Geophysics and Seismology Commons^™

Size And Exhumation Rate Of Ultrahigh-Pressure Terranes Linked To Orogenic Stage, Andrew R.C. Kylander-Clark, Bradley R. Hacker, Chris G. Mattinson

All Faculty Scholarship for the College of the Sciences

A growing set of data indicates a stark contrast between the evolution of two types of ultrahigh-pressure (UHP) terranes: large terranes that evolved slowly (over 10–30 Myr), and small terranes that formed and were exhumed on timescales of < 10 Myr. Here we compare the characteristics – area, thickness, formation rate, exhumation rate, age, and tectonic setting – of these two endmember types of UHP terrane worldwide. We suggest that the two UHP terrane types may form during different orogenic stages because of variations in the buoyancy and traction forces due to different proportions of subducting crust and mantle lithosphere or to different rates of subduction. The initial stages of continent collision involve the subduction of thin continental crust or microcontinents, and thus tectonic forces are dominated by the density of the oceanic slab; subduction rates are rapid and subduction angles are initially steep. However, as collision matures, thicker and larger pieces of continental material are subducted, and the positive buoyancy of the down-going slab becomes more prominent; subduction angles become gentle and convergence slows. Assessing the validity of this hypothesis is critical to understanding the physical and chemical evolution of Earth's crust and mantle.

Included here is the post-print copy of this article. The final publication is available via ScienceDirect at http://www.sciencedirect.com/science/article/pii/S0012821X11007564

Stratigraphic Record Of Holocene Coseismic Subsidence, Padang, West Sumatra, Tina Dura, Charles M. Rubin, Harvey M. Kelsey, Benjamin P. Horton, Andrea Hawkes, Christopher H. Vane, Mudrik Daryono, Candace Grand Pre, Tyler Landinsky, Sarah Bradley

All Faculty Scholarship for the College of the Sciences

Stratigraphic evidence is found for two coseismic subsidence events that underlie a floodplain 20 km south of Padang, West Sumatra along the Mentawai segment (0.5°S–0.3°S) of the Sunda subduction zone. Each earthquake is marked by a sharp soil‐mud contact that represents a sudden change from mangrove to tidal flat. The earthquakes occurred about 4000 and 3000 cal years B.P. based on radiocarbon ages of detrital plant fragments and seeds. The absence of younger paleoseismic evidence suggests that late Holocene relative sea level fall left the floodplain too high for an earthquake to lower it into the intertidal zone. Our results …

Recent Increase In Black Carbon Concentrations From A Mt. Everest Ice Core Spanning 1860-2000 Ad, Susan D. Kaspari, M. Schwikowski, M. Gysel, M. G. Flanner, S. Kang, S. Hou, P. A. Mayewski

All Faculty Scholarship for the College of the Sciences

A Mt. Everest ice core spanning 1860–2000 AD and analyzed at high resolution for black carbon (BC) using a Single Particle Soot Photometer (SP2) demonstrates strong seasonality, with peak concentrations during the winter‐spring, and low concentrations during the summer monsoon season. BC concentrations from 1975–2000 relative to 1860–1975 have increased approximately threefold, indicating that BC from anthropogenic sources is being transported to high elevation regions of the Himalaya. The timing of the increase in BC is consistent with BC emission inventory data from South Asia and the Middle East, however since 1990 the ice core BC record does not indicate …

Slip Distribution Of The 1952 Kamchatka Great Earthquake Based On Near-Field Tsunami Deposits And Historical Records, Breanyn Macinnes, Robert Weiss, Joanne Bourgeois, Tatiana K. Pinegina

All Faculty Scholarship for the College of the Sciences

We explore the magnitude and slip distribution of the 1952 Kamchatka earthquake (M_W 8.8–9.0) using constraints from the 1952 Kamchatka tsunami. Our new field data provide more comprehensive coverage of the near-field tsunami than had been available to date. We examine the effects of internal slip distribution within complex earthquake ruptures on near-field tsunami runup and evaluate some of the limitations of this approach. Our approach compares tsunami-deposit distribution with simulated runup from tsunamis generated by different configurations of seafloor deformation from hypothetical earthquakes resembling that of the 1952 Kamchatka earthquake. We identify areas of high slip because different …

Moment Release Rate Of Cascadia Tremor Constrained By Gps, Ana C. Aguiar, Timothy I. Melbourne, Craig W. Scrivner

All Faculty Scholarship for the College of the Sciences

A comparison of GPS and seismic analyses of 23 distinct episodic tremor and slip events, located throughout the Cascadia subduction zone over an 11-year period, yields a highly linear relationship between moment release, as estimated from GPS, and total duration of nonvolcanic tremor, as summed from regional seismic arrays. The events last 1–5 weeks, typically produce ~5 mm of static forearc deformation, and show cumulative totals of tremor that range from 40 to 280 h. Moment released by each event is estimated by inverting GPS-measured deformation, which is sensitive to all rates of tremor-synchronous faulting, including aseismic creep, for total …

Seismic Observations Of Transient Subglacial Water-Flow Beneath Macayeal Ice Stream, West Antarctica, J. Paul Winberry, Sridhar Anandakrishnan, Richard B. Alley

All Faculty Scholarship for the College of the Sciences

New seismic observations of harmonic tremors beneath MacAyeal Ice Stream, West Antarctica are reported. Each of the two tremor events that we recorded during a six week period had sustained arrival of 3 Hz energy for approximately 10 minutes. During that time the source location migrated a few kilometers. The harmonic nature of the tremors is interpreted as the result of resonance in subglacial water-filled cracks and conduits. The duration, monochromatic nature, and movement of the tremor indicate that the source mechanism is likely flow in the subglacial water system resulting from the discharge from a small subglacial lake. Our …

Kinematic Behavior Of Southern Alaska Constrained By Westward Decreasing Postglacial Slip Rates On The Denali Fault, Alaska, A.-S. Mériaux, K. Sieh, R. C. Finkel, Charles M. Rubin, M. H. Taylor, A. J. Meltzner, F. J. Ryerson

All Faculty Scholarship for the College of the Sciences

Long‐term slip rates for the Denali Fault in southern Alaska are derived using ¹⁰Be cosmogenic radionuclide (CRN) dating of offset glacial moraines at two sites. Correction of ¹⁰Be CRN model ages for the effect of snow shielding uses historical, regional snow cover data scaled to the site altitudes. To integrate the time variation of snow cover, we included the relative changes in effective wetness over the last 11 ka, derived from lake‐level records and δ ¹⁸O variations from Alaskan lakes. The moraine CRN model ages are normally distributed around an average of 12.1 ± 1.0 ka (n …

Basal Mechanics Of Ice Streams: Insights From The Stick-Slip Motion Of Whillans Ice Stream, West Antarctica, J. Paul Winberry, Sridhar Anandakrishnan, Richard B. Alley, Robert A. Bindschadler, Matt A. King

All Faculty Scholarship for the College of the Sciences

The downstream portion of Whillans Ice Stream, West Antarctica, moves primarily by stick-slip motion. The observation of stick-slip motion suggests that the bed is governed by velocity-weakening physics and that the basal physics is more unstable than suggested by laboratory studies. The stick-slip cycle of Whillans Ice Plain exhibits substantial variability in both the duration of sticky periods and in slip magnitude. To understand this variability, we modeled the forces acting on the ice stream during the stick phase of the stick-slip cycle. The ocean tides introduce changes in the rate at which stress is applied to the ice plain. …

Paleomagnetic Behavior Of Volcanic Rocks From Isla Socorro, Mexico, Elise Sbarbori, Lisa Tauxe, Avto Goguitchaichvili, Jaime Urrutia-Fucugauchi, Wendy A. Bohrson

All Faculty Scholarship for the College of the Sciences

The direction and magnitude of the geomagnetic field vary both spatially and temporally and undergo significant departures from that of a geocentric axial dipole. In order to properly characterize persistent behaviors, time-averaged field models must be based on the highest quality data. Here we present full-vector paleomagnetic data for volcanic units exposed in the southeast quadrant of the island of Socorro, Mexico. We carried out a joint expedition between the Scripps Institution of Oceanography and the Universidad Nacional Autónoma México to Isla Socorro in January of 2005 during which we collected oriented paleomagnetic samples from 21 sites, representing as many …

Geomorphology Of The Southernmost Longitudinal Valley Fault: Implications For Evolution Of The Active Suture Of Eastern Taiwan, J. Bruce H. Shyu, Kerry Sieh, Yue-Gau Chen, Ray Y. Chuang, Yu Wang, Ling-Ho Chung

All Faculty Scholarship for the College of the Sciences

In order to understand fully the deformational patterns of the Longitudinal Valley fault system, a major structure along the eastern suture of Taiwan, we mapped geomorphic features near the southern end of the Longitudinal Valley, where many well‐developed fluvial landforms record deformation along multiple strands of the fault. Our analysis shows that the Longitudinal Valley fault there comprises two major strands. The Luyeh strand, on the west, has predominantly reverse motion. The Peinan strand, on the east, has a significant left‐lateral component. Between the two strands, late Quaternary fluvial sediments and surfaces exhibit progressive deformation. The Luyeh strand dies out …

Serial Ruptures Of The San Andreas Fault, Carrizo Plain, California, Revealed By Three-Dimensional Excavations, Jing Liu-Zeng, Yann Klinger, Kerry Sieh, Charles Rubin, Gordon Seitz

All Faculty Scholarship for the College of the Sciences

It is poorly known if fault slip repeats regularly through many earthquake cycles. Well‐documented measurements of successive slips rarely span more than three earthquake cycles. In this paper, we present evidence of six sequential offsets across the San Andreas fault at a site in the Carrizo Plain, using stream channels as piercing lines. We opened a latticework of trenches across the offset channels on both sides of the fault to expose their subsurface stratigraphy. We can correlate the channels across the fault on the basis of their elevations, shapes, stratigraphy, and ages. The three‐dimensional excavations allow us to locate accurately …

Estimation Of Iron Solubility From Observations And A Global Aerosol Model, Chao Luo, N. M. Mahowald, N. Meskhidze, Y. Chen, R. L. Siefert, A. R. Baker, Anne M. Johansen

All Faculty Scholarship for the College of the Sciences

Mineral aerosol deposition is the dominant source of iron to the open ocean. Soil iron is typically insoluble and understanding the atmospheric processes that convert insoluble iron to the more soluble forms observed over the oceans is crucial. In this paper, we model several proposed processes for the conversion of Fe(III) to Fe(II), and compare with cruise observations. The comparisons show that the model results in similar averaged magnitudes of iron solubility as measured during 8 cruises in 2001–2003. Comparisons show that results of cases including cloud, SO₂ and hematite processing are better than the other approaches used using …

Southern Cascadia Episodic Slow Earthquakes, Walter Szeliga, Timothy I. Melbourne, M. Meghan Miller, V. Marcelo Santillan

All Faculty Scholarship for the College of the Sciences

Continuous GPS and seismic data from northern California show that slow earthquakes periodically rupture the Gorda‐North America plate interface within southern Cascadia. On average, these creep events have occurred every 10.9 ± 1.2 months since at least 1998. Appearing as week‐long GPS extensional transients that reverse secular forearc contraction, the data show a recurrence interval 22% shorter than slow events recognized to the north. Seismic tremor here accompanies the GPS reversals, correlated across as many as 5 northern California seismometers. Tremor occurs sporadically throughout the year, but increases in duration and intensity by a factor of about 10 simultaneous with …

Quantitative Analysis Of Movement Along An Earthquake Thrust Scarp: A Case Study Of A Vertical Exposure Of The 1999 Surface Rupture Of The Chelungpu Fault At Wufeng, Western Taiwan, Jian-Cheng Lee, Charles Rubin, Karl Mueller, Yue-Gau Chen, Yu-Chang Chan, Kerry Sieh, Hao-Tsu Chu, Wen-Shan Chen

All Faculty Scholarship for the College of the Sciences

A vertical exposure across the principal thrust scarp of the 1999 Mw 7.6 earthquake allows quantification of fault slip. The exposure is located on the active Chelungpu fault near Wufeng, along the range front of the fold-and-thrust belt in western Taiwan. The 1999 surface ruptures at the Wufeng site are characterized by a west-facing 2 to 3 m high principal thrust scarp and an east-facing lesser backthrust scarp. We mapped a 15 m-long, 5 m-deep exposure across the principal thrust scarp and characterized complex deformation structures, which include a main basal thrust fault, a wedge thrust, and a pop-up anticlinal …

Error Analysis Of Continuous Gps Position Time Series, Simon D. P. Williams, Yehuda Bock, Peng Fang, Paul Jamason, Rosanne M. Nikolaidis, Linette Prawirodirdjo, Meghan Miller, Daniel J. Johnson

All Faculty Scholarship for the College of the Sciences

A total of 954 continuous GPS position time series from 414 individual sites in nine different GPS solutions were analyzed for noise content using maximum likelihood estimation (MLE). The lengths of the series varied from around 16 months to over 10 years. MLE was used to analyze the data in two ways. In the first analysis the noise was assumed to be white noise only, a combination of white noise plus flicker noise, or a combination of white noise plus random walk noise. For the second analysis the spectral index and amplitude of the power law noise were estimated simultaneously …

Detection Of Arbitrarily Large Dynamic Ground Motions With A Dense High-Rate Gps Network, Yehuda Bock, Linette Prawirodirdjo, Timothy I. Melbourne

All Faculty Scholarship for the College of the Sciences

We describe the detection of teleseismic surface waves from the 3 November 2002 Mw 7.9 Denali fault earthquake in Alaska with a dense network of 1 Hz GPS stations in southern California, about 3900 km from the event. Relative horizontal displacements with amplitudes in excess of 15 mm and duration of 700 seconds agree with integrated velocities recorded by nearby broadband seismometers with an rms difference of 2–3 mm. The displacements are derived from independent 1 Hz instantaneous positions demonstrating that a GPS network can provide direct measurements of arbitrarily large dynamic and static ground horizontal displacements at periods longer …

Energy‐Constrained Open‐System Magmatic Processes Iv: Geochemical, Thermal And Mass Consequences Of Energy‐Constrained Recharge, Assimilation And Fractional Crystallization (Ec‐Rafc), Wendy A. Bohrson, Frank J. Spera

All Faculty Scholarship for the College of the Sciences

A wealth of geochemical and petrological data provide evidence that the processes of fractional crystallization, assimilation, and magma recharge (replenishment) dominate the chemical signatures of many terrestrial igneous rocks. Previous work [Spera and Bohrson, 2001; Bohrson and Spera, 2001] has established the importance of integrating energy, species and mass conservation into simulations of complex magma chamber processes. An extended version of the energy‐constrained formulation, Energy‐Constrained Recharge, Assimilation, Fractional Crystallization (EC‐RAFC), tracks mass and compositional variations of melt, cumulates, and enclaves in a magma body undergoing simultaneous recharge, assimilation, and fractional crystallization [Spera and Bohrson, 2002]. …

Rapid Postseismic Transients In Subduction Zones From Continuous Gps, Timothy I. Melbourne, Frank H. Webb, Joann M. Stock, Christoph Reigber

All Faculty Scholarship for the College of the Sciences

Continuous GPS time series from three of four recently measured, large subduction earthquakes document triggered rapid postseismic fault creep, representing an additional moment release upward of 25% over the weeks following their main shocks. Data from two M_w = 8.0 and M_w = 8.4 events constrain the postseismic centroids to lie down dip from the lower limit of coseismic faulting, and show that afterslip along the primary coseismic asperities is significantly less important than triggered deep creep. Time series for another M_w = 7.7 event show 30% postseismic energy release, but here we cannot differentiate between afterslip …

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 …

Present Day Kinematics Of The Eastern California Shear Zone From A Geodetically Constrained Block Model, S. C. Mcclusky, S. C. Bjornstad, B. H. Hager, R. W. King, B. J. Meade, M. Meghan Miller, F. C. Monastero, B. J. Souter

All Faculty Scholarship for the College of the Sciences

We use Global Positioning System (GPS) data from 1993–2000 to determine horizontal velocities of 65 stations in eastern California and western Nevada between 35° and 37° N. We relate the geodetic velocities to fault slip rates using a block model that enforces path integral constraints over geologic and geodetic time scales and that includes the effects of elastic strain accumulation on faults locked to a depth of 15 km. The velocity of the Sierra Nevada block with respect to Nevada is 11.1±0.3 mm/yr, with slip partitioned across the Death Valley, (2.8±0.5 mm/yr), Panamint Valley (2.5±0.8 mm/yr), and Airport Lake/Owens Valley …

Gps-Determination Of Along-Strike Variation In Cascadia Margin Kinematics: Implications For Relative Plate Motion, Subduction Zone Coupling, And Permanent Deformation, M. Meghan Miller, Daniel J. Johnson, Charles M. Rubin, Herb Dragert, Kelin Wang, Anthony Qamar, Chris Goldfinger

All Faculty Scholarship for the College of the Sciences

High‐precision GPS geodesy in the Pacific Northwest provides the first synoptic view of the along‐strike variation in Cascadia margin kinematics. These results constrain interfering deformation fields in a region where typical earthquake recurrence intervals are one or more orders of magnitude longer than the decades‐long history of seismic monitoring and where geologic studies are sparse. Interseismic strain accumulation contributes greatly to GPS station velocities along the coast. After correction for a simple elastic dislocation model, important residual motions remain, especially south of the international border. The magnitude of northward forearc motion increases southward from western Washington (3–7 mm/yr) to northern …

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 …

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 …

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 …