Geophysical prospecting in the Krousovitis dam (N. Greece) by seismic and resistivity methods

Abstract: The use of two geophysical methods in the investigation of the geological setting in the area of a dam foundation is presented in this study. The seismic method was used in order to map the structure of the upper layers near the riverbed. VES and resistivity tomographs were also carried out. The depth to the basement was estimated by interpreting the VES curves. Interpretation of the topographic images, along with the inferred models from the seismic data, revealed the thickness of the colluvial deposits

Preliminary report on the M4.9 Earthquake in Culberson-Reeves County Line

On March 26th, 2020 at 3:16pm (Local Time) an earthquake of ML 4.6 (MW 4.9) occurred in west Texas along the Culberson-Reeves County Line (CRCL). This is a preliminary report on this event

Absolute earthquake location in west Texas using probabilistic, proxy ground-truth station corrections

This repository contains data files used in the research paper published in Journal of Geophysical Research in 2019: Improving absolute earthquake location in west Texas using probabilistic, proxy ground-truth station corrections Anthony Lomax - ALomax Scientific, Mouans-Sartoux, France. Alexandros Savvaidis - Bureau of Economic Geology, The University of Texas at Austin, Austin, TX. The repository contains a set of spreadsheets with earthquake catalog information calculated following the processes described in the above paper. These results are used to produce Figures 5 and 15 of the paper. Comma separated (.csv) file format is used for the spreadsheets

The spatial distribution of causal factors behind the seismicity in the Delaware basin

Our analysis hindcasts seismicity rates of magnitude (M) ≥ 1.5 in the Delaware Basin (West Texas) from 2017 through 2019 on a 5km grid using either HF or SWD data as input, and compares them against the null hypothesis of solely tectonic loading. Each block is assigned a p-value, indicating the statistical confidence of its causal link with either HF, shallow SWD or deep SWD injection operations. To do that we expanded the framework of Grigoratos et al. (2020) to daily hydraulic fracturing (HF) operations and pressure-driven modeling of wastewater disposal (SWD). Our results indicate that 60% of the earthquakes occurred in blocks with p ≤ 0.05 (95% confidence interval) for at least one examined causal factor, and are thus triggered by oil and gas activities. This percentage increases to 68% for p ≤ 0.10 (90% confidence interval). Overall, more events than previously identified are associated with HF, especially within Reeves county. That said, shallow SWD is linked to more earthquakes, likely reactivating parallel faults of significant length. The seismicity around Pecos city seems to be affected by more than one injection activity, with higher frequency operational data and better depth resolution needed to fully decouple causality. Finally, within Culberson county, the only area where the earthquakes occur predominantly within the basement, the identified triggering mechanism is far-field SWD from deep wells

Classification of topography using dem data and its correlation with the geology of Greece

Proceedings of SPIE - The International Society for Optical Engineering, Volume 8795, 2013, Article number 87950SContinuous topography from Digital Elevation Model (DEM) data is frequently segmented into terrain classes based on local morphological characteristics of terrain elevation, e.g., local slope gradient and convexity. The resulting classes are often used as proxies for the average shear wave velocity up to 30 m, and the determination of ground types as required by the Eurocode (EC8) for computing elastic design spectra. In this work, we investigate the links between terrain related variables, particularly slope gradient, extracted for the area of Greece from the Shuttle Radar Topography Mission (SRTM) 30 arc second global topographic data available from the United States Geological Survey (USGS), with: (a) the global terrain classification product of Iwahashi and Pike (2007) in which 16 terrain types are identified for the same spatial resolution, and (b) information on geological units extracted at the same resolution from the geological map of Greece at a scale of 1/500000 as published from the Institute of Geology and Mineral Exploration (IGME). An interpretation of these links is presented within the context of understanding the reliability of using geology, slope and terrain classes for site characterizations of earthquake risk in a high seismicity area like Greece. Our results indicate that slope is a somewhat biased proxy for solid rocks, whereas in Alluvial deposits the distance to and type of the nearest geological formation appears to provide qualitative information on the size of the sedimentary deposit. © 2013 SPIE

Onset and Cause of Increased Seismic Activity Near Pecos, West Texas, United States, From Observations at the Lajitas TXAR Seismic Array

In recent years, numerous small earthquakes have occurred near the town of Pecos in West Texas; however, when this activity began and whether it was caused by increased petroleum industry activity has been uncertain because prior to 2017 there were few permanent seismograph stations in the region. We identify and locate earthquakes using data recorded since 2000 at TXAR, a sensitive 10‐station seismic array situated about 240 km south of Pecos. We thus show that in 2007, one earthquake occurred near Pecos, in 2009 several more occurred, and subsequently, activity has increased considerably, with more than 2000 events identified in 2017. A time‐of‐day and year‐by‐year analysis identifies geographic areas in West Texas where events are likely to be natural earthquakes and quarry blasts. However, for the Pecos events, annual seismicity rates increase along with annual volumes of petroleum production and fluid waste disposal, suggesting a causal link. Analysis of seismograms collected by the EarthScope Transportable Array indicates that the 2009 earthquakes had focal depths of 4.0–5.2 km below sea level, within or just below strata where petroleum is produced and/or wastewater is injected. The largest earthquake to date had magnitude ML3.7, but the recent high activity rates suggest that greater magnitudes may be possible. For the years 2000–2017, we provide a catalog of 10,753 epicenters of seismic events recorded at TXAR