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Raw records at two stations are shown in comparison with the filtered fundamental modes (a). Fundamental modes are drawn for the period range 12-40 s. The peak and trough technique sketch shows a mutual time shift of the corresponding filtered records. Amplitude spectra for both stations and both raw records (b) and fundamental modes (c) are shown. The instrumental transfer function is applied both in the time and frequency domain.
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We propose a new quantitative determination of shear wave velocities for distinct geological units in the Bohemian Massif,
Czech Republic (Central Europe). The phase velocities of fundamental Love wave modes are measured along two long profiles
(~200km) crossing three major geological units and one rift-like structure of the studied region. We have...
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... are set so that the taper smoothes two periods around one period which is kept unchanged. with the original record in Fig. 3a. The traditional peak and trough technique of manual estimation of phase velocity is demonstrated in this figure. The difference between the spectra of raw records and filtered fundamental modes is shown in Figs 3b and 3c. The filtered fundamental modes display similar waveforms in the time domain and similar shapes of spectra in the ...
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... for example, by Nafe and Brune (1960), McEvilly (1964), Wielandt et al. (1987). We use the correlation of filtered and truncated quasi-monochromatic components measured at two stations. Fig. 4 shows the coincidence of the harmonic components of stations HAJ and NEC shifted in time by 17 s. This rough time shift was introduced according to the Fig. 3a. In Fig. 4, we see that the time shift is set correctly in the period range around 19-20 s in this example, but for other periods, the waveforms are not so well correlated. We used the L 1 - norm to estimate the similarity of two signals while mutually shifting the signals sample by sample. We thus directly find the time difference for ...
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A number of recent studies have analyzed seismic rotational data using a relationship between transverse acceleration and rotation rate derived for a homogeneous full space. In this study we explore this relationship further theoretically by presenting a full ray theory (FRT) method to simulate rotational motions of fundamental mode seismic surface...
Citations
... Using the modeling approach by Nolet and Dahlen (2000), an array measurement of surface wave phase velocities based on the two-station method (Kolínský et al. 2011;Legendre et al. 2014) and array beamforming technique (Kolínský et al. 2014) can be computed. The predicted wavefield of the surface-wave fundamental mode Rayleigh waves over a selected region can be computed (Kolínský et al. 2019). ...
Data quality is of utmost importance in assessing seismic hazards and risk mitigation related to geohazards. Erroneous data incorporation may lead to inaccurate observations and judgments. Lack of data or clipped data can be dealt with easily, but errors in the data (e.g., timing, amplitudes) or in the metadata (e.g. location, gain) can induce some strong bias in the estimation of geohazards. As a result, strict and standard quality controls are required to guarantee the accuracy of the assessments. This chapter will discuss some of the common issues with seismological data and offer tips on identifying inaccuracies. Despite recent efforts by the seismological community, there is no uniform framework to identify the errors in seismological data nor to perform some established quality controls. Therefore, we will examine the current state of the art and best practices in seismological quality controls. Some recommendations for new implementations, including some cutting-edge technologies like “Dynamic Time Warping” will be suggested. Missing data (i.e., gaps) are permanent, but all erroneous data do not need to be discarded. In some cases, identifying the problem in the data or metadata allows for reprocessing. The problems with data availability will be examined first, then the challenges with data quality. Finally, a discussion on the metadata errors will be provided.KeywordsData qualityData metricsSeismic network performanceSeismologySeismic hazard
... The region has become the subject of many studies , and many references found in that review). Since the 1990s, many seismic structural measurements of a local or regional extent have been performed in the region (Novotný et al., 2013), namely the deep seismic sounding (Novotný, 1997), vertical incidence reflection (Tomek et al., 1997), surface wave dispersion (Kolínský & Brokešová, 2007;Kolínský et al., 2011), or the receiver function method (Wilde-Piórko et al., 2005;Heuer et al., 2006). The extended refraction and wide-angle reflection measurements GRANU'95 (Enderle et al., 1998), CELEBRATION 2000(Hrubcová et al., 2005, and SUDETES 2003 (Grad et al., 2003) enabled an investigation of the crust of the West Bohemia/Vogtland region on the regional scale up to Moho depths. ...
The intraplate West Bohemia region is characterized by relatively frequent earthquake swarms mostly concentrated in the vicinity of the Nový Kostel village. Records of selected microearthquakes of the 2008 seismic swarm from a small circular area around Nový Kostel with a radius of 11 km are processed with focus on availability of precise onset readings from all the selected events at all the selected stations. These data were used in the joint hypocenter-velocity inversion, employing the so-called isometric method which is especially efficient for this task. The results are two new one-dimensional velocity models, the constrained (smoother) and the unconstrained one, of the upper crust down to the depth of 11 km, and absolute locations of the selected earthquakes in the new constrained model. The foci delineate two segments of a steeply dipping fault zone. Time residuals at each of the stations display a remarkable azimuthal dependence, for both P and S waves, caused by anisotropy. No systematic dependence on epicentral distance was found even for stations outside the target area, which means that the new 1D models seem to be reasonable approximations of the real structure in the whole, much larger, West Bohemia region. No time dependence indicating possible changes of \(v_P\), \(v_S\) and their ratio during the swarm was observed. A set of P- and S-wave station corrections that should be used to correct onset times in order to reach precise absolute locations was derived as an integral part of the new models.
... These dispersion curves are averaged and then the representative dispersion curve is inverted to obtain a 1D S-wave velocity profile representing the monitoring network. We apply the methodology for the surface wave inversion developed and tested by Kolínský et al. (2011) and recently used by Belinić et al. (2021) with layer boundaries derived from the P-wave model. This allows us to constrain S-wave velocities in geological layers and compare resulting Vp/Vs ratio with known geology. ...
... To reconstruct the S-wave velocity profile, we invert the Rayleigh wave group velocity dispersion using the method developed and tested by Kolínský et al. (2011). The inversion starts with an initial velocity profile which is randomly modified in each iteration. ...
... By analyzing teleseismic records with the receiver function technique (e.g., the receiver functions at stations MOX, WET, BRG, and NKC shown in Figure 1), Wilde-Piórko et al. (2005) revealed the existence of an S-wave LVZ in the middle crust (depth range of 10-15 km) of the northwestern Bohemian Massif. With the help of Love wave phase velocity dispersion curves, Kolínský et al. (2011) discovered an S-wave LVZ in the middle and lower crust beneath the TB zone and a gradually increasing S-wave velocity structure in the crust of the ST zone. By applying ambient seismic noise interferometric surface wave tomography (ASNT) to the recordings of broadband seismic stations, Růžek et al. (2016) inverted group and phase dispersion curves to obtain crustal velocity models for the Bohemian Massif that monotonically increase with depth; they concluded that the differences among different tectonic units are small and that the most homogeneous part among them generally being the middle crust. ...
... Nevertheless, the crustal models derived from previous studies for the Bohemian Massif present different, even contradictory results regarding the existence of the LVZ in the middle crust (e.g., Enderle et al., 1998;Wilde-Piórko et al., 2005;Grad et al., 2008;Kolínský et al., 2011;Růžek et al., 2016;Kästle et al., 2018;Lu et al., 2018;Kvapil et al., 2021). To address this inconsistency, in this study, we apply our newly developed multimodal ambient noise dispersion curve tomography method, denoted the frequency-Bessel transform (F-J) method , to investigate the crustal structure beneath the study area by using available ambient seismic noise datasets. ...
... The models obtained via the joint inversion of multimodal dispersion curves based on the F-J method reveal obvious lowvelocity characteristics in the crust and uppermost mantle beneath the study area. Other studies similarly provided evidence for the existence of an LVZ in this region (e.g., Wilde-Piórko et al., 2005;Kolínský et al., 2011;Kvapil et al., 2021). Based on our inversion results, we construct a simple S-wave velocity profile of the crust and uppermost mantle beneath the western side of the study area ( Figure 14B). ...
The northwestern Bohemian Massif and adjacent areas are a tectonically active region associated with complex geodynamic activities, that manifest as Quaternary volcanism, earthquake swarms in the upper and middle crust, degassing of CO2, and crustal fluid migration. The intricate tectonic evolution and activities of this region reflect the complexity of the crustal structure therein. However, the crustal models derived from previous studies in this area offer different, even contradictory information regarding the existence of a mid-crustal low-velocity zone (LVZ). In this study, we apply the frequency-Bessel transform (F-J) method to extract the fundamental-mode and up to five higher-mode Rayleigh wave dispersion curves from ambient seismic noise data recorded in the study area and perform multimodal ambient noise dispersion curves inversion. The addition of higher-mode dispersion curves enhances the vertical resolution of the velocity structure inversion results. Our models support the view that the general S-wave velocity level of the crust is high within the study area. We detect two S-wave LVZs beneath the study area that are distributed mainly in the middle crust rather than the lower crust, and these LVZs are separated by a high-velocity zone. Considering the results of previous studies in the area, we infer that these S-wave LVZs may be the consequence of crustal fluids, plastic deformation and even partial melting of the felsic middle crust at relatively high crustal temperatures. Furthermore, these S-wave LVZs could be responsible for the origin and foci depth distribution of earthquake swarms. S-wave low-velocity anomalies are also observed in the uppermost mantle beneath the study area. These S-wave models based on the joint inversion of multimodal dispersion curves can provide new references for understanding the tectonic activity and geodynamic evolution of the northwestern Bohemian Massif and adjacent areas.
... Most of the events are located in the Pacific seismic zone stretching from Chile to Japan, which results in reduced sampling from the south-east (Fig. 2a). Following Kolínský et al. (2011), a two-station method is used to determine phase velocity of the Rayleigh waves recorded on the Z and R components. We start by multiple filtering of each record. ...
... The number of layers was also tested to be sufficient for imaging the structural variations. Higher number of layers do not bring any qualitative change of the resulting models (Kolínský et al., 2011), it only smears the velocity gradients over more thinner layers. The ak135 model is used to set the density and vP/vS ratio. ...
... The resulting best model is then used as a starting model for the inversion at all grid nodes. While the inversion does not depend on the starting model, using a model close to the final one saves computational time (Kolínský et al., 2011(Kolínský et al., , 2014. Unrealistic velocity oscillations are avoided by constraining the velocity difference between neighboring layers. ...
The interaction between the Adriatic microplate (Adria) and Eurasia is the main driving factor in the central Mediterranean tectonics. Their interplay has shaped the geodynamics of the whole region and formed several mountain belts including Alps, Dinarides and Apennines. Among these, Dinarides are the least investigated and little is known about the underlying geodynamic processes. There are numerous open questions about the current state of interaction between Adria and Eurasia under the Dinaric domain. One of the most interesting is the nature of lithospheric underthrusting of Adriatic plate, e.g. length of the slab or varying slab disposition along the orogen. Previous investigations have found a low-velocity zone in the uppermost mantle under the northern-central Dinarides which was interpreted as a slab gap. Conversely, several newer studies have indicated the presence of the continuous slab under the Dinarides with no trace of the low velocity zone. Thus, to investigate the Dinaric mantle structure further, we use regional-to-teleseismic surface-wave records from 98 seismic stations in the wider Dinarides region to create a 3D shear-wave velocity model. More precisely, a two-station method is used to extract Rayleigh-wave phase velocity while tomography and 1D inversion of the phase velocity are employed to map the depth dependent shear-wave velocity. Resulting velocity model reveals a robust high-velocity anomaly present under the whole Dinarides, reaching the depths of 160 km in the north to more than 200 km under southern Dinarides. These results do not agree with 1 most of the previous investigations and show continuous underthrusting of the Adriatic lithosphere under Europe along the whole Dinaric region. The geometry of the down-going slab varies from the deeper slab in the north and south to the shallower underthrusting in the center. On-top of both north and south slabs there is a low-velocity wedge indicating lithospheric delamination which could explain the 200 km deep high-velocity body existing under the southern Dinarides.
... For the purposes of the current paper, we reprocessed the data mainly to obtain the measurements for more periods. To do so, we followed the procedure of phase velocity measurement described by Kolínský et al. (2011) and the array processing developed by Kolínský et al. (2014). The overall procedure is the same as used by Kolínský and Bokelmann (2019). ...
... Group velocity was estimated using the method described by Kolínský and Brokešová (2007) based on multiple filtering. This procedure is anyway part of the phase velocity calculation, as mentioned in Kolínský et al. (2011). Figure The comparison of the phase-wavefront propagation is shown in Figure C1, lower panel. ...
Stripe‐like patterns of surface wave arrival angle deviations have been observed by several seismological studies around the world, but this phenomenon has not been explained so far. Here we test the hypothesis that systematic arrival angle deviations observed at the AlpArray broadband seismic network in Europe are interference patterns caused by diffraction of surface waves at single small‐scaled velocity anomalies. We use the observed pattern of Rayleigh waves from two earthquakes under the Southern Atlantic Ocean, and we fit this pattern with theoretical arrival angles derived by a simple modeling approach describing the interaction of a seismic wavefield with small anomalies. A grid search inversion scheme is implemented, which indicates that the anomaly is located in Central Africa, with its head under Cameroon. Moreover, the inversion enables the characterization of the anomaly: The anomaly is inferred to be between 320 and 420 km wide, matching in length the 2,500 km long upper mantle low‐velocity region under the volcano‐capped swells of the Cameroon volcanic line. We show that this approach can be generally used for studying the upper mantle anomalies worldwide.
... The result of the inversion is independent of the starting model. However, by setting a proper starting model which is close to the resulting one, we can save the computational time (Kolínský et al., 2011). ...
... Such a group velocity dispersion curve is considered as reliable and filter-independent. For details of this approach see Kolínský (2004); Kolínský and Brokešová (2007) and Kolínský et al. (2011). ...
The study area of Western Carpathians belongs to one of the most seismically active regions in Slovakia, where the available velocity models are not precise enough for accurate location and determination of focal mechanism. To improve the uppermost part of the currently used models, seismic surface wave data from two blasts in the quarry Rohožník, recorded at the MKnet local seismic network, were analyzed. Group velocity dispersion curves of Rayleigh and Love waves were determined by the frequency-time analysis. A mean group velocity dispersion curve for Love and Rayleigh waves for the central part of the MKnet network was settled and consequently joint inversion, for the period range 0.9 – 2.7 s, was performed to obtain a 1-D velocity model using the isometric method. The 11-layered model extends to depth of 2.5 km and indicate increase of the velocities from the surface down to the depths of 0.9 km. Then, velocities slightly decrease. The minimum of the low-velocity zone is at the depth of 1.8 km after which the velocities moderately increase to the velocity of the halfspace with vP = 5.35 km/s and vS = 2.96 km/s.
... The assumption about great-circle-parallel propagation biases surface wave tomography (Lay & Kanamori 1985). For that reason many studies have corrected the two-station measurements of phase velocities for the true arrival angles (Baumont et al. 2002;Pedersen 2006;Kolínský et al. 2011;Foster et al. 2014b;Chen et al. 2018). Some (e.g. ...
... It takes advantage of two traditional approaches. The first one is the classical two-station method of measuring phase velocities between pairs of stations in the time domain as described by Kolínský et al. (2011). The second approach is array beamforming for determining the phase velocity and the true arrival angles of propagation for a given array. ...
... The measurement of time differences between quasimonochromatic signals is carried out according to the method described by Kolínský et al. (2011Kolínský et al. ( , 2014. Filtered and tapered quasi-monochromatic signals are shifted in time sample by sample and their correlation is computed for each time shift. ...
The dense AlpArray network allows studying seismic wave propagation with high spatial resolution. Here we introduce an array approach to measure arrival angles of teleseismic Rayleigh waves. The approach combines the advantages of phase correlation as in the two-station method with array beamforming to obtain the phase-velocity vector. 20 earthquakes from the first two years of the AlpArray project are selected, and spatial patterns of arrival-angle deviations across the AlpArray are shown in maps, depending on period and earthquake location. The cause of these intriguing spatial patterns is discussed. A simple wave-propagation modelling example using an isolated anomaly and a Gaussian beam solution suggests that much of the complexity can be explained as a result of wave interference after passing a structural anomaly along the wave paths. This indicates that arrival-angle information constitutes useful additional information on the Earth structure, beyond what is currently used in inversions.
... (M w > 6.0, ∆ ∈ [20 • −120 • ]). Following Kolínský et al. (2011), we used a two-sta on method for Rayleigh waves recorded on the component R. Two-sta on method assumes the plane-wave propaga on to determine the phase veloci es of surface waves. We use mul ple filtering as a method of frequency-me analysis to inden fy and taper out the fundamental mode. ...
... Mean dispersion curves for selected staon pairs were inverted for the shear-wave (and P-wave) velocity structure (Kolínský et al., 2011). For the inversion, we used the Isometric method. ...
The basic outline of the Dinarides formation evolves around the interaction between Adria microplate and European mainland due to the north-east movement of Adria. This interaction included many complex tectonic processes such as subduction, collision and extension. The Dinaric mountain belt is one of the most underresearched parts of the Alpine-Mediterranean collision zone. So far, most of the regional seismic studies were focused on the upper-middle crust while the deeper structures remained poorly investigated and the regional geodynamics is still not fully understood.
In order to get more details about the regional tectonic history, we use seismic surface wave data and investigate uppermost mantle structures beneath the Dinarides. We analyzed more than 250 teleseismic earthquakes recorded at 74 stations and used a two-station method to get Rayleigh wave dispersion measurement on an inter-station path length larger than one wavelength. We measured surface wave phase velocities at discrete periods in the range from 20 s to 160 s and inverted these results to obtain shear-wave velocity model. Our
preliminary results show negative velocity anomaly under the North-West Dinarides and positive anomaly beneath the Pannonian basin and the Adriatic sea, clearly supporting results from previous studies and strengthening the premise of a slab gap existence in the North-West Dinarides.
... We analyzed 47 regional-to-teleseismic earthquakes recorded at 58 sta ons. Following Kolínský et al. (2011), we used a two-sta on method for Rayleigh waves with an intersta on path length larger that one wavelength. Two-sta on method assumes the plane-wave propaga on to determine the phase veloci es of surface waves. ...
The Dinarides are the orogeny located in the central Mediterranean collision zone that formed due to the interaction between Adria microplate and the European mainland. Along with the creation of the Dinarides, the north-east movement of Adria and its interaction with Europe induced the formation of several other mountain
chains, namely the Alps, Apennines and Carpathians. Furthermore, this interaction also triggered many complex tectonic processes such as eastward extrusion in the Eastern Alps and an opening of the Pannonian basin due to the subduction and slab rollback in the Carpathians. Considering all the aforementioned processes, in order to piece together a tectonic history of the Central Mediterranean, it is essential to fully explore each of these processes. In comparison with the surrounding areas, the Dinarides are relatively poorly explored and tectonic processes that led to their formation are not well understood.
Therefore, in order to bring some new insights, we provide a first detailed study of surface wave dispersion in the Dinarides. Using regional-to-teleseismic Rayleigh waves, we created 2-D phase-velocity models at discrete periods in the range from 20 s to 160 s. We used a two-station method with an inter-station path length larger that one wavelength. For a total of 58 seismic stations, we calculated the dispersion curves and cross-correlated them with an acceptable great-circle pair. Our preliminary results show negative velocity anomaly under the central area of Dinarides and positive anomaly beneath Pannonian basin and Adriatic sea, clearly supporting the results of the previous studies.
