temperature records. Annual stream water temperature patterns were found to lag local air temperature by ∼8–19 d along the stream corridor, indicating that thermal exchange between the stream and shallow groundwater is spatially variable. Locations with greater annual signal phase lag were also associated with locally increased amplitude attenuation, further suggestion of year-round buffering of channel water temperature by groundwater seepage. Numerical models of shallow groundwater temperature that incorporate regional expected climate warming trends indicate that the summer cooling capacity of this groundwater seepage will be reduced over time, and lower-elevation stream sections may no longer serve as larger-scale climate refugia for cold water fish species, even with strong groundwater discharge.

Site Effects in Archaeoseismic Studies at Mycenaean Tiryns and Midea

The hypothesis that major Mycenaean settlements were devastated by earthquakes at the end of the Late Bronze Age is based on archaeological observations. To test this hypothesis with engineering seismological methods, the local site conditions and their influence on earthquake ground motions should be known. We used active and passive seismic measurements to deduce earthquake site effects at the Mycenaean citadels of Tiryns and Midea in the Argive basin on the eastern Peloponnese. At 182 station locations and with six arrays, we recorded ambient noise data from which Rayleigh‐wave ellipticity curves and dispersion functions were calculated, respectively. In addition, local earthquake data from a nine‐month deployment of 10 stations were used to calculate standard spectral ratios. 1D models were used to calculate amplification functions for the citadels and their surroundings. Although the shallow double limestone knoll of Tiryns, which contained the Mycenaean palace and carries a massive Cyclopean fortification wall, shows only small site amplifications below a factor of 2 at frequencies between 2 and 10 Hz, the soft sediment in the surrounding area where the peasant residences were located has amplifications of 4–6. At the Midea citadel, erected on a 270‐m‐high hill, the topography results in ground‐motion amplifications of a factor of 2–3 at frequencies between 1 and 3 Hz.

Characterization of a complex near-surface structure using well logging and passive seismic measurements

Abstract. We combine geophysical well logging and passive seismic measurements to characterize the near-surface geology of an area located in Hontomin, Burgos (Spain). This area has some near-surface challenges for a geophysical study. The irregular topography is characterized by limestone outcrops and unconsolidated sediments areas. Additionally, the near-surface geology includes an upper layer of pure limestones overlying marly limestones and marls (Upper Cretaceous). These materials lie on top of Low Cretaceous siliciclastic sediments (sandstones, clays, gravels). In any case, a layer with reduced velocity is expected. The geophysical data sets used in this study include sonic and gamma-ray logs at two boreholes and passive seismic measurements: three arrays and 224 seismic stations for applying the horizontal-to-vertical amplitude spectra ratio method (H/V). Well-logging data define two significant changes in the P-wave-velocity log within the Upper Cretaceous layer and one more at the Upper to Lower Cretaceous contact. This technique has also been used for refining the geological interpretation. The passive seismic measurements provide a map of sediment thickness with a maximum of around 40 m and shear-wave velocity profiles from the array technique. A comparison between seismic velocity coming from well logging and array measurements defines the resolution limits of the passive seismic techniques and helps it to be interpreted. This study shows how these low-cost techniques can provide useful information about near-surface complexity that could be used for designing a geophysical field survey or for seismic processing steps such as statics or imaging.

The use of HVSR measurements for investigating buried tectonic structures: the Mirandola anticline, Northern Italy, as a case study

The Mirandola anticline represents a buried fault-propagation fold which has been growing during Quaternary due to the seismogenic activity of a blind segment belonging to the broader Ferrara Arc. The last reactivation occurred during the May 2012 Emilia sequence. In correspondence with this structure, the thickness of the marine and continental deposits of the Po Plain foredeep is particularly reduced. In order to better define the shallow geometry of this tectonic structure, and hence its recent activity, we investigated in a depth range which is intermediate between the surficial morphological observations and seismic profiles information. In particular, we carried out numerous passive seismic measurements (single-station microtremor) for obtaining the horizontal-to-vertical spectral ratio. The results of a combined analysis of the peak frequency and its amplitude nicely fit the available geological information, suggesting that this low-cost geophysical technique could be successfully applied in other sectors of wide morphologically flat alluvial plains to investigate blind and completely buried potential seismogenic structures.

GPR Backscattering Intensity Analysis Applied to Detect Paleochannels and Infilled Streams for Seismic Nanozonation in Urban Environments

Seismic microzonation of urban areas is used to be determined from few soils’ response measurements in each area. In consequence, results can be considered correct only in the case of possible depth-dependent soils, being the existence of lateral soil changes the cause of imprecision. Ground-penetrating radar (GPR) could be a useful tool to determine, previously to the passive seismic measurements, the location of geological structures. Moreover, depending on the ground materials, the GPR energy is randomly backscattered. Consequently, the background noise in the radar scans increases. Therefore, the analysis of the amplitude of the noise could be a useful method to determine changes on the ground characteristics. The analysis of the background GPR amplitude noise is tested in two radar lines, crossing the city of Barcelona. The results show significant differences in the background noise amplitude in the A-scans that could be used to define zones in the city depending on the noise level. These changes on the amplitude are associated with the backscattered energy as a consequence of soil characteristics. Hence, the analysis of the variation in the background noise amplitude allows defining the possible location of subterranean streams, paleochannels, and other structures crossing the plain of the city. Radar results are also compared to ambient vibration measurements, using the spectral horizontal-to-vertical (H/V) quotient, and to historical and contemporary information. The application of the methodology underscores the ability of the evaluation of the backscattering associated with the background noise in the scans in the detection of sharp geological changes in sedimentary deposits.

Finite-difference modeling experiments for seismic interferometry

In passive seismic interferometry, new reflection data can be retrieved by crosscorrelating recorded noise data. The quality of the retrieved reflection data is, among others, dependent on the duration and number of passive sources present during the recording time, the source distribution, and the source strength. To investigate these relations we set up several numerical modeling studies. To carry out the modeling in a feasible time, we design a finite-difference algorithm for the simulation of long-duration passive seismic measurements of band-limited noise signatures in the subsurface. Novel features of the algorithm include the modeling of thousands of randomly placed sources during one modeling run. The modeling experiments explore the dependency relation between the retrieved reflections and source-signature length, source positions, number of sources, and source amplitude variations. From these experiments we observed that the positions of the passive sources and the length of the source signals are of direct influence on the quality of the retrieved reflections. Random amplitude variations among source signals do not seem to have a big impact on the retrieved reflections.

A new hydrostratigraphic model of Venice area (Italy)

Two environmental problems affect the Venice area: subsidence, which has been increasing due to the intensive water abstraction after the Second World War, and contamination of the soil and shallow aquifers. In order to address these problems, which are decisive factors in the entire Venetian ecosystem, the aquifer structure must be known in detail. The lithologic data are abundant and of good quality up to a depth of 50 m, whereas boreholes beyond this depth are much rarer and more dispersed, making their associated lithological data unreliable. This work, which uses the available data together with fast and low cost passive seismic measurements, provides an improved understanding of the deeper hydrogeologic domain. For this purpose, a MATLAB package (Modalstrata) has been developed to improve the correlation of the stratigraphic succession for each selected homogeneous sub-area and applied to obtain a new, upgraded hydrostratigraphic model. The horizontal to vertical spectral ratio passive seismic surveys have confirmed the lateral correlations among the sample areas at least for the two main aquifer horizons. Analysis and comparisons of several previous studies performed on the data related to the only drilling continuous coring 951 m deep in the Tronchetto Island (Venice), have allowed a satisfactory validation of the proposed hydrogeological model.

On the seismic noise wavefield in a weakly dissipative layered Earth

SUMMARY Proceeding on the assumption that the seismic noise wavefield mainly consists of surface waves generated by a random distribution of independent, point-like and harmonic sources, we modelled a set of relationships that allows us to interpret empirical H/V and apparent dispersion curves in terms of the dynamic properties of a viscoelastic layered Earth. This formalization can be used to determine the effect of material damping on the expected noise wavefield in cases where the sources are relatively distant from the receivers and where the frequencies taken into account are higher than the fundamental resonance frequency of the local subsoil. Numerical experiments indicate that such effects are significant on the H/V ratio curve, whereas the apparent dispersion curve appears to be less strongly influenced by damping. This finding opens new perspectives for the use of noise measurements to infer the in situ anelastic properties of subsoil from passive seismic measurements made at the surface.