Geology Commons^™

Geologic Context Of Geodetic Data Across A Basin And Range Normal Fault, Crescent Valley, Nevada, A. M. Friedrich, Jeffrey Lee, B. P. Wernicke, K. Sieh

All Faculty Scholarship for the College of the Sciences

Geodetic strain and late Quaternary faulting in the Basin and Range province is distributed over a region much wider than historic seismicity, which is localized near the margins of the province. In the relatively aseismic interior, both the magnitude and direction of geodetic strain may be inconsistent with the Holocene faulting record. We document the best example of such a disagreement across the NE striking, ∼55° NW dipping Crescent normal fault, where a NW oriented, 70 km geodetic baseline records contemporary shortening of ∼2 mm/yr orthogonal to the fault trace. In contrast, our geomorphic, paleoseismic, and geochronologic analyses of the …

A Large Late Pleistocene Outburst Flood From Pluvial Lakes Alvord And Coyote Into The Owyhee River, Oregon, Deron Torrey Carter

All Master's Theses

A large late-Pleistocene flood traveled into the Owyhee River as a result of a rise and subsequent outburst from pluvial Lake Alvord in southeastern Oregon. Lake Alvord breached Big Sand Gap after reaching an elevation of 1292 m, releasing 11.3 km3 into the adjacent Coyote Basin before stabilizing at an elevation of about 1280 m. Overflow then spilled out of the Coyote Basin through two outlets at 1278 m and into the Crooked Creek drainage of the Owyhee River. The flood created a series of deeply incised canyons, scabland topography and deposited numerous boulder bars containing imbricated clasts up to …

Energy‐Constrained Open‐System Magmatic Processes 3. Energy‐Constrained Recharge, Assimilation, And Fractional Crystallization (Ec‐Rafc), Frank J. Spera, Wendy A. Bohrson

All Faculty Scholarship for the College of the Sciences

Geochemical data for igneous rock suites provide conclusive evidence for the occurrence of open‐system processes within thermally and compositionally evolving magma bodies. The most significant processes include magma Recharge (with possible enclave formation and magma mixing), Assimilation of anatectic melt derived from wallrock partial melting and formation of cumulates by Fractional Crystallization (RAFC). In this study, we extend the Energetically Constrained Assimilation and Fractional Crystallization (EC‐AFC) model [Spera and Bohrson, 2001; Bohrson and Spera, 2001] to include the addition of compositionally and thermally distinct recharge melt during simultaneous assimilation and fractional crystallization. Energy‐Constrained Recharge, Assimilation, and Fractional …

Seismic Cycle And Rheological Effects On Estimation Of Present-Day Slip Rates For The Agua Blanca And San Miguel-Vallecitos Faults, Northern Baja California, Mexico, Timothy H. Dixon, Julien Decaix, Fred Farina, Kevin Furlong, Rocco Malservisi, Richard Bennett, Francisco Suarez-Vidal, John Fletcher, Jeffrey Lee

All Faculty Scholarship for the College of the Sciences

Geodesy can be used to infer long-term fault slip rates, assuming a model for crust and upper mantle rheology. We examine the sensitivity of fault slip rate estimates to assumed rheology for the Agua Blanca and San Miguel-Vallecitos faults in northern Baja California, Mexico, part of the Pacific–North America plate boundary zone. The Agua Blanca fault is seismically quiet, but offset alluvial fans indicate young activity. Current seismicity is confined to the nearby San Miguel-Vallecitos fault, a small offset fault better aligned with plate motion. GPS measurements between 1993 and 1998 suggest that both faults are active, with a combined …

Whole Mantle Shear Structure Beneath The East Pacific Rise, Timothy I. Melbourne, Donald V. Helmberger

All Faculty Scholarship for the College of the Sciences

We model broadband seismograms containing triplicated S, S², and S³ along with ScS to produce a pure path one‐dimensional model extending from the crust to the core‐mantle boundary beneath the East Pacific Rise. We simultaneously model all body wave shapes and amplitudes, thereby eliminating depth‐velocity ambiguities. The data consist of western North American broadband recordings of East Pacific Rise (EPR) affiliate transform events that form a continuous record section out to 82° and sample nearly the entire East Pacific Rise. The best fitting synthetics contain attenuation and small changes in lithospheric thickness needed to correct for …

Late Quaternary Slip Rates Across The Central Tien Shan, Kyrgyzstan, Central Asia, Stephen C. Thompson, Ray J. Weldon, Charles M. Rubin, Kanatbek Abdrakhmatov, Peter Molnar, Glenn W. Berger

All Faculty Scholarship for the College of the Sciences

Slip rates across active faults and folds show that late Quaternary faulting is distributed across the central Tien Shan, not concentrated at its margins. Nearly every intermontane basin contains Neogene and Quaternary syntectonic strata deformed by Holocene north‐south shortening on thrust or reverse faults. In a region that spans two thirds of the north‐south width of the central Tien Shan, slip rates on eight faults in five basins range from ∼0.1 to ∼3 mm/yr. Fault slip rates are derived from faulted and folded river terraces and from trenches. Radiocarbon, optically stimulated luminescence, and thermoluminescence ages limit ages of terraces and …

Precursory Transient Slip During The 2001 MW = 8.4 Peru Earthquake Sequence From Continuous Gps, Timothy I. Melbourne, Frank H. Webb

Faculty Scholarship for the Cascadia Hazards Institute

Two-hour position estimates from a continuous GPS station located at Arequipa, Peru, document precursory deformation beginning 18 hours prior to an M_w = 7.6 aftershock of the June 23rd 2001 M_w = 8.4 earthquake. This preseismic signal appears on the north and east components as a slow displacement with an amplitude twice that of the subsequent coseismic. Analysis of three years of 18-hour rate measurement shows this signal to be unprecedented and beyond four standard deviations from the mean rate. The best fitting centroid is directionally consistent with slow slip along the plate interface and suggests the preseismic …

Mantle Control Of Plate Boundary Deformation, Timothy I. Melbourne, Don Helmberger

Faculty Scholarship for the Cascadia Hazards Institute

The seismic wavefield propagating along the recently instrumented Pacific-North American plate boundary (California) displays remarkable variation, with regional shear waves arriving at coastal stations up to 20 seconds earlier than equidistant stations in eastern California. Broadband modeling of this data reveals that coastal paths sample fast upper mantle typical of Miocene-aged ocean plate (> 50 Km thickness). Inland paths sample slower uppermost mantle, with the seismic lithosphere, or lid, measuring less than 5 Km thick, characteristic of the Basin and Range extensional province. The boundary in the uppermost mantle between these provinces is sharp, expressing the juxtaposition of the stronger …

Refined Kinematics Of The Eastern California Shear Zone From Gps Observations, 1993-1998, M. Meghan Miller, Timothy H. Dixon, Roy K. Dokka

All Faculty Scholarship for the College of the Sciences

Global Positioning System (GPS) results from networks spanning the Eastern California shear zone and adjacent Sierra Nevada block, occupied annually between 1993 and 1998, constrain plate margin kinematics. We use an elastic block model to relate GPS station velocities to long‐term fault slip rate estimates. The model accounts for elastic strain accumulation on the San Andreas fault, as well as faults of the Eastern California shear zone. South of the Garlock fault, 14 mm/yr of dextral shear is distributed across the Eastern California shear zone. Some of this slip penetrates eastward into the Basin and Range, and a collective budget …

New Kinematic Models For Pacific‐North America Motion From 3 Ma To Present, Ii: Evidence For A “Baja California Shear Zone”, Timothy Dixon, Fred Farina, Charles Demets, Francisco Suarez-Vidal, John Fletcher, Bertha Marquez-Azua, M. Meghan Miller, Osvaldo Sanchez, Paul Umhoefer

All Faculty Scholarship for the College of the Sciences

We use new models for present‐day Pacific‐North America motion to evaluate the tectonics of offshore regions west of the Californias. Vandenburg in coastal Alta California moves at the Pacific plate velocity within uncertainties (∼1 mm/yr) after correcting for strain accumulation on the San Andreas and San Gregorio‐Hosgri faults with a model that includes a viscoelastic lower crust. Modeled and measured velocities at coastal sites in Baja California south of the Agua Blanca fault, a region that most previous models consider Pacific plate, differ by 3–8 mm/yr, with coastal sites moving slower that the Pacific plate. We interpret these discrepancies in …

Evolution Of The Kangmar Dome, Southern Tibet: Structural, Petrologic, And Thermochronologic Constraints, Jeffrey Lee, Bradley R. Hacker, William S. Dinklage, Yu Wang, Phillip Gans, Andrew Calvert, Jinglin Wan, Wenji Chen, Ann E. Blythe, William Mcclelland

All Faculty Scholarship for the College of the Sciences

Structural, thermobarometric, and thermochronologic investigations of the Kangmar Dome, southern Tibet, suggest that both extensional and contractional deformational histories are preserved within the dome. The dome is cored by an orthogneiss which is mantled by staurolite + kyanite zone metasedimentary rocks; metamorphic grade dies out up section and is defined by a series of concentric kyanite-in, staurolite-in, garnet-in, and chloritoid-in isograds. Three major deformational events, two older penetrative events and a younger doming event, are preserved. The oldest event, D1, resulted in approximately E-W trending tight to isoclinal folds of bedding with an associated moderately to steeply north dipping axial …

Present‐Day Motion Of The Sierra Nevada Block And Some Tectonic Implications For The Basin And Range Province, North American Cordillera, Timothy H. Dixon, M. Meghan Miller, Frederic Farina, Hongzhi Wang, Daniel Johnson

All Faculty Scholarship for the College of the Sciences

Global Positioning System (GPS) data from five sites on the stable interior of the Sierra Nevada block are inverted to describe its angular velocity relative to stable North America. The velocity data for the five sites fit the rigid block model with rms misfits of 0.3 mm/yr (north) and 0.8 mm/yr (east), smaller than independently estimated data uncertainty, indicating that the rigid block model is appropriate. The new Euler vector, 17.0°N, 137.3°W, rotation rate 0.28 degrees per million years, predicts that the block is translating to the northwest, nearly parallel to the plate motion direction, at 13–14 mm/yr, faster than …

Surficial Slip Distribution On The Central Emerson Fault During The June 28, 1992, Landers Earthquake, California, Sally F. Mcgill, Charles M. Rubin

All Faculty Scholarship for the College of the Sciences

We present the results of our mapping of a 5.6‐km length of the central Emerson fault that ruptured during the 1992 Landers earthquake in the southwestern Mojave Desert, California. The right‐lateral slip along this portion of the rupture varied from about 150 to 530 cm along the main rupture zone. In some locations a total of up to 110 cm of additional right‐lateral slip occurred on secondary faults up to 1.7 km away from the main rupture zone. Other secondary faults carried up to several tens of centimeters of left‐lateral or thrust displacement. The maximum net vertical displacement was 175 …

Factors Contributing To Landslide Activity In The Winter Of 1995-96, Clearwater County Near Orofino, Idaho, Aaron Paul Wisher

All Master's Theses

Significant landslide activity occurred in Clearwater County, Idaho in November 1995 and February-May 1996. Mass wasting in the study area consisted of debris slides and earthflows triggered by rain-on-snow weather events. It is important to determine what factors contribute to landsliding in this area so that reliable prediction can reduce the destruction of property. Through field observation and aerial photo analysis, the factors contributing to landslides were studied. The objectives included a study of the geology, soils, aspect, slope gradient, vegetation and slope position related to each slide. Also a goal was to assess the role of land use in …

Long Dormancy, Low Slip Rate, And Similar Slip‐Per‐Event For The Emerson Fault, Eastern California Shear Zone, Charles M. Rubin, Kerry Sieh

All Faculty Scholarship for the College of the Sciences

Excavations in a playa along the 1992 rupture of the Emerson fault reveal evidence of two paleoseismic events, with only one large prehistoric rupture in the past 15 millennia. Accelerator mass spectrometer radiocarbon ages of charcoal from playa sediments and from fault‐scarp colluvium directly beneath the playa beds indicate that the last large prehistoric slip event occurred about 9000 ka. Trench‐wall exposures revealed clear evidence of at least one pre‐9 ka rupture at the playa site. The event horizon of this earthquake is between two pedogenic carbonate layers that have radiocarbon ages of 14.8 ka and 24.1 ka, implying that …

The Geodetic Signature Of The M8.0 Oct. 9, 1995, Jalisco Subduction Earthquake, Timothy I. Melbourne, I. Carmichael, C. Demets, K. Hudnut, O. Sanchez, J. Stock, G. Suarez, F. Webb

Faculty Scholarship for the Cascadia Hazards Institute

The October, 1995 Mw 8.0 Jalisco subduction earthquake has provided a thorough geodetic observation of the coseismic subduction process. An 11 station regional GPS network located directly onshore of the rupture demonstrates consistent vertical subsidence verified by tide gauge data and southwest-directed extension, with measured displacements reaching 1 meter. Unusually shallow and non-uniform faulting is required to explain the displacements. We determine that up to 5 meters of slip occurred within the upper 15 km of the thrust fault zone and 2 meters possibly as shallow as 8 km, and that slip was likely distributed in two main patches. The …

Prolonged History Of Silicic Peralkaline Volcanism In The Eastern Pacific Ocean, Wendy A. Bohrson, Mary R. Reid, Anita L. Grunder, Matthew Heizler, T. Mark Harrison, Jeffrey Lee

All Faculty Scholarship for the College of the Sciences

Socorro Island, Mexico, is an alkaline and peralkaline volcanic island located in the eastern Pacific Ocean on a mid-ocean ridge spreading center that was abandoned at ∼3.5 Ma. Silicic peralkaline rocks comprise up to 80% of the surface of the island, rendering Socorro virtually unique in the Pacific Ocean. Precise, replicate ⁴⁰Ar/³⁹Ar ages of 21 peralkaline trachytes and rhyolites reveal a history of episodic volcanic activity from ∼540 to 370 ka that may have culminated with caldera formation; repose periods between these episodes may have had maximum duration of ∼30 kyr. After up to 200 kyr of …

Constraints On Present-Day Basin And Range Deformation From Space Geodesy, Jeffrey Lee, Timothy H. Dixon, Stefano Robaudo, Marith C. Reheis

All Faculty Scholarship for the College of the Sciences

We use new space geodetic data from very long baseline interferometry and satellite laser ranging combined with other geodetic and geologic data to study contemporary deformation in the Basin and Range province of the western United States. Northwest motion of the central Sierra Nevada block relative to stable North America, a measure of integrated Basin and Range deformation, is 12.1±1.2 mm/yr oriented N38°W±5° (one standard error), in agreement with previous geological estimates within uncertainties. This velocity reflects both east-west extension concentrated in the eastern Basin and Range and north-northwest directed right lateral shear concentrated in the western Basin and Range. …

Rapid Uplift And Rotation Of Mylonitic Rocks From Beneath A Detachment Fault: Insights From Potassium Feldspar 40ar/39ar Thermochronology, Northern Snake Range, Nevada, Jeffrey Lee

All Faculty Scholarship for the College of the Sciences

The thermal histories of mylonitic rocks from the footwall of the northern Snake Range decollement (NSRD), Nevada, were calculated using multiple diffusion domain analyses of potassium feldspar Arrhenius data and ⁴⁰Ar/³⁹Ar age spectra in order to characterize the cooling (exhumation) history of these mylonitic rocks and thereby constrain the origin and movement history of the NSRD. The calculated thermal histories, along with reported apatite fission track ages, indicate the three following episodes of rapid cooling (10–55°C/m.y.) related to extensional denudation: (1) middle Eocene (48–41 Ma), (2) late Oligocene (30–26 Ma), and (3) early Miocene (20–16 Ma). The …

Do Microplates In Subduction Zones Leave A Geological Record?, Jeffrey Lee, Joann M. Stock

All Faculty Scholarship for the College of the Sciences

Active microplate boundaries in ocean-continent subduction zones may induce deformation of the overlying plate and spatial or geochemical variations in the volcanic arc. We discuss two modern cases. The first is the South Gorda-Juan de Fuca plate boundary in the Cascadia subduction zone, where there is little or no effect on the overriding plate and the oceanic plate takes up much of the deformation. The second case is the Cocos-Rivera plate boundary in the Middle America trench, where the overlying Colima graben contains substantial deformation in a zone extending from the trench to the volcanic arc and the sub-duction-related volcanism …

Life History Of The Ginko Petrified Forest Or The Autobiography Of An Ancient Oak Tree, George F. Beck

Geological Sciences Faculty Scholarship

An account of a fossilized log at Ginkgo Tree State Park written by the man who discovered the fossil trees and established there were Ginkgo trees in North America in the distant past.

The booklet is written from the perspective of one of the fossilized trees, tracing the geologic forces that led to it becoming a fossil.

Additions To The Late Tertiary Floras Of The Pacific Northwest, George F. Beck

All Faculty Scholarship for the College of the Sciences

The purpose of this paper and those which will follow, is to present new types of flora found in several older leaf localities of the Pacific Northwest. A study will also be made of a number of new localities as yet not reported upon in the literature. The present paper refers to several new species found at the Bull Quarry, Ellensburg, and the Brickyard locality, Spokane, Washington. Both sites have been studied and reported upon in the past, as noted in attached bibliography.

Washington Petrified Forests-Ginkgo Exotic Forest, George F. Beck

All Faculty Scholarship for the College of the Sciences

Seven years ago we began our study of the Ginkgo Petrified Forest in Central Washington. This is in reality a series of forests occurring at various horizons in the Yakima ( and Wenas?) basalts throughout a vertical range of some 2,000 feet, and in a belt 150 miles long, and 50 miles wide, centering at Vantage on the Columbia River.

Determination Of Fossil Woods (Basswood In Ellensburg Formation), George F. Beck

All Faculty Scholarship for the College of the Sciences

From time to time isolated, rounded pebbles of petrified wood have been encountered in the Ellensburg gravels that overlie the Columbia Basalts in Central Washington. Recently a sufficient number of these specimens were collected to justify a study of the petrified woods of this above-named formation.

Determining Fossil Woods (Western Conifers), George F. Beck

All Faculty Scholarship for the College of the Sciences

In this paper we come to consider the problem of the coniferous woods. One cannot always recognize with certainty that a given wood is a conifer, yet in ninety percent of the specimens recognition is simple.

Remarkable West American Fossil, The Blue Lake Rhino, George F. Beck

All Faculty Scholarship for the College of the Sciences

Bidding for acceptance as fact, and for its place in the sun of fame and notoriety, we come now to the newly discovered fossil rhino animal mold of Blue Lake in Grand Coulee, central Washington. Not that fossil rhinos are rare or that their abundance in the Tertiary of America has waited until the present for revelation, is this fossil important. The feature in the Blue Lake rhino which taxes our credulity is the existence of the thing in what unquestionably must pass as once liquid basaltic lava. That anything organic could pass through the terrific heat and pressure of …

Determination Of Fossil Woods (Part V-Beech-Sycamore-Alder), George F. Beck

All Faculty Scholarship for the College of the Sciences

The group of woods considered in this paper are only superficially alike—no implication that they are closely related is intended. The beginner will almost certainly confuse the compound rays of these various woods with their annual rings.

Formations Of The Columbia Basin, Parade Of Extinct Mammals, George F. Beck

All Faculty Scholarship for the College of the Sciences

In this preliminary chart are shown the extinct mammals encountered as fossils in the various formations among and above the great Columbia Basalt series of the Pacific Northwest. A few shown as appearing in the Lake Vantage horizon of the basalts.

Determination Of Fossil Woods (Part Iv-Walnut-Hickory-Persimmon), George F. Beck

All Faculty Scholarship for the College of the Sciences

These three woods undoubtedly ranged over Western America in Tertiary and were well represented in the Ginkgo series of forest during Miocene. Fossil walnut wood is the more abundant of the three species, while hickory is not common.

Camels Of The Columbia Plateau, George F. Beck

All Faculty Scholarship for the College of the Sciences

However foreign they may seem to us the camels are one of our oldest American stocks. Our Western plains once supported large herds of them, humped and humpless, large and small, giraffe-necked and normal-necked. For some 35 million years, from Oligocene to the Pliocene, the camels were confined to North America and it was not until recently, geologically speaking that we shared the race with the Old World.