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Pure and Applied Geophysics (PAGEOPH) is one of the leading journals in the field of geophysics. The first issue was published in 1939; thus, the journal is celebrating its 80th anniversary in 2018. The aim of this paper is to provide a complete lifetime overview of the academic structure of the journal using bibliometric indicators. This analysis includes key factors such as the most cited articles, leading authors, originating institutions and countries, publication and citation structures, and the most commonly used keywords. The bibliometric data used to conduct this analysis comes from the Scopus database. Additionally, the visualization of similarities (VOS)viewer software is used to create a graphic map of some of the bibliometric results. The graphical analysis uses co-citation, bibliographic coupling and co-occurrence of keywords. The results indicate that PAGEOPH is a leading journal in the areas in which it is indexed, with publications from a wide range of authors, institutions, and countries around the world. [ABSTRACT FROM AUTHOR]

Explains that this issue contains a selection of papers presented in "Geodynamics of the Western Part of the Eurasia-Africa Plate Boundary (Azores-Tunisia)" workshop on May 31 to June 2, 2001 in Cadiz, Spain. Model for the orogenic evolution of the central part of the region; Subduction-subduction-transform fault triple junction in the Betic-Rif orogenic belt; Tectonic deformations in the frontal part of the Rif cordillera and the Sais basin.

A preface for the Volume 163 issue of "Pure & Applied Geophysics" is presented.

The article reviews the book "Frontiers in Geofluids", edited by B. Yardley, C. Manning and G. Garven.

Twenty-two papers on tsunamis are included in the Pure and Applied Geophysics topical issue "Twenty five years of modern tsunami science following the 1992 Nicaragua and Flores Island tsunamis: Volume I," reporting on the frontiers of tsunami science and research. The first three papers overview significant tsunamis of 1992–2018 and discuss the problems of tsunami cataloguing. The main focus of the next four papers is on specific details of historical tsunami events and field surveys. First, three papers are related to thorough analyses of several historical events based on macroseismic, seismological, and tsunami observations, tide gauge data, and modelling results: the 1907 Sumatra "tsunami earthquake," the 1941 Andaman Islands earthquake, and five great tsunamis in the Pacific Ocean (1946, 1952, 1957, 1960 and 1964). The last paper of the section concerns results of the field survey of the 2017 Bodrum-Kos tsunami. The reconstruction of the tsunami sources is the main target of the four following papers, with four events examined in detail: the historical 1810 Baja California, 1992 Flores Island, 2012 Haida Gwaii and 2015 Chilean (Illapel) tsunamis. A set of three papers address problems associated with landslide-generated tsunamis in three different regions: a modelling of the 2017 landslide and tsunami at Karrat Fjord, Greenland; a probabilistic analysis of the hazard from the Indus Canyon in the NW Indian Ocean; and a study of the landslide-induced tsunami hazard along the US East Coast. The next section, including three papers, reports on comparisons between different types of tsunami models, on numerical modelling of tsunami waves in the Caspian Sea, and on the modelling of magnetic signals at Easter Island, following the 2010 and 2015 Chilean tsunamis. The last group of five papers discusses tsunami hazard assessment and warning for various regions of the world oceans, including Alaska, the eastern and western Mediterranean, Australia, the Northeast Atlantic and the entire Pacific Ocean; one specific aspect of these studies is the compilation and efficient application of observed data, in particular, from DARTs. [ABSTRACT FROM AUTHOR]

Twenty papers on the study of tsunamis and respective tsunamigenic earthquakes are included in Volume II of the PAGEOPH topical issue 'Tsunami Science: Ten Years after the 2004 Indian Ocean Tsunami'. The papers presented in this second of two special volumes of Pure and Applied Geophysics reflect the state of tsunami science during this time, including five papers devoted to new findings specifically in the Indian Ocean. Two papers compile results from global observations and eight papers cover Pacific Ocean studies, focusing mainly on the 2011 Tohoku earthquake and tsunami. Remaining papers in this volume describe studies in the Atlantic Ocean and Mediterranean Sea and tsunami source studies. Overall, the volume not only addresses the pivotal 2004 Indian Ocean and 2011 Tohoku tsunamis, but also examines the tsunami hazard posed to other critical coasts in the world. [ABSTRACT FROM AUTHOR]

The article focuses on the commemoration of the journal on its 75th year of existence. It mentions historical papers presented in earlier volumes written for its 50th and 60th anniversaries. It discusses the first of those histories which were written by then Editor-in-Chief for regular issues, Professor Emil Okal, in 1989. It cites one of the topical issues published in the 1970s in the areas of earthquake prediction, seismic gaps in subduction zones, and the ozone layer.

The direct problem in gravimetry is one of the few areas of applied geophysics where complete, general and fully valid solutions are available. The common issue in the gravimetric direct problem is that there are several different solutions for even simple shaped bodies available throughout the literature. While the direct problem is single-valued, the general solutions (if possible to find analytically) are desired. The aim of the present paper is to bring clarity into the "information noise" which occurs in the literature for the case of the spherical shell/layer. We collected several different solutions and proved their equality (as special cases of the general solution). The differences between these solutions are caused by the symbolism used, but mostly by the different area of validity of each formula. The formulae are discussed and scored on several criteria. The general solutions for the gravitational potential and attraction on the rotational axis of the spherical shell are presented, as well as the solution for the biaxial ellipsoidal layer for comparison. [ABSTRACT FROM AUTHOR]

The gravity and magnetic data sets over a geothermal source are investigated to explore the geological features and geothermal system manifestations. The raw gravity data sets are firstly corrected for drift, latitude and free-air effects to obtain free-air anomalies. A new approach is utilized for Bouguer and terrain corrections. The model space, which is the mass from the reference surface to the ground surface, is parameterized by a very accurate and advanced meshing algorithm (octree and quadtree). The gravity effect of the model space is computed via numerical forward modelling and is considered as the Bouguer and terrain corrections. These corrections are subtracted from the free-air anomalies, which yields the complete Bouguer anomaly. The computed Bouguer anomalies are de-trended and transferred to residual anomalies by methods including polynomial fitting and two-stage methods. The residual gravity anomalies are inverted to obtain the subsurface density distribution. The density contrasts are estimated by minimizing the data and model objective functions through an efficient algorithm. The probable source of the geothermal system and other new gravity anomalies are successfully detected and inverted contrary to the results in previously published papers. The residual magnetic anomaly is also inverted and the obtained geometrical and physical parameters of the source body including minimum depth, shape and susceptibility are very close to the previous results. The new detected gravity anomaly and the main magnetic anomaly in the overlapped area of gravity and magnetic grids are located at almost the same place with almost the same depths, which confirms their probable common source. We developed the open source package (http://docs.simpeg.xyz/content/tutorials/03-gravity), which is accessible through SimPEG (Simulation and Parameter Estimation in Geophysics), for inverting the gravity and magnetic data sets. [ABSTRACT FROM AUTHOR]

In this article the author reflects on comment by researchers L.B. Pedersen and M. Beiki on his article related to depth estimation of simple causative sources from gravity gradient tensor (GGT) invariants and vertical components. He states that from theoretical point of view he agrees with them that his equation is not valid as gradients of the gravity field along the y direction and subsequently the invariant are zero.

A response from the authors of the article "Probabilistic Tsunami Hazard in the Northeast Atlantic From Near- and Far-Field Tectonic Sources" that was published in the previous issue is presented.

The evolution laws of LURR (Loading-Unloading Response Ratio) before strong earthquakes, especially the peak point of LURR, are described in this paper. The results of four methods (experimental, numerical simulation, seismic data analysis and with damage mechanics analysis) lead to a consistent conclusion-the evolution laws of LURR before strong earthquakes are that, at the early stage of the seismic cycle, LURR will fluctuate around 1 and in the late stage, it rises swiftly and to its peak point. At some time after this peak point, a catastrophic event or events occur. These do not occur at the peak point, but lag behind. The lag time which is denoted by T depends on the magnitude M of the upcoming earthquake among other factors. In order to consider the influence of geophysical parameters in a specific region such as $$ \dot{\gamma }, $$ E and J, where $$ \dot{\gamma } $$ is the shear strain rate of tectonic loading in situ, E is the sum of radiated energy of all earthquake occurring in a specific region measured during a long time duration (110 years in this paper) divided by the area of the region and the time duration, and J is a parameter denoting the LURR anomaly area weighted with Y (the value of LURR) and represents the expanse and degree of the seismogenic zone. The dimensional analysis method has been used to reveal the relation between M, T and other parameters in situ for more reliable earthquake prediction. [ABSTRACT FROM AUTHOR]

Two large earthquakes occurred in the western part of China in 2008, one of them being the Yutian (35.6°N, 81.6°E) M7.3 earthquake that occurred on March 21 (BJT) and the other the Wenchuan (31.0°N, 103.4°E) M8.0 earthquake that occurred on May 12 (BJT). In this paper, the West Continental China (included in 20.0°-50.0°N, 70.0°-110.0°E region) was the study region for verifyong the predictability of the pattern informatics (PI) method using the receiver-operating characteristic curve (ROC) test and R score test. Different forecasting maps with different calculating parameters were obtained. The calculating parameters were the grid size Δ x, base time t, reference interval t to t, change interval t to t, and forecasting interval t to t. In this paper, the base time t fixed to June 1, 1971, the ending forecast time t fixed to June 1, 2008, and the forecasting interval t to t changed from 1 to 10 years, and the grid sizes were chosen as 1° × 1° and 2° × 2°, respectively. The results show that the PI method could forecast the Yutian M7.3 and Wenchuan M8.0 earthquakes only using suitable parameters. Comparing the forecast results of grid sizes 1° × 1° and 2° × 2°, the models with 2° × 2° grids were better. Comparing the forecast results with different forecasting windows from 1 to 10 years, the models with forecasting windows of 4-8 years were better using the ROC test, and the models with forecasting windows of 7-10 years were better using the R score test. The forecast efficiency of the model with a grid size of 2° × 2° and forecast window of 8 years was the best one using either the ROC test or the R score test. [ABSTRACT FROM AUTHOR]

The article reflects on various journals on geophysics. The journal "Pure and Applied Geophysics" has completed 70 years, one of the earliest journals dedicated to publishing research articles in geophysics. Mario Bossolasco, director of the Royal Institute of Geophysics and Geodesy, in Messina, Italy established a new journal, "Geofisica Pura e Applicata," which would cover all aspects of research in geophysics, both academic and applied.

A preface for the volume 174, 2007 issue of "Pure and Applied Geophysics" journal is presented.

Presents an introduction to the June 1, 2005 issue of the journal "Pure and Applied Geophysics."

This paper is the second of a set of two papers in which we study the inverse refraction problem. The first paper, “Types of Geophysical Nonuniqueness through Minimization,” studies and classifies the types of nonuniqueness that exist when solving inverse problems depending on the participation ofa prioriinformation required to obtain reliable solutions of inverse geophysical problems. In view of the classification developed, in this paper we study the type of nonuniqueness associated with the inverse refraction problem. An approach for obtaining a realistic solution to the inverse refraction problem is offered in a third paper that is in preparation.The nonuniqueness of the inverse refraction problem is examined by using a simple three-layer model. Like many other inverse geophysical problems, the inverse refraction problem does not have a unique solution. Conventionally, nonuniqueness is considered to be a result of insufficient data and/or error in the data, for any fixed number of model parameters. This study illustrates that even for overdetermined and error free data, nonlinear inverse refraction problems exhibit exact-data nonuniqueness, which further complicates the problem of nonuniqueness. By evaluating the nonuniqueness of the inverse refraction problem, this paper targets the improvement of refraction inversion algorithms, and as a result, the achievement of more realistic solutions. The nonuniqueness of the inverse refraction problem is examined initially by using a simple three-layer model. The observations and conclusions of the three-layer model nonuniqueness study are used to evaluate the nonuniqueness of more complicatedn-layer models and multi-parameter cell models such as in refraction tomography.For any fixed number of model parameters, the inverse refraction problem exhibits continuous ranges of exact-data nonuniqueness. Such an unfavorable type of nonuniqueness can be uniquely solved only by providing abundanta prioriinformation. Insufficienta prioriinformation during the inversion is the reason why refraction methods often may not produce desired results or even fail. This work also demonstrates that the application of the smoothing constraints, typical when solving ill-posed inverse problems, has a dual and contradictory role when applied to the ill-posed inverse problem of refraction travel times. This observation indicates that smoothing constraints may play such a two-fold role when applied to other inverse problems. Other factors that contribute to inverse-refraction-problem nonuniqueness are also considered, including indeterminacy, statistical data-error distribution, numerical error and instability, finite data, and model parameters. [ABSTRACT FROM AUTHOR]

In a set of two papers we study the inverse problem of refraction travel times. The purpose of this work is to use the study as a basis for development of more sophisticated methods for finding more reliable solutions to the inverse problem of refraction travel times, which is known to be nonunique. The first paper, “Types of Geophysical Nonuniqueness through Minimization,” emphasizes the existence of different forms of nonuniqueness in the realm of inverse geophysical problems. Each type of nonuniqueness requires a different type and amount ofa prioriinformation to acquire a reliable solution. Based on such coupling, a nonuniqueness classification is designed. Therefore, since most inverse geophysical problems are nonunique, each inverse problem must be studied to define what type of nonuniqueness it belongs to and thus determine what type ofa prioriinformation is necessary to find a realistic solution. The second paper, “Quantifying Refraction Nonuniqueness Using a Three-layer Model,” serves as an example of such an approach. However, its main purpose is to provide a better understanding of the inverse refraction problem by studying the type of nonuniqueness it possesses. An approach for obtaining a realistic solution to the inverse refraction problem is planned to be offered in a third paper that is in preparation.The main goal of this paper is to redefine the existing generalized notion of nonuniqueness anda prioriinformation by offering a classified, discriminate structure. Nonuniqueness is often encountered when trying to solve inverse problems. However, possible nonuniqueness diversity is typically neglected and nonuniqueness is regarded as a whole, as an unpleasant “black box” and is approached in the same manner by applying smoothing constraints, damping constraints with respect to the solution increment and, rarely, damping constraints with respect to some sparse reference information about the true parameters. In practice, when solving geophysical problems different types of nonuniqueness exist, and thus there are different ways to solve the problems. Nonuniqueness is usually regarded as due to data error, assuming the true geology is acceptably approximated by simple mathematical models. Compounding the nonlinear problems, geophysical applications routinely exhibit exact-data nonuniqueness even for models with very few parameters adding to the nonuniqueness due to data error. While nonuniqueness variations have been defined earlier, they have not been linked to specific use ofa prioriinformation necessary to resolve each case. Four types of nonuniqueness, typical for minimization problems are defined with the corresponding methods for inclusion ofa prioriinformation to find a realistic solution without resorting to a non-discriminative approach. The above-developed stand-alone classification is expected to be helpful when solving any geophysical inverse problems. [ABSTRACT FROM AUTHOR]

— Shallow landslides are often linked to high magnitude rainstorms. Research has attempted to establish threshold rainfall totals that trigger shallow landslides, based mainly on field evidence. Complications arise because not all regolith has the same hydrological behaviour, and research frequently fails to take this into account. This paper uses a combination of field and modelling approaches to explore the triggering rainfall thresholds for shallow failures in deforested hill country of New Zealand. It emphasises the role of variations in regolith hydrology, focussing on unsaturated and saturated zone responses. By using a modelling approach, detailed variations in pore pressure (positive and negative) responses are investigated, developing ideas initially derived from field evidence. This paper defines and develops earlier research that establishes values for maximum and minimum probability thresholds for shallow landslides, and provides a more generalised model that can be applied more widely. Hydrological mechanisms for shallow landslides are investigated in greater detail than previously possible using a Combined Hydrology And Stability Model (CHASM™). [ABSTRACT FROM AUTHOR]

Three-dimensional coordinate systems define the location of zero-dimensional points. Higher dimensional spatial objects such as lines and planes become apparent from sets of adjacent points. Any point defined in three-dimensional space within a sedimentary basin could be simultaneously located on the surface of a sand grain and a bedding plane in a kilometer-scale fold, and structure at any other scale. Therefore, like many other aspects of geology and geophysics, structural geology is multiscale which is why filtering, smoothing, scale bars and the like are prerequisites for any kind of geological mapping and outcrop imagery. It is argued here that the association of points with higher-dimensional objects that form the spatial building blocks of geology singles out length scale as a geometrical parameter that is fundamental to the definition of an object. Properties such as curvature, porosity, color and so on can only be attributed after location and scale are defined. It is proposed that length scale be treated as a fourth spatial dimension in geological and geophysical applications, on an equal footing to the three spatial coordinate dimensions. The utility of adopting a four spatial dimension approach in geoscience is that it forces length scale to be explicitly specified in descriptions where it is routinely omitted, for example, measurements of structural orientation where a scale parameter greatly simplifies later mapmaking and model building. Taken together with geological time, it is convenient to define geological and geophysical structure in five spacetime dimensions. [ABSTRACT FROM AUTHOR]

The reassessment of mineral occurrences is a common and economically rational technical procedure, because it involves studies directed to targets defined in previous studies in mineral exploration. The targets definition can be based on indications of mineralization on the surface or in the contrast of measurable physical properties using geophysics and intrinsic to certain types of deposits. This paper discusses the results by the combination of the use of geophysical methods, DC resistivity and induced polarization on detailed study of a copper mineral occurrence, from the adaptation of techniques of modeling of mineral deposits in mining. The indications of mineralization in the area consist of malachite, quartz and barite in veins, recognized in volcanic tufts structurally embedded in andesites and metaconglomerates. Nine parallel lines of electrical tomography in Schlumberger arrangement were performed, which resulted in 2-D inversion models, interpolated in models of blocks, maps and pseudo 3-D isosurface models in a mineral deposits modeling program. The results allowed the recognition of areas with high chargeability (2.5 mV/V) and high resistivity (800 Ω m), relating to areas with disseminated sulphide ores and silicification, according to recognized evidence around the area distribution in regional recognition. This is where the pseudo 3-D products enabled an estimate morphology of the deposit and clearly defined targets for sampling by drilling and quantification of results. The results allow the recommendation of this procedure in mineral exploration activities, supported by the quickness and possible global reduction of project costs, with real increase in the chances of incorporation of new deposits. This Reduces the costs for research development and minimizes the environmental impacts associated with mining as well as the application of these methods for environmental diagnosis. [ABSTRACT FROM AUTHOR]

The integrated interpretation of data from various technologies has the potential to obtain a more accurate estimate of subterranean earth properties. In this paper, we implement the joint interpretation of geological and geophysical data for mineral exploration in the northeastern region of Inner Mongolia, China. The joint application of several methodologies reduces the exploration risk. We first determined an approximate and large potential area for mineral exploration with geological data and magnetic data interpretation in Gaoerqi. Results from the two types of data analysis show that the ore deposit strikes roughly east in the northern part of the Gaoerqi mining area. Next, we employed the audio-magnetotelluric (AMT) method to study the subterranean electrical resistivity distribution and divide the earth into four layers. Inverted resistivity sections from the AMT data illustrate that the ore deposits are likely developed in the low-resistivity zone of the survey area from the land surface to 300-m depth. Finally, the high-resolution borehole-to-surface electrical resistivity tomography (ERT) method was employed for further investigation of the location and attitude of the potential ore deposits. Inverted resistivity sections from the ERT data show that two prospective areas for mineral exploration were observed in the west of the survey area and that the eastern portion of the survey area warrants further investigation. [ABSTRACT FROM AUTHOR]

Anomaly analysis is used for various geophysics applications such as determination of geophysical structure's location and border detections. Besides the classical geophysical techniques, artificial intelligence based image processing algorithms have been found attractive for geophysical anomaly analysis. Recently, cellular neural networks (CNN) have been applied to geophysical data and satisfactory results are reported. CNN provides fast and parallel computational capability for geophysical image processing applications due to its filtering structure. The behavior of CNN is defined by two template matrices that are adjusted by a properly supervised learning algorithm. After training stage for geophysical data, Bouguer anomaly maps can be processed and analyzed sequentially. In this paper, CNN learning and processing capability have been improved, combining Wavelet functions and backpropagation learning algorithms. The new architecture is denoted as Wavelet-Cellular Neural networks (Wave-CNN) and it is employed to analyze Bouguer anomaly maps which are important to extract useful information in geophysics. At first, Wave-CNN performance is tested on synthetic geophysical data, which are created by a computer environment. Then, Bouguer anomaly maps of the Dumluca iron ore field have been analyzed and results are reported in comparison to real drilling results. [ABSTRACT FROM AUTHOR]

In this paper we have developed a new method for measuring in situ soil permeability, which is based on the theory of radial gas advection through an isotropic porous medium. The method was tested in the laboratory and at several locations on the island of Vulcano (Aeolian Islands, Italy). It consists of a special device which generates a gas source at a depth of 50 cm and it permits measurement of the relative induced pressure in nearby soil at different depths. The characteristic error of the method was less than 10%. Furthermore, soil permeability measurements were carried out in the island of Vulcano during different periods of the year (between May 2000 and June 2001). A strong decrease in permeability in the upper layers of the soil during and after rainfall was noted, with very poor correlations between the spatial distributions of soil CO2 flux and shallow soil permeability. [ABSTRACT FROM AUTHOR]

Heavy tailed random variables (rvs) have proven to be an essential element in modeling a wide variety of natural and human-induced processes, and the sums of heavy tailed rvs represent a particularly important construction in such models. Oriented toward both geophysical and statistical audiences, this paper discusses the appearance of the Pareto law in seismology and addresses the problem of the statistical approximation for the sums of independent rvs with common Pareto distributionF(x)=1 -x-a for 1/2

- An algorithm recently developed by RUNDLEet al. (2002) to find regions of anomalous seismic activity associated with large earthquakes identified the location of anM w = 5.6 earthquake near Calexico, Mexico. In this paper we analyze the regional seismicity before this event, and a nearbyM w = 5.7 event, using time-to-failure algorithms developed by BOWMANet al. (1998) and BOWMAN and KING (2001a,b). The former finds the radius of a circular region surrounding the epicenter that optimizes the time-to-failure acceleration of seismic release. The latter optimizes acceleration based on the expected stress accumulation pattern for a dislocation source. Both methods found a period of accelerating seismicity in an optimal region, the size of which agrees with previously proposed scaling relations. This positive result suggests that the Rundle algorithm may provide a useful technique to identify regions of accelerating seismicity, which can then be analyzed using signal optimization time-to-failure techniques. [ABSTRACT FROM AUTHOR]

— The Indo-Burma (Myanmar) subduction boundary is highly oblique to the direction of relative velocity of the Indian tectonic plate with respect to the Eurasian plate. The area includes features of active subduction zones such as a Wadati-Benioff zone of earthquakes, a magmatic arc, thrust and fold belts. It also has features of oblique subduction such as: an arc-parallel strike-slip fault (Sagaing Fault) that takes up a large fraction of the northward component of motion and a buttress (the Mishmi block) that resists the motion of the fore-arc sliver. In this paper, I have examined the seismicity, slip vectors and principal axes of the focal mechanisms of the earthquakes to look for features of active subduction zones and for evidence of slip partitioning as observed in other subduction zones. The data set consists of Harvard CMT solutions of 89 earthquakes (1977–1999 with 4.8≦̸Mw≦̸7.2 and depths between 3–140 km). Most of these events are shallow and intermediate depth events occurring within the Indian plate subducting eastward beneath the Indo-Burman ranges. Some shallow events within the fore-arc region have arc-parallel Paxes, reflecting buttressing of the fore-arc sliver at its leading edge. Some of the shallowest events have nearly E-W oriented P axes which might account for recent folding and thrusting. Examination of earthquake slip vectors in this region shows that the slip vector azimuths of earthquakes in the region between 20°–26°N are rotated towards the trench normal, which is an indication of partial partitioning of the oblique convergence. It is seen that all aspects of seismicity, including the paucity of shallow underthrusting earthquakes and the orientation of P axes, are consistent with oblique convergence. The conclusions of this paper are consistent with recent geological studies and interpretations such as the coexistence of eastward subduction, volcanic activity and transcurrent movement through mid-Miocene to Quaternary period. [ABSTRACT FROM AUTHOR]

— The problem of the coseismic deformation induced by an earthquake on its own fault plane is investigated here. The analysis concentrates on the on-fault displacement field accompanying the occurrence of an earthquake in response to a prescribed uniform shear slip and it is carried out on the basis of the classical analytical model by Okada (1992) for a rectangular fault buried in an elastic homogeneous half-space delimited by a planar free surface. The analysis is subdivided into two separate papers: the first dealing with normal and the second with tangential on-fault displacements. In this first paper, concerning the study of the normal displacement component, the contributions of the source and of the correction introduced by the free surface are investigated separately and their dependence on the fault characteristics is thoroughly discussed. Particular attention is also devoted to the effects of the normal displacement on the fault surface geometry. It will be shown that the main effect is that of deforming the fault itself, with deformation consisting chiefly in a rotation of the plane and in a bending of the fault edges. The rotation angle is negligibly small (on the order of 1–10 μrad) for a single earthquake, although repeated seismic events occurring on the same fault might result in rotations of several degrees over geological time scales. [ABSTRACT FROM AUTHOR]

— This paper regards the on-fault displacement field generated by an earthquake on its own fault plane, with special attention to the tangential displacement vector. It is the continuation and the completion of a previous paper (Armigliato et al., 2003) concerning the analysis of the normal on-fault displacement component. It is here recognised that in addition to the discontinuous shear displacement, which is the main contribution to the seismic dislocation on the fault, there is a tangential displacement contribution that is continuous across the fault. The continuous tangential displacement is exclusively produced by the presence of the free earth's surface. The tangential displacement vector has non-vanishing components in both directions, parallel as well as perpendicular to the imposed uniform shear slip, the first being predominant on the second. We perform a set of computations aimed at evaluating the dependence of the tangential displacement magn itude on the relevant fault parameters for basic cases of rectangular faults embedded in a homogeneous half-space. [ABSTRACT FROM AUTHOR]

Sonic log records, including measurements of wave speeds in boreholes, provide critical input to the geological, geophysical, and petrophysical studies of a region under exploration. 1D background models are routinely built based on sonic log records for applications such as seismic imaging of hydrocarbon reservoirs and microseismic source inversions. Smoothing or 'upscaling' techniques are required to produce models in coarser scales than the very fine layers in the raw log data. In this paper, we follow the recently popular homogenization theory, derive its application to the special case of 1D TI models for both P-SV and SH waves, and show that it is consistent with the Backus averaging technique commonly used to upscale 1D fine-layered models. We examine a study case of sonic log data from a well in the Horn River Basin in northeastern British Columbia, a region known for its tight shale-gas deposit. We demonstrate the computational accuracy and efficiency gained by proper upscaling procedures for spectral-element simulations of seismic wave propagation, and discuss the effect of control parameters on wavefield recovery. [ABSTRACT FROM AUTHOR]

Crustal gravitational potential energy (GPE) change induced by earthquakes is an important subject in geophysics and seismology. For the past forty years the research on this subject stayed in the stage of qualitative estimate. In recent few years the 3D dynamic faulting theory provided a quantitative solution of this subject. The theory deduced a quantitative calculating formula for the crustal GPE change using the mathematic method of tensor analysis under the principal stresses system. This formula contains only the vertical principal stress, rupture area, slip, dip, and rake; it does not include the horizontal principal stresses. It is just involved in simple mathematical operations and does not hold complicated surface or volume integrals. Moreover, the hanging wall vertical moving (up or down) height has a very simple expression containing only slip, dip, and rake. The above results are significant to investigate crustal GPE change. Commonly, the vertical principal stress is related to the gravitational field, substituting the relationship between the vertical principal stress and gravitational force into the above formula yields an alternative formula of crustal GPE change. The alternative formula indicates that even with lack of in situ borehole measured stress data, scientists can still quantitatively calculate crustal GPE change. The 3D dynamic faulting theory can be used for research on continental fault earthquakes; it also can be applied to investigate subduction earthquakes between oceanic and continental plates. Subduction earthquakes hold three types: (a) crust only on the vertical up side of the rupture area; (b) crust and seawater both on the vertical up side of the rupture area; (c) crust only on the vertical up side of the partial rupture area, and crust and seawater both on the vertical up side of the remaining rupture area. For each type we provide its quantitative formula of the crustal GPE change. We also establish a simplified model (called CRW Model) as follows: for Type B and Type C subduction earthquakes, if the seawater average depth on the vertical up side of the rupture area is less than a tenth of the hypocenter depth, then take the approximation that the seawater above the continental plate is replaced by the upper crustal material of the continental plate. The formula of quantitative calculating the crustal GPE change is also provided for this model. Finally, for 16 September 2015 Mw 8.3 Illapel Chile earthquake, we apply CRW Model and obtain the following results: the crustal GPE change is equal to 1.8 × 10 J, and the hanging wall vertical moving-up height is 1.9 m with respect to the footwall. We believe this paper might be the first report on the quantitative solution of the crustal GPE change for this subduction earthquake; our results and related method will be helpful in research into the earthquakes in Peru-Chile subduction zone and the Andean orogeny. In short, this study expounds a new method for quantitative determining the crustal GPE change caused by subduction earthquakes, which is different from other existing methods. [ABSTRACT FROM AUTHOR]

The joint use of multiple geophysical data types has been proven to be a powerful tool to both improve subsurface imaging and help in the interpretation process. The main goal of this paper is to develop a multi-geophysical approach for subsurface experimental investigations in which seismic data are used to improve electrical resistivity tomography quality. The basic philosophy of the method is that seismic travel time data will be used to construct the prior model for the resistivity inversion. Synthetic data were employed to demonstrate the improvements enabled by the use of this strategy. Afterwards, the scheme was applied successfully on field data from northwestern China. The outcomes reveal that the multi-geophysical approach improves the interpretation of the subsurface over a single source. [ABSTRACT FROM AUTHOR]

The 16 September 2015 Illapel, Chile, earthquake and associated tsunami have been studied by many researchers from various aspects. This paper reviews studies on the source model of the earthquake and examines tsunami data. The Illapel earthquake occurred in the source region of previous earthquakes in 1943 and 1880. The earthquake source was studied using various geophysical data, such as near-field seismograms, teleseismic waveform and backprojection, GPS and InSAR data, and tsunami waveforms. Most seismological analyses show a duration of ~100 s with a peak at ~50 s. The spatial distribution has some variety, but they all have the largest slip varying from 5 to 16 m located at 31°S, 72°W, which is ~70 km NW of the epicenter. The shallow slip seems to be extended to the trench axis. A deeper slip patch was proposed from high-frequency seismic data. A tsunami earthquake model with a total duration of 250 s and a third asperity south of the epicenter is also proposed, but we show that the tsunami data do not support this model. [ABSTRACT FROM AUTHOR]

By introducing a residual geometrical spreading factor, a new model was proposed in recent papers of Morozov to improve the estimates of seismic Q, and some published seismic Q observations were reinterpreted under the framework of the new model. We found that in these papers the definitions about the residual geometrical spreading and seismic scattering attenuation were conceptually confusing, and physically impossible negative values of seismic Q may arise in the new model. We argue that the estimates of the residual geometrical spreading in the new model are influenced by seismic scattering. Thus, the correlation between the residual geometrical spreading and tectonic activity, and the observation of temporal variations of the residual geometrical spreading and apparent attenuation, as reported by Morozov, are not surprising. [ABSTRACT FROM AUTHOR]

In this paper, I present a new depth estimation method based on the ratio of gravity and full tensor gradient invariant. The new approach is designed to be stably and quickly interpret the gravity data and full tensor gravity data. First, we deduce two simple calculation equations using the particular models (sphere and horizontal cylinder model). The depths of the particular sources can be directly calculated using the simple equations. However, a shape factor similar to the structural index of Euler deconvolution is contained in the simple calculation equations. It directly relates to the accuracy of calculation depth. To calculate the depth of source accurately, the shape factor must be determined first. Thus, the application of the simple equations is very circumscribed. To overcome the limitation, I calculate the ratio of the simple equations of different altitudes to improve the original algorithm. It effectively eliminates the influence of the shape factor. I use different model to test the method and apply the method on real gravity data. It demonstrates that the new approach is stable, simple and effective depth estimation method. The new improved approach not only can be used to calculate the sphere and cylinder model depth, but also can be used to calculate other general models. It is a very useful tool to calculate the depth of gravity bodies. [ABSTRACT FROM AUTHOR]

Deep-ocean tsunami measurements play a major role in understanding the physics of tsunami wave generation and propagation, and in improving the effectiveness of tsunami warning systems. This paper provides an overview of the history of tsunami recording in the open ocean from the earliest days, approximately 50 years ago, to the present day. Modern tsunami monitoring systems such as the self-contained Deep-ocean Assessment and Reporting of Tsunamis and innovative cabled sensing networks, including, but not limited to, the Japanese bottom cable projects and the NEPTUNE-Canada geophysical bottom observatory, are highlighted. The specific peculiarities of seafloor longwave observations in the deep ocean are discussed and compared with observations recorded in coastal regions. Tsunami detection in bottom pressure observations is exemplified through analysis of distant (22,000 km from the source) records of the 2004 Sumatra tsunami in the northeastern Pacific. [ABSTRACT FROM AUTHOR]

A suitable knowledge of the orientation and motion of the Earth in space is a common need in various fields. That knowledge has been ever necessary to carry out astronomical observations, but with the advent of the space age, it became essential for making observations of satellites and predicting and determining their orbits, and for observing the Earth from space as well. Given the relevant role it plays in Space Geodesy, Earth rotation is considered as one of the three pillars of Geodesy, the other two being geometry and gravity. Besides, research on Earth rotation has fostered advances in many fields, such as Mathematics, Astronomy and Geophysics, for centuries. One remarkable feature of the problem is in the extreme requirements of accuracy that must be fulfilled in the near future, about a millimetre on the tangent plane to the planet surface, roughly speaking. That challenges all of the theories that have been devised and used to-date; the paper makes a short review of some of the most relevant methods, which can be envisaged as milestones in Earth rotation research, emphasizing the Hamiltonian approach developed by the authors. Some contemporary problems are presented, as well as the main lines of future research prospected by the International Astronomical Union/International Association of Geodesy Joint Working Group on Theory of Earth Rotation, created in 2013. [ABSTRACT FROM AUTHOR]

In this paper, we study the motion of a fluid with several dispersed particles whose concentration is very small (smaller than $$10^{-3}$$ ), with possible applications to problems coming from geophysics, meteorology, and oceanography. We consider a very dilute suspension of heavy particles in a quasi-incompressible fluid (low Mach number). In our case, the Stokes number is small and-as pointed out in the theory of multiphase turbulence-we can use an Eulerian model instead of a Lagrangian one. The assumption of low concentration allows us to disregard particle-particle interactions, but we take into account the effect of particles on the fluid (two-way coupling). In this way, we can study the physical effect of particles' inertia (and not only passive tracers), with a model similar to the Boussinesq equations. The resulting model is used in both direct numerical simulations and large eddy simulations of a dam-break (lock-exchange) problem, which is a well-known academic test case. [ABSTRACT FROM AUTHOR]

Geosystemics is a way to see and study the Earth in its wholeness together with the eventual couplings among the subsystems composing our planet. This paper will provide this view for the Earth's magnetic field, reviewing most of the results obtained in our recent works. The main tools used by geosystemics are some nonlinear quantities, such as some kinds of entropy. Through them, it is possible to: (a) establish the chaoticity and ergodicity of the recent geomagnetic field in a direct and simple way; and (b) indentify the most extreme events in its history, as the most rapid and the slowest ones, i.e., jerks and polarity changes (reversals or excursions). In particular, regarding the latter phenomena, with the help of these entropic concepts and together with the use of the theory of critical transitions, some clues can be given for a possible imminent change of the geomagnetic field dynamical regime. [ABSTRACT FROM AUTHOR]

This paper describes a method for interpreting the lateral changes in the geological structure of the lithosphere by iteratively calculating the spatial variation of a bottom-to-top loading ratio. We use Forsyth's coherence method, based on multi-taper spectral analysis on overlapping window areas. We discuss the geological findings and their comparison with existing geological interpretations for the Sri Lankan region. The low thickness of the elastic plate in the Sri Lankan region suggests a high geothermal gradient. The lithospheric geological structure beneath the Sri Lankan region is consistent with the main crustal units of Sri Lanka, which belong to different ancient plates. Together with interpretations based on metamorphic rock units, our findings support the existence of thrust contact in the central highlands of Sri Lanka. [ABSTRACT FROM AUTHOR]

Orthoimage maps have become very popular and frequently produced cartographical outputs in geosciences during recent years. However, the unambiguous terminology, definitions, content and appearance specifications have not been widely researched. This paper deals with the new definition of the orthoimage map, its component delineation, and basic classification. The authors present aspects of topographic and thematic orthoimage maps. The main theoretical achievement of the authors' research is the determining of the image component and the symbol component of orthoimage map content. The presented orthoimage map concept is applicable in geophysics practise which is demonstrated by three presented topographic and thematic orthoimage maps. They differ according to the relationship between topographic background and thematic content, and between image and symbol component. The image component can be a carrier of thematic geophysical information, or it can be used as topographic background for geophysics-oriented symbol component. All prototypes give examples of how to design, complete and use image-based cartographical products. Those variants might be used as guidelines for future orthoimage map production, especially for the geophysics community. [ABSTRACT FROM AUTHOR]

The thermal hot springs of Caldas de Monção, located in Northern Portugal, are supplied by a thermal water aquifer that must be preserved from pollution and anthropic effects. Enhancement of knowledge about the aquifer is therefore needed, so sustainable management and water quality preservation can be conducted, namely by replacing the springs by boreholes, which are less vulnerable to pollution. Several investigations have been conducted with this purpose, to review the available geological and hydrogeological information from the area. For this reason, several geophysical surveys were reprocessed and others were acquired and planned, so that a 3D conceptual groundwater flow model of could be drawn. Three seismic reflection profiles were acquired with the objective of locating deep faults capable of transporting groundwater to the surface and to complement information about shallow features available before the seismic survey. This information included interpretation of a dipole-dipole survey conducted in 2001, that reached an investigation depth of approximately 40 m, and two shallow boreholes drilled, after a deeper geoelectrical survey performed in the 1980s, to replace the springs. Besides the seismic reflection profiles, seven vertical electrical soundings were also acquired and refraction interpretation of the first reflection data to arrive was also undertaken to complement the information. This paper reports integrated interpretation of the geophysical and geological data to obtain a 3D conceptual model to achieve the above mentioned objectives. After interpretation and lateral correlation of the structures found in the geophysical profiles, the deep 3D conceptual model integrating the geological, hydrogeological, and geophysical information was constructed. This model was the basis for planning the location of an exploratory borehole that was drilled afterwards. From two initial locations appearing as the strongest candidates for a successful thermal water production well, one was chosen to drill a third borehole to supply the spa facilities. The third borehole results were very positive-250 m deep, temperature approximately 50°C, and water flow 12.5 l/s. This example shows the utility of using geophysical methods to increase knowledge about groundwater circulation and detect favourable areas for thermal water borehole drilling to replace the hot springs with the objective of protecting the aquifer from pollution. [ABSTRACT FROM AUTHOR]

A pseudo-seismic interpretation method is an alternative way to process and explain transient electromagnetic (TEM) data, and has become a popular research field in recent years. TEM signals which satisfy the diffusion equation can be converted by means of a mathematical transformation into ones which obey the wave equation. For an ill-posed problem of this kind of transformation, a sub-regularization algorithm is developed in this paper to extract a virtual wavelet of the TEM field. According to the conventional designation of TEM recordings, the entire integration period is divided into seven time intervals. In order to avoid low accuracy in the calculations, high-density wavefield data has been calculated based on the former sub-division. Therefore, the virtual wavelet can be extracted successfully by using an optimized algorithm to obtain high-density integral coefficients for all time windows, and a satisfactory condition number of the coefficient matrix while taking a different channel number in each time period. The Tikhonov regularization inversion scheme is used to determine the optimal parameters based on minimizing a least squares misfit, and the Newton iterative formula is used to obtain optimal regularization parameters. Both synthetic model simulations and a real data interpretation example indicate that the proposed pseudo-seismic wavefield method is a suitable alternative way to interpret TEM data. [ABSTRACT FROM AUTHOR]

The Algarve province is located a few hundred kilometres north of the crossing of the E-W Eurasia-Africa plate boundary in an area of diffuse seismicity and broad deformation. It is characterised by a moderate seismicity, with some important historical and instrumental earthquakes causing loss of lives and significant material damages. The area is affected not only by plate boundary earthquakes but also by moderate to large events generated by local sources. The assessment of onshore local sources is, therefore, of vital importance for an evaluation of the regional seismic hazard. This paper discusses the application of geophysical data to the study of the Carcavai fault zone, an outcropping structure more than 20 km long which is seen to deform sediments of the Plio-Quaternary age. The location of some sectors of the fault zone, as well as the vertical offsets of the structure, are still to be confirmed. In order to estimate these and to study the geometry of the fault zone at depth, geophysical data were acquired together with new geological data. Where the location of the fault was less certain, EM and seismic reflection profiles with coarse spatial sampling were carried out. After the detailed location of the fault zone, seismic reflection profiles with a more dense spatial resolution were acquired. The integrated interpretation of the geological and geophysical data confirmed the presence of a large fault zone. The total fault length is still unknown as its extension offshore is still being studied. Together with estimated values of the throw obtained, this data set has improved understanding the seismic hazard in the area by providing more refined estimates of co-seismic rupture, maximum expected earthquake and return periods. [ABSTRACT FROM AUTHOR]

This paper presents the effects of impedance contrast (IC) across the basin edge, velocity contrast between the basin and underlying bedrock, Poisson's ratio and soil thickness on the characteristics of basin-transduced Rayleigh (BTR) waves and associated differential ground motion (DGM). Analysis of simulated results for a two-dimensional (2D) basin revealed complex mode transformation of Rayleigh waves after entering the basin. Excellent correlation of frequencies corresponding to different spectral ratio peaks in ellipticity curves of BTR waves and spectral amplification peaks was obtained. However, such correlation was not observed between values of peaks in ellipticity curves and spectral amplification at the corresponding frequencies. An increase of spectral amplification with IC was obtained. The largest spectral amplification was more than twice the IC in the horizontal component and more than the IC in the vertical component in the case of large and same impedance contrast for P- and S-waves. It was concluded that the frequency corresponding to the largest spectral amplification was greater than the fundamental frequency of soil by around 14% and 44% in the vertical and horizontal components, respectively. Spectral amplification of the vertical component was negligible when soil thickness was less than around 15-20 times the S-wave wavelength in the basin. The largest values of peak ground displacement (PGD) and peak differential ground motion (PDGM) were obtained very near the basin edge, and their values with offset from the edge were strongly dependent on the IC across the basin edge, Poisson's ratio, velocity contrast between the basin and underlying bedrock (dispersion), damping and soil thickness. The obtained value of PDGM for a span of 50 m in the horizontal and vertical components due to the BTR wave was of the order of 0.75 × 10 and 1.32 × 10 for unit amplitude (1.0 cm) in the horizontal component of the Rayleigh wave at rock very near the basin edge. [ABSTRACT FROM AUTHOR]

Izmir, the third largest city and one of the major economic centers in Turkey, has more than three million residents and one-half million buildings. The city, located in a seismically active region in western Anatolia, was a subject of the 1997 RADIUS (Risk Assessment Tools for Diagnosis of Urban Areas against Seismic Disaster) project. In this paper, the seismic hazard of Izmir is investigated through probabilistic seismic hazard assessment. First, the seismic setting of Izmir is presented. Considering the statistics of earthquakes that took place in the region during the period 1900-2005, a simple seismic hazard model is used to facilitate the assessment. To account for modeling uncertainties associated with the values of seismicity parameters, a logic tree procedure is employed in carrying out the seismic hazard computations. The resulting weighted average seismic hazard, presented in terms of peak ground acceleration and associated probability of exceedence, could be considered the 'best estimate' of seismic hazard for Izmir. Accordingly, for a return period of 475 years, for rock sites, a PGA value of 0.34 g is calculated. This PGA hazard estimate is close to the current code-recommended design acceleration level for Izmir. [ABSTRACT FROM AUTHOR]

The South Atlantic magnetic Anomaly (SAA) is an important feature of the present geomagnetic field. In this paper we model the space–time evolution of this anomaly over the past 400 years in terms of the resultant between a decrease of a global axial dipole and an increase of a virtual local monopole source. Certain characteristics of this evolution are investigated and some considerations are made in the light of a possible special state of the global geomagnetic field dynamical regime. Among the possible speculations, one is made regarding the topography of the core-mantle boundary (CMB) and its possible aspect beneath the SAA region in terms of simple sinusoidal undulations met by the monopole source during its centennial motion. [ABSTRACT FROM AUTHOR]

Ring Laser gyroscopes exploit the Sagnac effect and measure rotations absolute. They do not require an external reference frame and therefore provide an independent method to monitor Earth rotation. Large-scale versions of these gyroscopes promise to eventually provide a similar high resolution for the measurement of the variations in the Earth rotation rate as the established methods based on VLBI and GNSS. This would open the door to a continuous monitoring of LOD (Length of Day) and polar motion, which is not yet available today. Another advantage is the access to the sub-daily frequency regime of Earth rotation. The ring laser “G” (Grossring), located at the Geodetic Observatory Wettzell (Germany) is the most advanced realization of such a large gyroscope. This paper outlines the current sensor design and properties. [ABSTRACT FROM AUTHOR]

We present a systematic and unified treatment of Earth rotation from the geodetic, astronomical, and geophysical point of view. A precise terminology of precession-nutation and polar motion is of great importance for understanding the interacting physical phenomena leading to rotational irregularities of the Earth. In total, four poles of the equatorial plane are defined for the description of Earth rotation. The various components of the Earth Orientation Parameters, i.e., precession-nutation, polar motion, and universal time (or length of day) are summarized. This paper shows how very long baseline interferometry and ring laser differ in terms of Earth rotation and presents the current state-of-the-art measurement accuracy that can be achieved. [ABSTRACT FROM AUTHOR]