The classic failed continental rift or aulacogen is one that intersects a rifted continental margin at a high angle. Based on recent geological and geophysical studies, we have revisited a classic analogy that was drawn between two major intracratonic rifts, the Southern Oklahoma aulacogen in the southern portion of Laurentia and the Dniepr-Donets aulacogen in the southern portion of Baltica. The Southern Oklahoma aulacogen, also known as the Wichita aulacogen, consists of a linear alignment of extensively inverted rift structures that begins at the rifted margin of Laurentia in northeast Texas and extends northwestward at least to southern Colorado. Deep seismic profiles have revealed the upper crustal structure of this feature, and gravity data provide a regional context for interpreting these results. Velocities low enough to indicate the presence of sedimentary rocks extend to a depth of ∼15 km, and the deepest of these sedimentary layers has been interpreted as rift fill. In addition, the main inversion structure of the Southern Oklahoma aulacogen (Wichita uplift) is underlain by very high-velocity and dense mafic material even at upper crustal depths of ∼5 km. The Dniepr-Donets aulacogen has been cited as a type example of an aulacogen and is clearly a “failed rift” in the sense that it did not itself lead to continental breakup and ocean crust formation. The main feature of the aulacogen is a Late Devonian rift basin overlain by a substantial (but variable) postrift sedimentary sequence that records several extensional or transtensional events and at least one moderate compressional reactivation. Recent deep seismic reflection and refraction surveys resolve the geometry of the sedimentary succession in the Donets segment of the basin, indicating an asymmetric form with a steeper basement surface in the south than in the north and a total sedimentary thickness of ∼20 km. A thick (>10 km) high-velocity (>6.9 km/s) lower crustal body lies beneath the rift basin itself and is offset slightly to the north compared to the main basin depocenter. The Moho displays only slight topography around a depth of 40 km although, based on older deep seismic data, it shallows somewhat under the rift axis in the Dniepr segment to the northwest. Thus, major differences between these two major rifts are the nature of the magmatic modification of the crust and degree of inversion. Both the age of initial rifting and subsequent inversion in the Dniepr-Donets aulacogen are redefined compared to what was thought at the time the original analogy was made with the Southern Oklahoma aulacogen.

The European portion of the Eurasian plate formed as a result of a complex series of tectonic events that included the Caledonian, Variscan, and Carpathian orogenies. These orogenic events occurred along the western margin of the East European craton (a portion of the paleocontinent Baltica). In recognition of the complexity of the rifting that formed this margin in the Neoproterozoic-Cambrian and the subsequent tectonic events along it, the region adjacent to this margin has been called the Trans-European suture zone. In order to understand the processes at work during these tectonic events, a series of large integrated geophysical and geological investigations built around large seismic refraction-experiments (POLONAISE'97, CELEBRATION 2000, ALP 2002, and SUDETES 2003) were conducted between 1997 and 2003. In this study, we compare the results of the two longest seismic profiles and their tectonic implications. These studies showed that lithospheric structure of the East European craton directly inboard of its margin is relatively uniform, and the crust consists of three layers below the sedimentary cover, and it is ∼45 km thick. The lithospheric mantle contains several reflectors, and its velocity is ∼8.2 km/s. In the Variscides (Paleozoic platform) of northern Poland along the Trans-European suture zone, the consolidated crust beneath the sedimentary cover consists of two distinct layers, and the total crustal thickness is 30–35 km. Within the core region of the Trans-European suture zone, the crust is ∼40 km thick, but most of its upper half is the sedimentary fill of the late Paleozoic and Mesozoic Polish trough, which is underlain by a thick sequence of older continental-margin volcanic and sedimentary units. The lithospheric mantle structure is complex and indicative of a plate collision under the Trans-European suture zone region, and it has seismic velocities that are generally higher than those of the East European craton. In the Carpathian region, the effects of younger collisions are present in addition to evidence of the Variscan orogeny. It is somewhat surprising that the crustal thickness beneath the Carpathians is 30–40 km, but it is not surprising that beneath the Pannonian Basin, an extensional feature, the crust is only 24–28 km thick. The thickest crust in this region (∼50 km) occurs under the rifted margin of the East European craton. The sedimentary cover in this region varies greatly in age and thickness. It is 1–3 km thick beneath the East European craton, 10 km thick the beneath Polish Basin/Lublin trough region, ∼18 km thick in the Carpathian foredeep, and 5–8 km thick beneath the Pannonian Basin. The velocity in the lithospheric mantle is 8.1–8.25 km/s beneath the East European craton, 8.2–8.4 km/s beneath the Variscides–Trans-European suture zone, and 7.8–8.0 km/s beneath Carpathian-Pannonian area. The crust and features in the lithospheric mantle appear to dip northward in this area. In northern Poland, the rifted southwestern margin of the East European craton is abruptly bounded by the Trans-European suture zone and ultimately the Variscides over a region that is only ∼100 km wide, while the collisional zone between the East European craton and the Carpathian-Pannonian area is ∼300 km wide. In both areas, the lithospheric structure observed suggests that the Caledonian, Variscan, and Carpathian orogenies in this area were relatively “soft” collisions that left the East European craton passive margin largely intact. The structural model of the transition between the Pannonian Basin–Carpathians and the East European craton indicates northward “old” subduction under Baltica (Jurassic–Early Cretaceous). However, the thinning of the Pannonian lithosphere could be explained as the result of extension and high heat flow, with “young” southward subduction or slab rollback to the east, which took place in the Tertiary (Miocene).

Potential field data (gravity and magnetic measurements) are both useful and cost-effective tools for many geologic investigations. Significant amounts of these data are traditionally in the public domain. A new magnetic database for North America was released in 2002, and as a result, a cooperative effort between government agencies, industry, and universities to compile an upgraded digital gravity anomaly database, grid, and map for the conterminous United States was initiated and is the subject of this paper. This database is being crafted into a data system that is accessible through a Web portal. This data system features the database, software tools, and convenient access. The Web portal will enhance the quality and quantity of data contributed to the gravity database that will be a shared community resource. The system's totally digital nature ensures that it will be flexible so that it can grow and evolve as new data, processing procedures, and modeling and visualization tools become available. Another goal of this Web-based data system is facilitation of the efforts of researchers and students who wish to collect data from regions currently not represented adequately in the database. The primary goal of upgrading the United States gravity database and this data system is to provide more reliable data that support societal and scientific investigations of national importance. An additional motivation is the international intent to compile an enhanced North American gravity database, which is critical to understanding regional geologic features, the tectonic evolution of the continent, and other issues that cross national boundaries.

With the introduction of many new types of remotely sensed imagery in recent years, opportunities to compare and integrate these data abound. In this paper, we present a hue-saturation-value (HSV) transformation approach for the fusion of surface roughness and shallow subsurface information from Airborne Synthetic Aperture Radar (AIRSAR) data with surface spectral reflectivity from Landsat 7 Enhanced Thematic Mapper Plus (ETM+) data. The fused image is informative and brings out new features that are not evident in the original images, and it also helps to identify many features that are not clear in the original images. In this paper, we also present a combined principal components analysis (CPCA) approach to effectively remove the banding noise that degrades the radar image quality. We examine the differences in surface roughness, texture, and penetration ability at different radar frequencies, the differences between radar and optical (ETM+) images, and the utility of radar images in mapping morphologically defined structures such as fault scarps. The earthquake-related active faults in the Franklin Mountains and Valentine region in West Texas are presented as examples of successful applications of data fusion.

The Trans-European Suture zone in eastern Europe is a complex region that marks the suture of Phanerozoic western European terranes with the Precambrian East European craton. Because of sedimentary cover and the Baltic Sea, the nature of this suture is known primarily from geophysical studies. Seismic velocity and gravity models from earlier experiments indicate changes of crustal thickness from 28–35 km to 42–47 km across the Teisseyre-Tornquist zone from the Paleozoic platform of western Europe to the East European craton. Tectonic models suggest the presence of a Precambrian–early Paleozoic passive margin beneath the Teisseyre-Tornquist zone. The Holy Cross Mountains in southeastern Poland represent an anomalous crustal block whose origin and interaction with the East European craton is unknown. We have employed a new approach to quantitatively integrate (i.e., data fusion) industry-acquired drilling and seismic reflection data, as well as refraction data from the CELEBRATION 2000, POLONAISE ‘97, and Teisseyre-Tornquist zone experiments in a tomographic inversion. We find that it is feasible to integrate data of different resolutions in a tomographic inversion. Secondly, we constrained upper-crustal velocities within our study area to create a more completely resolved velocity structure. Thirdly, we modeled a uniform gravity data set to validate all available data and construct models of crustal structure across the Holy Cross Mountains region.

Geologic and geophysical investigations of the southwestern United States have provided a broad range of noteworthy regional geological and geophysical data sets. These data are integral to understanding the rich and complex geologic history of the region, which has experienced major periods of subduction, uplift, and extension over the past 2 Ga. However, these data are not generally archived in a consistent, digital format that enables interdisciplinary analysis. This paper presents the results of the development of a geographic information system (GIS) of significant geophysical data sets for the Colorado Plateau and southern Basin and Range as part of the SWGEONET project ( http://www.geoinformaticsnetwork.org/swgeonet/ ). The data system contains the following ten compilations: seismic S-wave tomography, receiver functions, shear wave splitting, stress fields, heat flow, thermal conductivity, heat production, complete Bouguer gravity anomaly, geodetic velocity field, and digital elevation models. We utilize the attributes and key findings from these individual data sets in this new infrastructure to better constrain relationships between data sets. To demonstrate the utility of examining these varying data in a common framework, we present four case studies that use GIS tools to join these data sets and provide new views of regional dynamics. These case studies provide estimates of regional variations in crust and/or lithospheric thickness, correlations between independent seismic data sets near the boundaries of the upper mantle transition zone, the potential extent of coupling between the crust and mantle, and possible sources of crustal deformational forces across the region.