Doyle R. Watts

Preliminary conclusions of the Royal Society and Academia Sinica 1985 geotraverse of Tibet

The 1985 Chinese/British expedition to the Tibetan Plateau attempted to solve the question of the origin of the very thick crustal rocks in this region. Continuing northwards movement of the Indian plate over the past 38 Myr has given rise to severe folding and thrust faulting, causing crustal thickening by internal deformation. Previous collisions of microplate terranes derived from Gondwanaland occurred during Mesozoic times but the Kun Lun terrane of northern Tibet was already part of Laurasia by the Carboniferous.

Ground-roll suppression using the wavelet transform

Low‐frequency, high‐amplitude ground roll is an old problem in land‐based seismic field records. Current processing techniques aimed at ground‐roll suppression, such as frequency filtering, f-k filtering, and f-k filtering with time‐offset windowing, use the Fourier transform, a technique that assumes that the basic seismic signal is stationary. A new alternative to the Fourier transform is the wavelet transform, which decomposes a function using basis functions that, unlike the Fourier transform, have finite extent in both frequency and time. Application of a filter based on the wavelet transform to land seismic shot records suppresses ground roll in a time‐frequency sense; unlike the Fourier filter, this filter does not assume that the signal is stationary. The wavelet transform technique also allows more effective time‐frequency analysis and filtering than current processing techniques and can be implemented using an algorithm as computationally efficient as the fast Fourier transform. This new filteri...

Mapping granite and gneiss in domes along the North Himalayan antiform with ASTER SWIR band ratios

A series of five gneiss domes that are exposed along the axis of the North Himalayan antiform 50 km south of the Indus-Tsangpo suture, southern Tibet, are characterized by cores of Cambrian gneiss and Neoproterozoic-Paleozoic schists and migmatites, often intruded by Tertiary granites and mantled by metamorphosed equivalents of Tethyan sedimentary successions. Images from the SWIR (short wave infrared) bands recorded by the ASTER (Advanced Spaceborn Thermal Emission and Reflection Radiometer) sensor on the Earth Observation System Terra satellite reveal with unprecedented clarity the nature of the cores of the domes and the extent of the surrounding mantles of metamorphic rock. Using band ratio methods, we distinguish Tertiary granite from Cambrian gneiss on the basis of the presence of 5%–10% muscovite in the granite. This methodology is ideally suited to the mapping of a relatively inaccessible area with excellent exposure but limited ground truth. With the exception of the well-studied Kangmar dome, our images of the cores of the domes and their associated mantles bear little resemblance to the published geological maps of the region and reveal hitherto unrecognized exposures of granites. The true disposition of the domes within the North Himalayan antiform have now been established, revealing a systematic westward increase in the granite component of Himalayan age within the domes across the study area.

Identifying Gypsy Moth Defoliation in Ohio Using Landsat Data

The gypsy moth is one of the most devastating forest pests in North America. The Ohio Department of Agriculture, in common with other state agencies involved in the Gypsy Moth Suppression Program, uses aerial sketch mapping each year to map gypsy moth damage. We compare results obtained from Landsat 5 and Landsat 7 to locations determined by aerial sketch mapping to locate gypsy moth infestations in Ohio. The haze-corrected ratio of Landsat band 4 (near infrared) to band 3 (red) detects changes of leaf area. We subtract the ratio values from two dates to determine the change. As in previous studies, we search for the defoliation caused by the gypsy moth by subtracting the ratio values of frames acquired in early June and late June. Unlike previous studies, we use the subsequent refoliation that takes place between late June and late July as part of the signal. This is seen as large positive ratio subtraction values between early June and late June and large negative ratio subtraction values between late June and late July. Pixels that exhibit these attributes are candidates for gypsy moth defoliation. The use of three frames to analyze both defoliation and subsequent refoliation results in a stronger, less ambiguous signal of gypsy moth damage and pinpoints the locations of the most severe defoliation. The most severe defoliation often marks the location of egg masses. Although we reduced the ambiguity caused by agricultural anomalies, this procedure also detected areas with significant wild grapevine infestations.

Terrain correction program for regional gravity surveys

An algorithm is presented for the computation of gravity terrain corrections from a digitized grid representing topography. Different approximations for topography at various distances from the gravity station are used to make the computation more efficient. For the distant zone (30 < r < 50 km) topography is approximated using a vertical line mass distribution. In the intermediate zone (2 < r < 30 km) a segment of a hollow vertical cylinder is used. The near zone (0.5 < r < 2 km) is approximated using vertical rectangular prisms with sloping upper faces. A new method is used to compute the correction for the inner zone which is the digitized square where the gravity station is located. The gravity effect of topography in the inner zone is calculated from four traingular prisms with vertices made of the station location and the corners of the square. The computer program has been tested comprehensively with a regional gravity database from the Southern Uplands of Scotland in which all terrain corrections were carried out originally using the Hammer chart method.

High-resolution images of the lower crust: deep seismic reflections from 15 to 180 Hz

Abstract We report the results of an unconventional, broad-band deep-seismic reflection survey undertaken on land in southwest England. Previous marine seismic lines in this area have shown strong layered lower-crustal reflectivity. The broad-band survey shows near-normal-incidence P-wave reflections from the lower continental crust and from the Moho with frequencies that range from 15 to 180 Hz. High-frequency lower-crustal S-wave reflections were also observed. These high frequencies were obtained by placing both sources and receivers in boreholes up to 2 km deep, drilled within a large homogeneous granite pluton. Recording down-hole avoids loss of high frequency energy during transmission through heterogeneous and highly attenuative near-surface layers. The high frequencies were generated using explosive sources, and were recorded on sub-surface accelerometers and hydrophones, and on a conventional array of surface geophones. Seismic attenuation within the granite is low; the quality factor, Q , lies above 2000. These new, high-frequency observations show that the lower crust does not preferentially reflect particular frequencies. The data are most readily explained as resulting from the combination of a frequency-independent Q in the upper crust with a white reflectivity response in the lower crust. The data are not consistent with crustal models which are highly tuned to reflect preferentially the frequencies employed in conventional deep seismic reflection surveys. The data require relatively sharp boundaries within the lower crust; significant variation in physical properties must occur over vertical distances of not more than about 10 m. Sharp boundaries are most easily explained if the reflections result from lithological contrasts.

Scintillometer-Based Estimates of Sensible Heat Flux Using Lidar-Derived Surface Roughness

AbstractThe estimation of sensible heat flux, H, using large aperture scintillometer (LAS) under varying surface heterogeneity conditions was investigated. Surface roughness features characterized by variable topography and vegetation height were represented using data derived from the highly accurate light detection and range (lidar) techniques as well as from traditional vegetation survey and topographic map methods. The study was conducted at the Cibola National Wildlife Refuge, Southern California, over a riparian zone covered with natural vegetation dominated by tamarisk trees interspersed with bare soil in a region characterized by arid to semiarid climatic conditions. Estimates of H were obtained using different representations of surface roughness features derived from both traditional and lidar methods to estimate LAS beam height [z(u)] at each increment u along its path, vegetation height (hc), displacement height (d), and roughness length (z0) combined with the LAS weighing function, W(u), alon...

An ancient river channel system incised on the Precambrian–Cambrian unconformity beneath Jackson County, Ohio

We analyzed a migrated three-dimensional (3-D) seismic reflection data set collected from Jackson County, Ohio, using volume-based voxel visualization technology. Adjusting the opacities of voxels in a time slab centered on the Precambrian reflector revealed a drainage channel system incised on the Ohio Precambrian surface, approximately 1460 m (4800 ft) below sea level. Formation sculpting of the Precambrian surface produced an image of 100-m (330-ft)-wide tributaries on the Precambrian unconformity joining to produce a 400-m (1320-ft)-wide channel roughly parallel to the subsurface trend of the Grenville front beneath Ohio. Broadening and splitting of the zero-phase seismic wavelet that defines the Precambrian reflector reveals the channels. The seismic signature is caused by thin-bed interference effects caused by reflections at the boundary between the channel fill with the overlying Mount Simon Formation and the boundary with the underlying Precambrian surface. The seismic images, therefore, locate a new lithologic unit in the Ohio subsurface. The channels are older than the overlying Mount Simon Formation and so must be at of least Middle Cambrian age. The channel morphology indicates flow in the direction of the Rome trough, approximately 60 km (37 mi) to the south, likely transporting sediment to that basin. Given the tiny volume of Ohio sampled by 3-D seismic methods, such buried channels must be common on the Precambrian surface.

Separation and enhancement of split S‐waves on multicomponent shot records from the BIRPS WISPA experiment

Instantaneous rotations are combined with f-k filtering to extract coherent S‐wave events from multicomponent shot records recorded by British Institutions Reflection Profiling Syndicate (BIRPS) Weardale Integrated S‐wave and P‐wave analysis (WISPA) experiment. This experiment was an attempt to measure the Poisson’s ratio of the lower crest by measuring P‐wave and S‐wave velocities. The multihole explosive source technique did generate S‐waves although not of opposite polarization. Attempts to produce stacks of the S‐wave data are unsuccessful because S‐wave splitting in the near surface produced random polarizations from receiver group to receiver group. The delay between the split wavelets varies but is commonly between 20 to 40 ms for 10 Hz wavelets. Dix hyperbola are produced on shot records after instantaneous rotations are followed by f-k filtering. To extract the instantaneous polarization, the traces are shifted back by the length of a moving window over which the calculation is performed. The ins...

Deep gas well encounters ultramafic kimberlite-like material in the Sauk Sequence of southeastern Ohio, USA

The first indication of a potential deep-subsurface kimberlite-like material in the Appalachian Basin, without surface expression, has been discovered in oil and gas well drilling samples from a deep well drilled near Zanesville, Ohio, USA. The well was drilled into the Cambrian Sauk Sequence within a localized fault-bounded graben, where a zone of ultramafic rocks was encountered. The zone of ultramafic rocks is within Sauk carbonates at 1720 m below sea level and is not highly anomalous on geophysical wire-line well logs. Petrographic analyses of grain-mounted samples show a 20 m zone of ultramafic rock material near the top of the Conasauga Group. Well cuttings from the ultramafic zone include relatively fresh phenocrysts of phlogopite with calcite, apatite, and titaniferous magnetite, in a secondary matrix of amphibole, chlorite, Fe-oxides, and possibly serpentine. The rocks have undergone deuteric alteration and probably later hydrothermal alteration. A 20-m-thick, localized, natural gas–bearing sandstone unconformably overlies (Knox unconformity) the Sauk Sequence above the ultramafic zone. Structural mapping indicates that the localized sandstone is confined to a small seismic-defined graben originating in the faulted Precambrian Grenville basement complex. Mapping of newly acquired gravity and magnetic data does not indicate the presence of an anomaly coincident with the graben, suggesting that the ultramafic material must be a very small, localized intrusive body (pipe or diatreme). Alternative interpretations include a thin intrusive sill, extrusive tuff deposits, Grenville-aged tectonic fault slice, or eroded igneous deposits. Subsurface mapping of units above the Sauk Sequence (Ordovician Black River Group–Trenton Limestone) shows no significant variation in structural contours above the feature. Although the igneous material has not been isotopically dated, the stratigraphic position suggests that it was intruded prior to Middle Ordovician time.