Earthquake location in tectonic structures of the Alpine Chain: the case of the Constance Lake (Central Europe) seismic sequence

Acta Geophysica ◽

10.1007/s11600-021-00594-6 ◽

2021 ◽

Author(s):

Francesca D’Ajello Caracciolo ◽

Rodolfo Console

Keyword(s):

Central Europe ◽

Velocity Model ◽

Moho Depth ◽

Seismic Sequence ◽

Tectonic Structures ◽

Study Region ◽

Waveform Data ◽

Seismic Stations ◽

Velocity Models ◽

Master Event

AbstractA set of four magnitude Ml ≥ 3.0 earthquakes including the magnitude Ml = 3.7 mainshock of the seismic sequence hitting the Lake Constance, Southern Germany, area in July–August 2019 was studied by means of bulletin and waveform data collected from 86 seismic stations of the Central Europe-Alpine region. The first single-event locations obtained using a uniform 1-D velocity model, and both fixed and free depths, showed residuals of the order of up ± 2.0 s, systematically affecting stations located in different areas of the study region. Namely, German stations to the northeast of the epicenters and French stations to the west exhibit negative residuals, while Italian stations located to the southeast are characterized by similarly large positive residuals. As a consequence, the epicentral coordinates were affected by a significant bias of the order of 4–5 km to the NNE. The locations were repeated applying a method that uses different velocity models for three groups of stations situated in different geological environments, obtaining more accurate locations. Moreover, the application of two methods of relative locations and joint hypocentral determination, without improving the absolute location of the master event, has shown that the sources of the four considered events are separated by distances of the order of one km both in horizontal coordinates and in depths. A particular attention has been paid to the geographical positions of the seismic stations used in the locations and their relationship with the known crustal features, such as the Moho depth and velocity anomalies in the studied region. Significant correlations between the observed travel time residuals and the crustal structure were obtained.

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Assessing uncertainties in velocity models and images with a fast nonlinear uncertainty quantification method

Geophysics ◽

10.1190/geo2017-0321.1 ◽

2018 ◽

Vol 83 (2) ◽

pp. R63-R75 ◽

Cited By ~ 15

Author(s):

Gregory Ely ◽

Alison Malcolm ◽

Oleg V. Poliannikov

Keyword(s):

Uncertainty Quantification ◽

Seismic Imaging ◽

Low Frequency ◽

Expansion Method ◽

Velocity Model ◽

Image Features ◽

Visible Image ◽

Waveform Data ◽

Velocity Models ◽

Seismic Reflections

Seismic imaging is conventionally performed using noisy data and a presumably inexact velocity model. Uncertainties in the input parameters propagate directly into the final image and therefore into any quantity of interest, or qualitative interpretation, obtained from the image. We considered the problem of uncertainty quantification in velocity building and seismic imaging using Bayesian inference. Using a reduced velocity model, a fast field expansion method for simulating recorded wavefields, and the adaptive Metropolis-Hastings algorithm, we efficiently quantify velocity model uncertainty by generating multiple models consistent with low-frequency full-waveform data. A second application of Bayesian inversion to any seismic reflections present in the recorded data reconstructs the corresponding structures’ position along with its associated uncertainty. Our analysis complements rather than replaces traditional imaging because it allows us to assess the reliability of visible image features and to take that into account in subsequent interpretations.

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A new 3D velocity model of Central Apennines: insights from 2D/3D geological modelling and earthquake relocation.

10.5194/egusphere-egu21-7118 ◽

2021 ◽

Author(s):

Andrea D'Ambrosio ◽

Eugenio Carminati ◽

Carlo Doglioni ◽

Lorenzo Lipparini ◽

Mario Anselmi ◽

...

Keyword(s):

Seismic Hazard ◽

Cross Sections ◽

3D Model ◽

Velocity Model ◽

Earthquake Relocation ◽

Central Apennines ◽

Seismic Stations ◽

Velocity Models ◽

3D Velocity Model ◽

Seismogenic Faults

The Central Apennines fold-and-thrust belt (Central Italy) is characterized by the presence of several active faults, potentially capable of generating damaging earthquakes. To support seismic hazard studies over the area, a new 3D velocity model was built, integrating a wide range of surface and subsurface data.The tectonic framework of the area (from Sulmona plain to Maiella Mt), is still debated in literature, also due to the lack of both an adequate geophysical data set and a reliable velocity model at the crustal scale.In addition, the low number of seismic stations available for the acquisition of Vp/Vs arrival times, and the very low seismicity detected in the study area (the Sulmona and Caramanico Apennine valleys are considered as &#8220;seismic gaps&#8221;), lead to a difficult interpretation of the subsurface tectonic structures.3D velocity modelling could well represent an important tool to support these deep crustal reconstructions as well earthquake relocation studies and could enhance the definition of seismogenic faults deep geometries, hence supporting a better risk assessment over the area of these potential locked faults.Using the knowledge developed within the oil&gas industry as well in gas/CO2 storage projects for the construction of 3D velocity models, extensively used to obtain subsurface imaging and define the geometry of the reservoirs and traps in the depth domain, a similar methodological approach was implemented over the study area.The subsurface dataset was partially inherited by the past hydrocarbon exploration activities (e.g. seismic lines, exploration wells and sonic logs) and by the literature (e.g. time/depth regional models). Tomographic sections and relocated earthquake hypocentres were also integrated form geophysical studies. Geological maps (1:50.000 & 1:100.000 scale) represent the surface dataset that we used to create the surface interpretation of the regional geology.As a first step, 18 2D balanced regional geological cross-sections, dip-oriented (W-E) across the Central Apennine, were built define the structural picture at regional scale. The cross-sections were built using MOVE (Petroleum Experts) and Petrel (Schlumberger) software. The following modelling step was the 3D model construction, in which the surface/subsurface data as well as all the geological sections were integrated in the final 3D structural and geological model.The main geological layers reconstructed in the 3D model were than populated using the appropriated interval velocity values, building the final 3D velocity model in which the lateral velocity variation due to the presence of different facies/geological domains were considered.As one of the results, we defined several 1D-velocity models coherent with the regional 3D velocity model, in which the key seismic stations and the earthquakes hypocentres dataset for the most potential seismogenic faults were included. 1D models were characterized by different degree of simplification, in order to test diverse approaches for the earthquake relocation. For this exercise, we used public dataset extracted by the analysis of microseismicity of the Sulmona basin.We believe that the proposed approach can represents an effective method for combining geological and geophysical data to improve the subsurface and seismogenic faults interpretation, contributing to the seismic hazard assessment.

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Detection of possible seismic station phase reversals using parametric data from seismological bulletins

10.5194/egusphere-egu21-3195 ◽

2021 ◽

Author(s):

Konstantinos Lentas

Keyword(s):

Goodness Of Fit ◽

Seismic Station ◽

Waveform Data ◽

Seismic Stations ◽

Velocity Models ◽

Parametric Data ◽

Source Mechanisms ◽

First Motion ◽

Earthquake Mechanism ◽

Using Data

A simple and fast technique to detect systematic changes in the performance of seismic stations by using parametric data is being presented. The methodology is based on a simple principal, notably, quantifying the goodness of fit of first motion manually picked polarities from seismological bulletins versus available earthquake mechanism solutions over time. The probability of the reporting polarity data fitting (and not fitting) source mechanisms is quantified by calculating the probability distribution of several Bernoulli trials over a randomly perturbed set of hypocentres and velocity models for each earthquake mechanism - station polarity combination. The method was applied to the registered seismic stations in the bulletin of the International Seismological Centre (ISC) after grouping each polarity pick by reporting agency, using data from the past two decades. The overall agreement of first motion polarities against source mechanisms is found to be good with a few cases of seismic stations showing indications of systematic phase reversals over certain time periods. Specifically, results were obtained for 50% of the registered stations at the ISC, and from these stations 70% show reliable operation during the operational time period under investigation, with only 3% showing the opposite, and 7% showing evidence of systematic changes in the quality of the reported first motion polarities. The rest showed great variability over short periods of time, which does not allow one to draw any conclusions. Comparing waveform data with the associated reported polarities revealed a mixture of cases of either questionable picking or true station phase reversals.

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Relocation of earthquakes in the southern and eastern Alps (Austria, Italy) recorded by the dense, temporary SWATH-D network using a Markov chain Monte Carlo inversion

Solid Earth ◽

10.5194/se-12-1087-2021 ◽

2021 ◽

Vol 12 (5) ◽

pp. 1087-1109

Author(s):

Azam Jozi Najafabadi ◽

Christian Haberland ◽

Trond Ryberg ◽

Vincent F. Verwater ◽

Eline Le Breton ◽

...

Keyword(s):

Monte Carlo ◽

Markov Chain ◽

Markov Chain Monte Carlo ◽

Velocity Model ◽

Eastern Alps ◽

Inversion Method ◽

Parameter Uncertainties ◽

Waveform Data ◽

Velocity Models ◽

Austroalpine Nappes

Abstract. In this study, we analyzed a large seismological dataset from temporary and permanent networks in the southern and eastern Alps to establish high-precision hypocenters and 1-D VP and VP/VS models. The waveform data of a subset of local earthquakes with magnitudes in the range of 1–4.2 ML were recorded by the dense, temporary SWATH-D network and selected stations of the AlpArray network between September 2017 and the end of 2018. The first arrival times of P and S waves of earthquakes are determined by a semi-automatic procedure. We applied a Markov chain Monte Carlo inversion method to simultaneously calculate robust hypocenters, a 1-D velocity model, and station corrections without prior assumptions, such as initial velocity models or earthquake locations. A further advantage of this method is the derivation of the model parameter uncertainties and noise levels of the data. The precision estimates of the localization procedure is checked by inverting a synthetic travel time dataset from a complex 3-D velocity model and by using the real stations and earthquakes geometry. The location accuracy is further investigated by a quarry blast test. The average uncertainties of the locations of the earthquakes are below 500 m in their epicenter and ∼ 1.7 km in depth. The earthquake distribution reveals seismicity in the upper crust (0–20 km), which is characterized by pronounced clusters along the Alpine frontal thrust, e.g., the Friuli-Venetia (FV) region, the Giudicarie–Lessini (GL) and Schio-Vicenza domains, the Austroalpine nappes, and the Inntal area. Some seismicity also occurs along the Periadriatic Fault. The general pattern of seismicity reflects head-on convergence of the Adriatic indenter with the Alpine orogenic crust. The seismicity in the FV and GL regions is deeper than the modeled frontal thrusts, which we interpret as indication for southward propagation of the southern Alpine deformation front (blind thrusts).

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Detailed Investigation of Seismic Anisotropy in the Upper Mantle of the Northern Aegean Region

10.5194/egusphere-egu2020-1088 ◽

2020 ◽

Author(s):

Ceyhun Erman ◽

Seda Yolsal-Çevikbilen ◽

Tuna Eken ◽

Tuncay Taymaz

Keyword(s):

Upper Mantle ◽

Seismic Anisotropy ◽

Broad Band ◽

Mantle Flow ◽

Data Set ◽

Study Region ◽

Waveform Data ◽

Seismic Stations ◽

Aegean Region ◽

Fast Polarization

Seismic anisotropy studies can provide important constraints on geodynamic processes and deformation styles in the upper mantle of tectonically active regions. Seismic anisotropy parameters (e.g. delay time and fast polarization direction) can give hints at the past and recent deformations and can be most conventionally obtained through core-mantle refracted SKS phase splitting measurements. In order to explore the complexity of anisotropic structures in the upper mantle of a large part of the Aegean region, in this study, we estimate splitting parameters beneath 25 broad-band seismic stations located at NW Anatolia, North Aegean Sea and Greece mainland. To achieve this we employ both transverse energy minimization and eigenvalue methods. Waveform data of selected earthquakes (with Mw &#8805; 5.5; 2008-2018 and with epicentral distances between 85&#176;&#8211;120&#176;) were retrieved from Earthquake Data Center System of Turkey (AFAD; http://tdvm.afad.gov.tr/) and European Integrated Data Archive (EIDA; http://orfeus-eu.org/webdc3/). A quite large data set, the majority of which have not been studied before, were evaluated in order to estimate reliable non-null and null results. In general, station-averaged splitting parameters mainly exhibit the NE-SW directed fast polarization directions throughout the study area. These directions can be explained by the lattice-preferred orientation of olivine minerals in the upper mantle induced by the mantle flow related to the roll-back process of the Hellenic slab. We further observe that station-averaged splitting time delays are prone to decrease from north to south of the Aegean region probably changing geometry of mantle wedge with a strong effect on&#160; the nature of mantle flow along this direction. The uniform distribution of splitting parameters as a function of back-azimuths of earthquakes refers to a single-layer horizontal anisotropy for the most part of the study area. However, back azimuthal variations of splitting parameters beneath most of northerly located seismic stations (e.g., GELI, SMTH etc.) imply the presence of a double-layer anisotropy. To evaluate this, we performed various synthetic tests especially beneath the northern part of study region. Yet, it still remains controversial issue due to the large azimuthal gap and thus requires further modelling which may involve the use of joint data sets.

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Frequency and spatial sampling strategies for crosshole seismic waveform spectral inversion experiments

Geophysics ◽

10.1190/1.3157252 ◽

2009 ◽

Vol 74 (6) ◽

pp. WCC79-WCC89 ◽

Cited By ~ 26

Author(s):

Hansruedi Maurer ◽

Stewart Greenhalgh ◽

Sabine Latzel

Keyword(s):

Information Content ◽

Seismic Data ◽

Velocity Model ◽

Similar Amount ◽

Data Sets ◽

Data Set ◽

Waveform Data ◽

Velocity Models ◽

Seismic Waveform ◽

Iterative Inversion

Analyses of synthetic frequency-domain acoustic waveform data provide new insights into the design and imaging capability of crosshole surveys. The full complex Fourier spectral data offer significantly more information than other data representations such as the amplitude, phase, or Hartley spectrum. Extensive eigenvalue analyses are used for further inspection of the information content offered by the seismic data. The goodness of different experimental configurations is investigated by varying the choice of (1) the frequencies, (2) the source and receiver spacings along the boreholes, and (3) the borehole separation. With only a few carefully chosen frequencies, a similar amount of information can be extracted from the seismic data as can be extracted with a much larger suite of equally spaced frequencies. Optimized data sets should include at least one very low frequencycomponent. The remaining frequencies should be chosen fromthe upper end of the spectrum available. This strategy proved to be applicable to a simple homogeneous and a very complex velocity model. Further tests are required, but it appears on the available evidence to be model independent. Source and receiver spacings also have an effect on the goodness of an experimental setup, but there are only minor benefits to denser sampling when the increment is much smaller than the shortest wavelength included in a data set. If the borehole separation becomes unfavorably large, the information content of the data is degraded, even when many frequencies and small source and receiver spacings are considered. The findings are based on eigenvalue analyses using the true velocity models. Because under realistic conditions the true model is not known, it is shown that the optimized data sets are sufficiently robust to allow the iterative inversion schemes to converge to the global minimum. This is demonstrated by means of tomographic inversions of several optimized data sets.

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Implications of 3D Seismic Raytracing on Focal Mechanism Determination

Bulletin of the Seismological Society of America ◽

10.1785/0120190184 ◽

2019 ◽

Vol 109 (6) ◽

pp. 2746-2754

Author(s):

Katharina Newrkla ◽

Hasbi Ash Shiddiqi ◽

Annie Elisabeth Jerkins ◽

Henk Keers ◽

Lars Ottemöller

Keyword(s):

Focal Mechanism ◽

Historical Earthquakes ◽

Velocity Model ◽

Waveform Data ◽

Focal Mechanism Solutions ◽

Velocity Models ◽

Maximum Value ◽

3D Velocity Model ◽

First Motion

Abstract The purpose of this study is to investigate apparent first‐motion polarities mismatch at teleseismic distances in the determination of focal mechanism. We implement and compare four seismic raytracing algorithms to compute ray paths and travel times in 1D and 3D velocity models. We use the raytracing algorithms to calculate the takeoff angles from the hypocenter of the 24 August 2016 Mw 6.8 Chauk earthquake (depth 90 km) in central Myanmar to the stations BFO, GRFO, KONO, and ESK in Europe using a 3D velocity model of the upper mantle below Asia. The differences in the azimuthal angles calculated in the 1D and 3D velocity models are considerable and have a maximum value of 19.6°. Using the takeoff angles for the 3D velocity model, we are able to resolve an apparent polarity mismatch where these stations move from the dilatational to the compressional quadrant. The polarities of synthetic waveforms change accordingly when we take the takeoff angles corresponding to the 3D model into account. This method has the potential to improve the focal mechanism solutions, especially for historical earthquakes where limited waveform data are available.

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Micro-seismicity, seismic-wave velocity model and earthquake clustering in the Akarnanian region (western Greece)

10.5194/egusphere-egu21-7672 ◽

2021 ◽

Author(s):

Valentine Lefils ◽

Alexis Rigo ◽

Efthimios Sokos

Keyword(s):

Deformation Mode ◽

Velocity Model ◽

Local Velocity ◽

Low Velocity ◽

Tectonic Structures ◽

Seismic Wave Velocity ◽

Velocity Models ◽

Gulf Of Corinth ◽

Western Greece ◽

Seismological Network

Characterized for the first time in 2013, the Island Akarnanian Block (IAB) is a micro-plate located in the western Greece. This micro-plate accommodates the deformation in between larger scale tectonic structures as the Gulf of Corinth (South-East), the Hellenic subduction (South) and the Apulian Collison (West).We started a micro-seismic survey (MADAM) at the end of 2015 with a dense seismological network over the area, between the Gulf of Patras and the Gulf of Amvrakikos. In order to obtain precise locations of the recorded events, we better constrained the local velocity model. In fact, several velocity models (local or regional) have been proposed for this area. However, the velocity model generally used by the scientific community remains the Hasslinger 98 velocity model. This model, nevertheless, raises some questions about its physical meaning, mainly due to a low velocity layer between 4 and 7 km-depth. Thanks to our seismological network and permanent networks of the Corinth Rift Laboratory and the Hellenic Unified Seismic Network, we collected and analysed a huge quantity of data acquired between October 2015 and December 2017. Those analyses of more than 10,000 events allowed us to develop a new and robust local velocity model, which is consistent with the seismic data and the geophysical observations.The observed seismic activity is characterized by the presence of numerous clusters. The clusters are analysed in detail by relative relocations in order to appraise their physical processes and their possible implications in the fault activity to finally have a better understanding of the deformation mode(s) of the IAB micro-plate.

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VELOCITY MODEL OF CRUST OF AZERBAIDJAN ON DATA OF DIGITAL SEISMIC STATIONS

Геология и геофизика Юга России ◽

10.23671/vnc.2012.1.55585 ◽

2012 ◽

Author(s):

Г.Д. Етирмишли ◽

С.Э. Казымова

Keyword(s):

Velocity Structure ◽

Three Dimensional ◽

Velocity Model ◽

Design Calculation ◽

Travel Times ◽

Seismic Stations ◽

One Dimensional ◽

S Waves ◽

Velocity Models ◽

Seismological Data

При изучении скоростной структуры земной коры Азербайджана по сейсмологическим данным ис- пользовались в основном два подхода. Первый состоит в уточнении модели среды на основании наблюда- емых отклонений времен пробега волн от землетрясений относительно стандартного годографа. Второй основан на использовании разности времен пробега от источников до станции для групп близко располо- женных событий. Одномерные скоростные модели Р и S-волн были построены на основе одномерных моделей, пред- ложенных в работе Гасанова А.Г. Построение модели, расчет станционных поправок и перелокация со- бытий производились в программе Velest. Исследуемый объем до глубины 60 км был разбит на мелкие слои толщиной 2 км в интервале глубин 010 км и толщиной 510 км в интервале глубин 1060 км. В ходе исследования рассматривались сейсмологические данные о параметрах локальных землетрясений и вре- менах прихода P и S-волн зарегистрированных сетью телеметрических станций за период 20042011 гг. Анализировались данные 28-ми сейсмических станций Азербайджана, охватывающие всю исследуемую территорию. Для расчета трехмерного скоростного поля использовалась программа TomotetraFD. В этой програм- ме реализован классический сейсмотомографический метод для случая, когда источники и приемники находятся внутри исследуемого региона. Two approaches were used for investigation of crust velocity structure of Azerbaijan on the basis of seismological data. The first one consists in medium model adjustment on the basis of observed deviation of travel times of waves from earthquakes relative to standard hodograph. The second is based on difference in travel times from source to station for a group of close located stations. One dimensional velocity models of P- and S-waves were constructed on the basis of one dimensional models proposed by A.G.Gasanov. Model design, calculation of stations corrections and relocationing of events 74 Геология и геофизика Юга России, 1, 2012 were performed in Velest program. Investigating volume to depth of 60 km was divided in small layers of 2 km thickness in 0-10 km interval and 5-10 km in 10-60 km interval. Seismological data about parameters of local earthquakes registered by network of telemetric stations in 2004-2011 and arrival times of P- and S-waves were used. Data of 28 seismic stations of Azerbaijan covering all the investigating territory were analyzed. Three dimensional velocity field was calculated by means of TomotetraFD program. Classical seismotomographical method for the case when sources and receivers are located within investigating region is realized in the program.

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The crustal structure of the southern Nain and Makkovik provinces of Labrador derived from refraction seismic data

Canadian Journal of Earth Sciences ◽

10.1139/e08-007 ◽

2008 ◽

Vol 45 (4) ◽

pp. 465-481 ◽

Cited By ~ 4

Author(s):

Thomas Funck ◽

Annette K. Hansen ◽

Ian D. Reid ◽

Keith E. Louden

Keyword(s):

Crustal Structure ◽

Velocity Model ◽

Seismic Profile ◽

P Wave ◽

Moho Depth ◽

S Wave ◽

Velocity Models ◽

Refraction Seismic ◽

Forward And Inverse Modeling ◽

Lower Crustal

Data from a refraction seismic profile parallel to the coast of Labrador (Canada) were used to determine the crustal structure across the boundary of the Nain and Makkovik provinces, and to look for evidence for an offshore continuation of the Mesoproterozoic Nain Plutonic Suite (NPS). Seven seismometers recorded airgun shots along the 283 km long line. P- and S-wave velocity models were developed from forward and inverse modeling of travel times. The velocity model distinguishes three distinct zones. In the Saglek block of the Nain Province, the crust is divided into three layers with P-wave velocities between 5.8 and 6.9 km/s. Farther to the south, upper crustal velocities increase to 6.3–6.5 km/s and the Poisson’s ratio increases from 0.24 to 0.27. This zone correlates with a gravity low that is interpreted to outline the offshore continuation of the NPS. The upper crustal velocities are intermediate between anorthositic and granitoid rock samples collected from the NPS. A lower crustal reflector is limited to the area underneath the NPS and may be related to dioritic magmas. Mid-crustal and lower crustal velocities do not vary along the line and no underplating was detected. Within the Makkovik Province, upper crustal velocities of 5.9–6.2 km/s may indicate a dioritic composition similar to the Island Harbour Bay plutonic suite. Moho depth varies between 28 and 36 km with the maximum beneath the NPS. The variations could not be linked to effects of the Makkovikian orogeny but are thought to relate to Mesozoic rifting in Labrador Sea.

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