Bells Canyon - Utah Geological Survey

More documents

Recommendations

Info

6show that the surface faulting at Coyote Gulch did notextend north to the Middleton site, indicating the likelypresence of a previously unrecognized rupture segmentboundary between the two sites. Based on the geometryof the fault, we believe the boundary is at a pronouncedright bend in the fault just north of Coyote Gulch. Wehave named the proposed new northern segment theCedar City segment.Developing Long-Term Fault-Slip Data from DisplacedBasalt FlowsFault slip rates (net fault displacement divided by time)allow us to study the behavior of faults over several earthquakecycles. The higher the slip rate, the more active andpotentially hazardous is the fault. Where it is possible todetermine slip rates for a variety of time intervals, we canevaluate changes in the fault’s behavior through time.Knowing if a fault is slowing down or speeding up isimportant when evaluating earthquake hazards. The Hurricanefault provides a rare opportunity to develop longtermslip rates from displaced basalt flows along its length.We used detailed geochemical data to correlate the displacedflows, and paleomagnetic data and new geologicmapping to evaluate the extent of near-fault deformationadjacent to the fault. We then calculated the net slip acrossthe fault, and dated the correlated basalts to determine thetime period over which the slip occurred.We identified four locations in Utah where displacedbasalts can be correlated across the Hurricane fault (seetable below). We also identified a fifth site east of CedarCity in Cedar Canyon where a basalt flow occupies theancestral channel of Coal Creek high on the north wall ofthe canyon. When the basalt flowed down the channel ofCoal Creek, it forced the stream to find a new path. CoalCreek has since re-established its channel and left thebasalt stranded high above the present stream. BecauseCoal Creek is graded to Cedar Valley and crosses the Hurricanefault at the mouth of Cedar Canyon, movement onthe fault controls the base level of the stream and thestream incision rate. Therefore, the rate of stream incisionis a proxy for slip on the fault. The following table showsthe net slip across the fault at each of the five basalt locations,the ages of the correlated basalts, and the resultingslip rate.Location Net Slip Basalt Age Slip Rate(meters) (million years) (mm/yr)Grass Valley 440 1.0 0.44Pah Tempe 73 0.353 0.21S. Black Ridge 368 0.81 0.45N. Black Ridge 476 0.86 0.55Cedar Canyon 335 0.63 0.53Long-term slip rates developed from displaced Quaternarybasalt flows in Utah.S URVEY N OTESLooking southeast at the Shurtz Creek fault scarp where theUGS attempted to trench the Hurricane fault. The scarp isabout 40 feet high.The Hurricane Cliffs looking northwest from near the Utah/Arizonaborder. The Hurricane fault is at the base of the cliffs; stratigraphicdisplacement across the fault is more than 2,000 feet.The table and figure show that slip on the Hurricane faultincreases from south to north. Additionally, although thedata are sparse, slip rates appear to increase incrementallyacross a suspected segment boundary at South BlackRidge, lending credence to the idea that a seismogenicboundary exists at that location. Although little change inlong-term slip rate is apparent north of South Black Ridge,slip rates determined for segmented faults elsewhere inthe western United States indicate that a seismogenicboundary could still be present between the proposed AshCreek and Cedar City segments.STUDY CONCLUSIONSResults of this study show that the Hurricane fault in Utahlikely consists of three rupture segments, rather than twoas previously thought. The newly proposed segment atthe north end of the fault has been named the Cedar Citysegment. Of the three segments, the Cedar City segmenthas gone the longest without a surface-faulting earthquake.The single slip rate available for the new CedarCity segment closely approaches that of the Ash Creeksegment to the south, which has had a surface-faultingearthquake in recent geologic time. Therefore, given itshigh long-term record of activity and because it has gonethe longest without a surface-faulting earthquake, theCedar City segment is considered the most likely locationfor a large earthquake on the Hurricane fault in Utah.
S URVEY N OTES 7Energy NewsGEOTHERMAL RESOURCES OF UTAH-2001A Digital Atlas for Utah’s Geothermal Resourcesby Robert E. Blackett and Sharon I. WakefieldIn response to increasing interest innational renewable energy sources,the Utah Geological Survey (UGS), incooperation with the Utah EnergyOffice, is completing work on a new,interactive, digital publication basedupon geographic information system(GIS) technology. Geothermal Resourcesof Utah-2001, which will be publishedon compact disk (CD), contains datafrom publicly available reports anddata sets available through 2000. TheCD contains technical information forscientists and engineers, but its interactive,menu-driven reports, tables,and maps make it suitable for generalpublic use.The CD replaces a geothermalresource map of the state of Utah producedas part of a U.S. Department ofEnergy/UGS cooperative geothermalprogram in the late 1970s. Publishedin 1980, the Geothermal Resources ofUtah map presented geothermal andwater-resource data at a scale of1:500,000. Although the informationpresented on the map was of a generalnature, it showed locations of thermalwells and springs and listed individualsource temperatures, waterqualitydata, and flow rates. The mapalso outlined areas of prospectivevalue for geothermal resources, andprovided descriptive informationabout individual geothermal areas. Itwas published through the U.S.National Oceanic and AtmosphericAdministration and is now out ofprint.The 1980 map needs replacingbecause it is out of date and availableonly in a few libraries, at a time wheninterest in renewable energy resourcesand technology is increasing. Sincepublication of the 1980 map, variousworkers completed a number of geothermal-relatedstudies, the result offederal, state, and privately fundedresearch. In addition to regional andstatewide resource assessments, thestudies also involve detailed analysesof individual geothermal areas. Inclusionof the data from these studiesmakes the new CD superior to the1980 map.The CD will contain (1) Adobe Acrobat®portable document format (PDF)documents describing geothermalresources of Utah and specific geothermalareas; (2) digital PDF maps ofUtah and individual geothermalareas; (3) a 3,000-record database ofthermal wells and springs; (4) geothermal,geologic, geographic, cultural,and infrastructure-related spatialdata (ArcView®) files; (5) documentationand description of data sourcesand accuracy (metadata); (6) imagefiles; and (7) software (ArcExplorer®)to construct and view various GISthemes, maps, images, and reports.Readers of Survey Notes may refer tothe article and map in vol. 32, no. 3 tonote some of the complexity.The PDF documents, spatial data,metadata, image files, and softwareare organized into six subfolders:Docs: PDF documents containingreports on geothermal resourcesand heat flow in Utah, data tablesof thermal wells and springs, acomprehensive geothermal bibliographyof Utah, and user guidesfor the CD and the freeware.Geoth_db: A database containing nearly3,000 records of thermal wellsand springs in Utah.Images: GIS-generated geothermalmaps of Utah (PDF) and photos ofUtah geothermal sites.Menu: Applications for driving theCD-ROM menu system.Shapes: Spatial data layers (asArcView® shapefiles) containingbase maps and infrastructuredata, as well as updated geothermalwell and spring data andheat-flow data for Utah. Metadatafiles that document the GIS layersare also included.Software: ArcExplorer® and AdobeAcrobat® Reader freeware. Arc-Explorer® enables users toretrieve and manipulate a varietyof maps using the ArcView®shapefiles. Adobe Acrobat®Reader allows users to view PDFdocuments.With the documents, databases, andsoftware on the CD, users will be ableto create individual GIS maps at varyingscales containing any number ofdata layers. Data layers could includegeothermal resources, land use, cultural,demographic, land grid, geologic,geographic, infrastructure, andother information as needed. GISusers can also import new or updateddata layers from the Utah AutomatedGeographical Reference Center website(http://agrc.its.state.ut.us/) andelsewhere.The Geothermal Resources of Utah-2001 CD is scheduled for publicationnear the end of 2001 and will be availablethrough the Utah Department ofNatural Resources Bookstore.
Page 1 and 2: U T A H G E O L O G I C A L S U R V
Page 3 and 4: S URVEY N OTES 1New Mapping of Eart
Page 5 and 6: S URVEY N OTES 3Contorted beds are
Page 7: S URVEY N OTES 5Investigating Past
Page 11 and 12: S URVEY N OTES 9GEOLOGYTeacher’s
Page 13 and 14: S URVEY N OTES 11GeoSightsby Carl E
Page 15 and 16: S URVEY N OTES 13came from? Or what

Bells Canyon - Utah Geological Survey

Create successful ePaper yourself

Delete template?

Save as template?