Jose Manuel Ramirez Hurtado

Southward extrusion of Tibetan crust and its effect on Himalayan tectonics

The Tibetan Plateau is a storehouse of excess gravitational potential energy accumulated through crustal thickening during India-Asia collision, and the contrast in potential energy between the Plateau and its surroundings strongly influences the modern tectonics of south Asia. The distribution of potential energy anomalies across the region, derived from geopotential models, indicates that the Himalayan front is the optimal location for focused dissipation of excess energy stored in the Plateau. The modern pattern of deformation and erosion in the Himalaya provides an efficient mechanism for such dissipation, and a review of the Neogene geological evolution of southern Tibet and the Himalaya shows that this mechanism has been operational for at least the past 20 million years. This persistence of deformational and erosional style suggests to us that orogens, like other complex systems, can evolve toward “steady state” configurations maintained by the continuous flow of energy. The capacity of erogenic systems to self-organize into temporally persistent structural and erosional patterns suggests that the tectonic history of a mountain range may depend on local energetics as much as it does on far-field plate interactions.

Neotectonics of the Thakkhola graben and implications for recent activity on the South Tibetan fault system in the central Nepal Himalaya

The Thakkhola graben is one of many north-trending rifts that define the Neogene structural pattern of the southern Tibetan Plateau. Lying at the southern margin of the plateau and extending to the crest of the Himalaya, the graben provides an opportunity to evaluate the kinematic relationships between east-west extensional strain in southern Tibet and north-south extensional strain in the Himalaya. Neotectonic and structural mapping of the Dangardzong fault along the western margin of the graben reveals a southward-decreasing component of normal slip coupled with a southward-increasing component of right-lateral slip that affects Pleistocene basin-fill sediments. We present 14C ages for river terraces in the Thakkhola graben that provide a ca. 17.2 ka minimum age on the latest stage of Dangardzong fault movement. Near the southern termination of the graben, the Dangardzong fault apparently offsets the Annapurna detachment, an early (Miocene) strand of the east-striking South Tibetan fault system. However, the Dangardzong fault itself terminates against a young (i.e., younger than ca. 17.2 ka) strand of the South Tibetan fault system, the Dhumpu detachment. Structural relationships among the Dangardzong, Annapurna, and Dhumpu faults suggest that the Dangardzong structure is a tear fault in the South Tibetan allochthon that accommodates differential amounts and rates of displacement along the South Tibetan fault system. Thus, although the South Tibetan fault system first developed as part of the structural architecture of the Himalaya in Miocene time, at least some strands have been active as recently as the Pleistocene. In a regional context, the South Tibetan fault system serves to accommodate the strain gradient between extension in Tibet and shortening in the Himalaya.

Computer-based data acquisition and visualization systems in field geology: Results from 12 years of experimentation and future potential

Paper-based geologic mapping is now archaic, and it is essential that geologists transition out of paper-based fi eld work and embrace new fi eld geographic information system (GIS) technology. Based on ~12 yr of experience with using handheld computers and a variety of fi eld GIS software, we have developed a working model for using fi eld GIS systems. Currently this system uses software products from ESRI (Environmental Systems Research Institute, Inc.) (ArcGIS and ArcPad), but the data model could be applied to any GIS system. This fi eld data model is aimed at simultaneously increasing the effi ciency of fi work while adding the attributing capability of GIS to develop fi eld data products that are more data rich than any paper map could ever achieve. We emphasize three basic rules in the development of this data structure. (1) A fi eld GIS map should emphasize line and point objects, avoiding polygons, objects that can easily be constructed outside of the fi eld environment. (2) Keep it simple stupid (KISS) is a critical rule for setting up data structures to avoid fi eld GIS systems that are less effi cient than paper. (3) Data structures need to develop a compromise between display and data entry, with display always trumping data entry because geologic insight is the primary goal. This paper contains two sample blank databases that illustrate these approaches for two applications: (1) generic bedrock geologic mapping, and (2) metamorphic geology mapping multiple generations of fabrics. Key features in our approach are to use display as a fi rst-order attribute, sorting point objects into four basic types (station, orientation, sample, photo) and lines into the four basic contact types (depositional contact, unconformity, intrusive contact, fault), plus other specialized data layers where needed. Individual GIS objects are further attributed, but attributing is limited to critical information with all objects carrying a special “note” fi eld for input of nonstandard information. We suggest that when fi eld GIS systems become the norm, fi eld geology should enjoy a revolution both in the attitude of the fi eld geologist toward his or her data and the ability to address problems using the fi eld information. However, fi eld geologists will need to adjust to the changing technology, and many longestablished fi eld paradigms should be reevaluated. One example is the rule that all linework on geologic maps needs to be perfected in the fi eld setting. Our experience suggests that with modern high-resolution imagery (aerial photography and topographic shaded reliefs) and digital elevation models, fi eld work should evolve into an iterative process where map linework is roughed out in the fi eld, refi ned during evening fi eld sessions, then potentially revisited if problems arise. This procedure is particularly effi cient when three-dimensional visualization is added to the system, a feature that will soon become the norm rather than the exception. We note that using these systems is particularly important for future developments in metamorphic geology, sedimentary geology, and astrogeology, but other applications are clearly also possible. For geoscience instructors who teach fi eld geology classes, we note that it is critical that these systems be incorporated into all geoscience fi eld programs, but research is needed on the best teaching approaches in the use of the technology.

Images with Uncertainty: Efficient Algorithms for Shift, Rotation, Scaling, and Registration, and Their Applications to Geosciences

• different images bring different information; so, to get a better understanding, we must fuse the corresponding data; e.g., we must combine a satellite images with a radar image; • comparison of two images – e.g., images made at different moments of time – can also give us information about the changes: e.g., by comparing preand post-earthquake images, we can determine the effect of the earthquake.

Slip analysis of the Kokoxili earthquake using terrain-change detection and regional earthquake data

The Kokoxili earthquake occurred on 14 November 2001 along the Kunlun fault. To analyze the type of deformation along several segments of the fault, this study employs Fourier transform terrain-change detection to detect horizontal pixel offsets between time-separated Advanced Spaceborne Thermal Emission and Refl ection Radiometer (ASTER) satellite images. The results allow us to model the slip direction and amount of slip due to the earthquake. Three segments of the fault were analyzed, each with different strain kinematics. Our analysis detected left-lateral slip, a displacement of 311 m, and areas of transpression and transtension in the proximal area of the Kunlun fault. The image geodetic results are consistent with published fi eld measurements and stress analysis using regional earthquake data. The combination of the fi eld measurements, stress and strain analysis, and geodetic results displays patterns of deformation along the fault that are infl uenced by the fault’s geometry. This study demonstrates for the fi rst time the utility of ASTER optical satellite imagery for acquiring quantitative measurements of surface deformation.