Geological Criteria for Evaluating seismicity revisited: Forty Years of Paleoseismic Investigations and the Natural Record of Past Earthquakes

The identifi cation of individual past earthquakes and their characterization in time and space, as well as in magnitude, can be approached in many different ways with a large variety of methods and techniques, using a wide spectrum of objects and features. We revise the stratigraphic and geomorphic evidence currently used in the study of paleoseismicity, after more than three decades since the work by Allen (1975), which was arguably the fi rst critical overview in the fi eld of earthquake geology. Natural objects or geomarkers suitable for paleoseismic analyses are essentially preserved in the sediments, and in a broader sense, in the geologic record. Therefore, the study of these features requires the involvement of geoscientists, but very frequently it is a multidisciplinary effort. The constructed environment and heritage, which typically are the focus of archaeoseismology and macroseismology, here are left aside. The geomarkers suitable to paleoseismic assessment can be grouped based on their physical relation to the earthquake\u2019s causative fault. If directly associated with the fault surface rupture, these objects are known as direct or on-fault features (primary effects in the Environmental Seismic Intensity [ESI] 2007 scale). Conversely, those indicators not in direct contact with the fault plane are known as indirect or off-fault evidence (secondary effects in the ESI 2007 scale). This second class of evidence can be subdivided into three types or subclasses: type A, which encompasses seismically induced effects, including soft-sediment deformation (soil liquefaction, mud diapirism), mass movements (including slumps), broken (disturbed) speleothems, fallen precarious rocks, shattered basement rocks, and marks of degassing (pockmarks, mud volcanoes); type B, which consists of remobilized and redeposited sediments (turbidites, homogenites, and tsunamites) and transported rock fragments (erratic blocks); and type C, entailing regional markers of uplift or subsidence (such as reef tracts, microatolls, terrace risers, river channels, and in some cases progressive unconformities). The fi rst subclass of objects (type A) is generated by seismic shaking. The second subclass (type B) relates either to water bodies set in motion by the earthquake (for the sediments and erratic blocks) or to earthquake shaking; in a general way, they all relate to wave propagation through different materials. The third subclass (type C) is mostly related to the tectonic deformation itself and can range from local (next to the causative fault) to regional scale. The natural exposure of the paleoseismic objects\u2014which necessarily conditions the paleoseismic approach employed\u2014is largely controlled by the geodynamic setting. For instance, oceanic subduction zones are mostly submarine, while collisional settings tend to occur in continental environments. Divergent and wrenching margins may occur anywhere, in any marine, transitional, or continental environment. Despite the fact that most past subduction earthquakes have to be assessed through indirect evidence, paleoseismic analyses of this category of events have made dramatic progress recently, owing to the increasingly catastrophic impact that they have on human society

Future trends in paleoseismology: Integrated study of the seismic landscape as a vital tool in seismic hazard analyses

This paper forms the Introduction to this Special Issue of Tectonophysics, devoted to selected scientific research presented during events sponsored by the INQUA Subcommission on Paleoseismicity in the past few years. In this note, we summarize the contents of the contributed papers and use the issues they raise to review the state-of-the-art in paleoseismology from a Quaternary geology perspective. In our opinion, the evolution of paleoseismological studies in the past decade clearly demonstrates that in order to properly understand the seismic potential of a region, and to assess the associated hazards, broad-based/multidisciplinary studies are necessary to take full advantage from the geological evidence of past earthquakes. A major challenge in future paleoseismic research is to build detailed empirical relations between various categories of coseismic effects in the natural environment and earthquake magnitude/ intensity. These relations should be compiled in a way that is fully representative of the wide variety of natural environments on Earth, in terms of climatic settings, Quaternary tectonic evolution, rheological parameters of the seismogenic crust, and stress environment. For instance, available data indicate that between earthquake magnitude and surface faulting parameters different scaling laws exist, and they are a function of the local geodynamic setting (including style of faulting, typical focal depths, heat flow). In this regard, we discuss in some detail the concept of seismic landscape, which provides the necessary background for developing paleoseismological research strategies. The large amount of paleoseismological data collected in recent years shows that each earthquake source creates a signature on the geology and the geomorphology of an area that is unequivocally related with the order of magnitude of its earthquake potential. This signature is defined as the seismic landscape of the area (e.g., Serva, L., Vittori, E., Ferreli, L., Michetti, A.M., 1997. Geology and seismic hazard. In: Grellet, B., Mohammadioun, B., Hays, W. (Eds.), Proceedings of the Second France\u2013United States Workshop on Earthquake Hazard Assessment in Intraplate Regions: Central and Eastern United States and Western Europe, October 16, 1995, Nice, France, 20\u201324, Ouest Editions, Nantes, France; Michetti, A.M., Hancock, P.L., 1997. Paleoseismology: understanding past earthquakes using quaternary geology Journal of Geodynamics 24 (1\u20134), 3\u201310). We then illustrate how this relatively new framework is helpful in understanding the seismic behavior of faults capable of producing surface faulting and provides a comprehensive approach for the use of paleoseismicity data in earthquake hazard characterization

Paleoseismology, integrated study of the Quaternary geological record for earthquake deformation and faulting

Tectonophysics 408 (2005) v\u2013 vi, Special Issue Paleoseismology: Integrated study of the Quaternary geological record for earthquake deformation and faulting, doi:10.1016/S0040-1951(05)00465-

Automated Benchmarking of Incremental SAT and QBF Solvers

Incremental SAT and QBF solving potentially yields improvements when sequences of related formulas are solved. An incremental application is usually tailored towards some specific solver and decomposes a problem into incremental solver calls. This hinders the independent comparison of different solvers, particularly when the application program is not available. As a remedy, we present an approach to automated benchmarking of incremental SAT and QBF solvers. Given a collection of formulas in (Q)DIMACS format generated incrementally by an application program, our approach automatically translates the formulas into instructions to import and solve a formula by an incremental SAT/QBF solver. The result of the translation is a program which replays the incremental solver calls and thus allows to evaluate incremental solvers independently from the application program. We illustrate our approach by different hardware verification problems for SAT and QBF solvers.Comment: camera-ready version (8 pages + 2 pages appendix), to appear in the proceedings of the 20th International Conference on Logic for Programming, Artificial Intelligence and Reasoning (LPAR), LNCS, Springer, 201

Magnitude estimation of the 1900 earthquake in Venezuela based on its coseismic effects

The 29 October, 1900, earthquake occurred in Venezuela triggered six landslides and six liquefactions located in the center-north region of Venezuela and La Tortuga island. Due to the location of the coseismic effects, the barycenter and the focal depth related to this earthquake, it was possible to calculate the magnitude by using several statistical methods. The results show a magnitude in the range 7.4-7.7 Mw, with an average value equal to 7.6 Mw, which is consistent with the instrumental magnitude of 7.6 Mw obtained by Fiedler (1988) and the macrosismic magnitude by Vásquez et al. (2018) equal to 7.5 ± 0.3 Mw estimated by using the Bakun and Wentworth (1997) method

Morphotectonic interpretation of the Ibague fault for paleoseismological purposes

The Ibagué Fault is a WSW-ENE right-lateral strike-slip structure located in the central part of the Central Cordillera and in the middle of transverse shear zone that affects the Colombian Andes. Morphotectonic interpretations of the fault from satellite images allow us to propose the style of deformation and the kinematics of the structure. These structural characteristics together with geographical, geomorphologic, sedimentologic and climatic data are key elements for the right selection of a paleoseismical investigation site. The strand appears to be as a single line along the Ibagué Fan at regional scale. However, detailed studies shown several morphotectonic features characteristic of wrench tectonics. Riedel and en-echelon array indicate dextral displacements. Additionally, microtectonic data show a local stress tensor with a s1=311º/18 °±15 ° and a factor R=0,62, indicating a strike-slip regime, which is coherent with the observed geologic and morphotectonic features.  La Falla Ibagué es una estructura de tipo transcurrente dextral que se extiende en dirección WSW-ENE y se encuentra ubicada en medio de una zona de cizalla transversal que afecta la parte central de la Cordillera Central de Los Andes Colombianos con dirección NEE. Utilizando imágenes de sensores remotos se realizó una interpretación morfotectónica de la falla, que permitió proponer la geometría de deformación y algunas características cinemáticas, conocimiento que, junto con datos geográficos, morfoclimáticos y sedimentológicos, es básico para la elección acertada de un sitio de trinchera de exploración paleosismológica. El trayecto de la falla a lo largo del Abanico de Ibagué se muestra regionalmente como un solo trazo, pero a mayor escala se observan numerosos y variados rasgos morfotectónicos característicos de fallamiento transcurrente, caracterizados por presentar un arreglo de cizallas Riedel dextrales y en echelon con saltos a la izquierda. Las mediciones microtectónicas en estaciones situadas a lo largo de la falla en el Abanico de Ibagué arrojaron un tensor de esfuerzos local, con un esfuerzo máximo horizontal (s1) de dirección 311º/18° +/- 15° y un factor de forma de R=0,62, que indican un régimen de esfuerzos de tipo transcurrente, resultado que es consecuente con las observaciones morfotectónicas y geológicas.  &nbsp

Incremental QBF Solving

We consider the problem of incrementally solving a sequence of quantified Boolean formulae (QBF). Incremental solving aims at using information learned from one formula in the process of solving the next formulae in the sequence. Based on a general overview of the problem and related challenges, we present an approach to incremental QBF solving which is application-independent and hence applicable to QBF encodings of arbitrary problems. We implemented this approach in our incremental search-based QBF solver DepQBF and report on implementation details. Experimental results illustrate the potential benefits of incremental solving in QBF-based workflows.Comment: revision (camera-ready, to appear in the proceedings of CP 2014, LNCS, Springer

Incrementally Computing Minimal Unsatisfiable Cores of QBFs via a Clause Group Solver API

We consider the incremental computation of minimal unsatisfiable cores (MUCs) of QBFs. To this end, we equipped our incremental QBF solver DepQBF with a novel API to allow for incremental solving based on clause groups. A clause group is a set of clauses which is incrementally added to or removed from a previously solved QBF. Our implementation of the novel API is related to incremental SAT solving based on selector variables and assumptions. However, the API entirely hides selector variables and assumptions from the user, which facilitates the integration of DepQBF in other tools. We present implementation details and, for the first time, report on experiments related to the computation of MUCs of QBFs using DepQBF's novel clause group API.Comment: (fixed typo), camera-ready version, 6-page tool paper, to appear in proceedings of SAT 2015, LNCS, Springe

Morphotectonic interpretation of the Ibague fault for paleoseismological purposes

The Ibagué Fault is a WSW-ENE right-lateral strike-slip structure located in the central part of the Central Cordillera and in the middle of transverse shear zone that affects the Colombian Andes. Morphotectonic interpretations of the fault from satellite images allow us to propose the style of deformation and the kinematics of the structure. These structural characteristics together with geographical, geomorphologic, sedimentologic and climatic data are key elements for the right selection of a paleoseismical investigation site. The strand appears to be as a single line along the Ibagué Fan at regional scale. However, detailed studies shown several morphotectonic features characteristic of wrench tectonics. Riedel and en-echelon array indicate dextral displacements. Additionally, microtectonic data show a local stress tensor with a s1=311º/18 °±15 ° and a factor R=0,62, indicating a strike-slip regime, which is coherent with the observed geologic and morphotectonic features.  La Falla Ibagué es una estructura de tipo transcurrente dextral que se extiende en dirección WSW-ENE y se encuentra ubicada en medio de una zona de cizalla transversal que afecta la parte central de la Cordillera Central de Los Andes Colombianos con dirección NEE. Utilizando imágenes de sensores remotos se realizó una interpretación morfotectónica de la falla, que permitió proponer la geometría de deformación y algunas características cinemáticas, conocimiento que, junto con datos geográficos, morfoclimáticos y sedimentológicos, es básico para la elección acertada de un sitio de trinchera de exploración paleosismológica. El trayecto de la falla a lo largo del Abanico de Ibagué se muestra regionalmente como un solo trazo, pero a mayor escala se observan numerosos y variados rasgos morfotectónicos característicos de fallamiento transcurrente, caracterizados por presentar un arreglo de cizallas Riedel dextrales y en echelon con saltos a la izquierda. Las mediciones microtectónicas en estaciones situadas a lo largo de la falla en el Abanico de Ibagué arrojaron un tensor de esfuerzos local, con un esfuerzo máximo horizontal (s1) de dirección 311º/18° +/- 15° y un factor de forma de R=0,62, que indican un régimen de esfuerzos de tipo transcurrente, resultado que es consecuente con las observaciones morfotectónicas y geológicas.  &nbsp

La depresión submarina de Guaracayal, estado Sucre, Venezuela: Una barrera para la propagación de la ruptura cosísmica a lo largo de la falla de el pilar

La depresión de Guaracayal, en el golfo de Cariaco, estado Sucre, Venezuela, fue inicialmente reconocida a partir de un levantamiento batimétrico realizado en la década de los ochenta. Un levantamiento de sísmica somera de alta resolución adquirido en el golfo de Cariaco a bordo del B/O Guaiquerí II en enero 2006 reveló que esta depresión resulta ser una cuenca en tracción activa (“active pull-apart basin”) sobre la traza activa submarina de la falla dextral de El Pilar, por su geometría y lo fresco y prominente de los escarpes de fallas que la limitan. Esta cuenca, con una profundidad de aguas de ~15m mayor que el fondo plano ubicado a unos -80m, mide aproximadamente 8km de longitud en dirección este-oeste y unos 2km transversalmente. La cuenca se forma en un relevo dextro, es decir transtensivo, de la traza submarina de la falla de El Pilar, que secciona en dos porciones lo propuesto anteriormente como un único segmento de falla con extensión entre Cumaná y Casanay-Guarapiche. Esta separación entre ambas trazas de 2km parece ser suficiente barrera para la propagación lateral de la ruptura sísmica, tal como lo evidencia la sismicidad contemporánea e histórica. El tramo de falla Cumaná-Casanay, de unos 80km de longitud, ha requerido en dos ocasiones de la conjunción de dos sismos contiguos en dirección oeste-este (1797-1684 y 1929-1997) para romperse en su totalidad. No obstante, no se excluye la posibilidad de un evento que rompa toda la extensión del segmento, a pesar de este comportamiento sísmico reiterado