All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1294.
Modeling evolution of the San Andreas Fault system in northern and central California
Geochemistry, Geophysics, Geosystems,
13
(8)
2012
ISSN: 15252027
Publisher: Blackwell Publishing Ltd
Keywords:▾
Friction; Geodynamics; Plates (structural components); Strike-slip faults; Tectonics, Best-fit models; California; Coefficient of frictions; Complex deformation; Cooling mechanism; Crustal block; Driving mechanism; Elasto-viscoplastic; Free surfaces; Microplates; Nonlinear temperature; Numeric models; Pacific plates; Plate boundaries; San Andreas fault; Self-generation; Slab windows; Stress-dependent; Subduction zones; Thermomechanical model; Three dimensional finite elements; weak fault in strong crust, Three dimensional, deformation; finite element method; friction; geodynamics; numerical model; Pacific plate; plate boundary; San Andreas Fault; subduction zone; tectonic evolution, California; United States
Abstract: ▾ We present a three-dimensional finite element thermomechanical model idealizing the complex deformation processes associated with evolution of the San Andreas Fault system (SAFS) in northern and central California over the past 20 Myr. More specifically, we investigate the mechanisms responsible for the eastward (landward) migration of the San Andreas plate boundary over time, a process that has largely determined the evolution and present structure of SAFS. Two possible mechanisms had been previously suggested. One mechanism suggests that the Pacific plate first cools and captures uprising mantle in the slab window, subsequently causing accretion of the continental crustal blocks. An alternative scenario attributes accretion to the capture of plate fragments (microplates) stalled in the ceased Farallon-North America subduction zone. Here we test both these scenarios numerically using a recently developed lithospheric-scale code, SLIM3D, that employs free surface, nonlinear temperature- and stress-dependent elastoviscoplastic rheology and allows for self-generation of faults. Modeling suggests that microplate capture is the primary driving mechanism for the eastward migration of the plate boundary, while the slab window cooling mechanism alone is incapable of explaining this phenomenon. We also show that the system evolves to the present day structure of SAFS only if the coefficient of friction at mature faults is low (0.08 for the best fit model). Thus, our model provides an independent constraint supporting the "weak fault in a strong crust" hypothesis for SAFS. © 2012. American Geophysical Union. All Rights Reserved.
1293.
Solute geochemistry and its sources of the groundwaters in the Qinghai Lake catchment, NW China
Journal of Asian Earth Sciences,
5221 – 30
2012
ISSN: 13679120Keywords:▾
China; Himalayas; Qinghai; Qinghai-Xizang Plateau; catchment; dissolution; groundwater; ion exchange; ionic composition; river water; solute; water quality; weathering
Abstract: ▾ Major ion compositions were analyzed in 65 groundwater samples to decipher water quality, solute geochemistry and sources of groundwater within the Qinghai Lake catchment, NE Tibetan Plateau. Groundwaters were slightly alkaline with pH varying from 7.2 to 8.7. The total dissolved solids (TDS) varied over two orders of magnitude from fresh (88%) to brackish (12%) with a mean value of 672mg/L, higher than river waters within the Qinghai Lake catchment and river waters draining the Himalayas and the southeastern Tibetan Plateau. Most of the samples, approximately 80%, were the Ca 2+-Mg 2+-HCO3- type and suitable for drinking and irrigation. Some of the Lakeside, the Buha and the Qinghai Lake water were the Na +-Cl - type and not suitable for drinking and irrigation. Water quality of Hargai and Shaliu samples was better than the others. Rock weathering, ion exchange and precipitation are the major geochemical processes responsible for the solutes in the groundwater within the Qinghai Lake catchment. Anthropogenic input to the groundwater is minor. The forward models on the input of groundwaters from various sources showed that the contributions were 40.1% for carbonate weathering, 29.0% for evaporite dissolution, 16.8% for atmospheric input and 14.1% for silicate weathering of the total dissolved cations for the whole catchment. Evaporite dissolution was dominating in the Lakeside, the Buha and the Daotang samples, contributing 15.3-45.9%, 20.4-61.1% and 21.3-63.9% of the total dissolved cations, respectively. Carbonate weathering was dominated in the Shaliu and the Hargai samples, contributing 23.9-71.7% and 31.8-95.4% of the total dissolved cations, respectively. The result also demonstrated that carbonate weathering had higher contribution to the groundwaters than silicate weathering. © 2012 Elsevier Ltd.
1292.
Mineralogy of the otoliths of naked carp Gymnocypris przewalskii (Kessler) from Lake Qinghai and its Sr/Ca potential implications for migratory pattern
Science China Earth Sciences,
55
(6)
983 – 990
2012
ISSN: 16747313
Publisher: Science in China Press
Keywords:▾
China; Qinghai; Qinghai Lake; Qinghai-Xizang Plateau; Asteriscus; Cyprinidae; Gymnocypris przewalskii; Sagitta; Carbonate minerals; Chemical analysis; Fourier transform infrared spectroscopy; Minerals; X ray diffraction; aragonite; Environmental tracers; Lake Qinghai naked carps; migration; otolith; Sr/ca ratios; aragonite; biogenic mineral; calcium; chemical composition; crystallization; cyprinid; mineralogy; otolith; strontium; tracer; Lakes
Abstract: ▾ Otoliths are biogenic carbonate minerals whose microstructure and microchemistry have been used for age determination, stock identification, life history and environmental tracing. Using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, we have determined the mineral types and crystalline characteristics of three pairs of otoliths from naked carp Gymnocypris przewalskii, the predominant fish in Lake Qinghai. The results indicate that the mineral of both lapillus and sagitta of the naked carp is aragonite, and that of asteriscus is vaterite. The aragonite of lapillus has prefect crystallization. Given the shape of lapillus and the sensitivity of its aragonite to water chemistry, lapillus was used to analyze temporal Sr/Ca ratios along the maximal growth axis by an electron probe microanalyzer (EPMA). Consistent variations of Sr/Ca ratios with a range of 1. 0×10-3-5. 0×10{combining triple dot above} on the long and short radii indicate that Sr/Ca ratios of lapillus potentially respond to the chemical compositions of the host waters during the period of the naked carp's growth and migration. Discontinuous (dark) zones of lapillus were formed during fall and winter when the naked carp grows slowly in Lake Qinghai, resulting in similar low Sr/Ca ratios to lake water, whereas incremental zones with higher Sr/Ca ratios respond to its migratory river waters during spring and summer. Various Sr/Ca ratios of incremental zones suggest that the migratory pattern of the naked carp may be much more flexible, rather than in a single river. Therefore, high-resolution otolith microchemistry of the naked carp can be used to trace its migratory behavior, which is of significance for determining its migratory pattern and life history of this precious species inhabiting the Tibetan Plateau. © 2012 Science China Press and Springer-Verlag Berlin Heidelberg.
1291.
Shear wave anisotropy from cross-correlation of seismic noise in the Parkfield pilot hole
Geophysical Journal International,
188
(2)
626-630
2012
ISSN: 0956540XKeywords:▾
Body waves; Cross correlations; Drilling noise; P- and S-waves; Pilot holes; Polarization direction; S-wave velocity; S-waves; San Andreas Fault; Seismic anisotropy; Seismic noise; Shear-wave anisotropy; Three-component, Anisotropy; Interferometry; Polarization; Seismology; Shear waves; Velocity measurement, Shear flow, borehole; correlation; interferometry; P-wave; S-wave; San Andreas Fault; seismic anisotropy; seismic noise; wave propagation; wave velocity, California; Parkfield; United States
Abstract: ▾ We use cross-correlation of seismic noise recorded at stations in the San Andreas Fault Observatory at Depth (SAFOD) pilot hole to extract P and S waves and measure S-wave anisotropy on the horizontal components. The data are recorded at seven three-component stations at depths from 1857 to 2097 m in the pilot hole. In late September and early 2004 October drilling noise underneath the stations generated propagating waves, which were absent in the rest of October. Estimates of the P- and S-wave velocities from the cross-correlations, on the vertical and horizontal components, respectively, are consistent with velocity measurements taken directly in the borehole. We observe polarization of the S wave, with a fast polarization direction of 120°-130° that is 4 per cent faster than the slow direction. Cross-correlation of the seismic noise can accurately determine S-wave anisotropy. © 2011 The Authors Geophysical Journal International © 2011 RAS.
1290.
[English]
Stochastic connectivity analysis and volume estimation at the Mallik gas hydrate reservoir, Mackenzie Delta, Canada
Page 496-501
Publisher
Society of Exploration Geophysicists
2012
INRS-ETE, Canada; Geological Survey, Canada; Ecole Polytechnique de Montréal, CanadaKeywords:▾
Acoustic fields; Acoustic impedance; Gases; Geophysical prospecting; Hydration; Petroleum prospecting; Stochastic models; Stochastic systems; Uncertainty analysis; Well logging, Bayesian simulation; Connectivity analysis; Different grades; Gas hydrate reservoir; Simulation approach; Statistical relations; Volume estimations; Well log data, Gas hydrates
ISBN:
9781622769452
1289.
Source Characterization of near-surface chemical explosions at SAFOD
Bulletin of the Seismological Society of America,
102
(4)
1348-1360
2012
ISSN: 00371106Keywords:▾
Chemical explosions; Downholes; First-order; Forward modeling; Grid search; High frequency HF; Moment ratio; Near-surface; Receiver array; San Andreas fault; Second orders; Seismic recording; Source characterization; Source parameters; Static moment; Vertical shear; Volume change, Strike-slip faults, Explosions, moment tensor; nuclear explosion; seismic attenuation; seismic velocity; seismic wave; source parameters
Abstract: ▾ A series of near-surface chemical explosions conducted at the San Andreas Fault Observatory at Depth (SAFOD) main hole were recorded by highfrequency downhole receiver arrays in April 2005. These seismic recordings at depths ranging from the surface to 2.3 km constrain the shallow velocity and attenuation structure as well as the first-order characteristics of the source. Forward modeling of the explosions indicates that a source consisting of combined explosion, delayed implosion, and second-order moment-tensor components (corresponding to a distribution of vertical shear dislocations in the rock directly above the explosion) is sufficient to characterize the generated seismic wave fields to first order. Grid searches over source parameters controlling the nonexplosive components allow for the quantification of distributed vertical shear above the source and the estimation of the moment and time delay of the implosive component relative to the explosion. An estimated implosive to explosive moment ratio of 0.34 to 0.43 indicates a net static moment and positive macroscopic volume change.
1288.
Workshop on drilling of Lake Junin, Peru: Potential for development of a continuous tropical climate record
Scientific Drilling
(13)
58-60
2012
ISSN: 181689571287.
Methanotrophy in a P aleoproterozoic oil field ecosystem, Z aonega F ormation, K arelia, R ussia
Geobiology,
10
(6)
467--478
2012
1286.
FAR-DEEP Core Archive: Further Opportunities for Earth Science Research and Education
Reading the Archive of Earth’s Oxygenation: Volume 3: Global Events and the Fennoscandian Arctic Russia-Drilling Early Earth Project
Page 1537--1552
Publisher
Springer
2012
1537--15521285.
1 The International Continental Scientific Drilling Program
Reading the Archive of Earth’s Oxygenation: Volume 1: The Palaeoproterozoic of Fennoscandia as Context for the Fennoscandian Arctic Russia-Drilling Early Earth Project
Page 25--30
Publisher
Springer
2012
25--301284.
1 The Imandra/Varzuga Greenstone Belt
Reading the Archive of Earth’s Oxygenation: Volume 1: The Palaeoproterozoic of Fennoscandia as Context for the Fennoscandian Arctic Russia-Drilling Early Earth Project
Page 249--287
Publisher
Springer
2012
249--2871283.
[English]
Velocity dispersion of stoneley wave as an insight into permeability
Page 1839-1843
Publisher
European Association of Geoscientists and Engineers, EAGE
2012
China University of Petroleum, China; University of Toronto, CanadaISBN:
9781629937908
1282.
[English]
Seismic imaging of gas hydrate accumulations beneath thick permafrost areas of the Mackenzie Delta, NWT, Canada
Volume 2
,
Page 560-569
Publisher
Society of Petroleum Engineers
2012
Geological Survey of Canada, CanadaDOI:10.4043/23767-ms
Keywords:▾
Acoustic impedance; Aquifers; Boreholes; Gases; Gasoline; Hydration; Oil well logging; Permafrost; Petroleum prospecting; Seismic prospecting; Seismic response; Seismic waves; Shear waves; Wave propagation; Well logging, Conventional hydrocarbons; Conventional oil and gas; Hydrate accumulations; P- and S-wave velocities; Relative amplitude; Seismic reflections; Seismic signatures; Velocity contrasts, Gas hydrates
ISBN:
9781627482899
1281.
[English]
Gas hydrate reservoir modeling and validation
Publisher
European Association of Geoscientists and Engineers, EAGE
2012
INRS-ETE, France; École Polytechnique, FranceKeywords:▾
Acoustic impedance; Energy resources; Gases; Hydration; Reservoir management; Resource valuation; Seismology, 3D seismic data; Bayesian algorithms; Gas hydrate reservoir; Gas reservoir; High resolution seismic; Tomographic inversion; Unconventional gas; Unconventional resources, Gas hydrates
1280.
The Cretaceous-tertiary mass extinction, Chicxulub impact, and Deccan volcanism
2012
1279.
Projectile Identification in Terrestrial Impact Structures and Ejecta Material
2012
1278.
1277.
1276.
Fault-zone trapped waves: High-resolution characterization of the damage zone of the Parkfield San Andreas fault at depth
Publisher
Walter de Gruyter GmbH and Co. KG
2012
1275.
Vegetation history of central Chukotka deduced from permafrost paleoenvironmental records of the El'gygytgyn Impact Crater
Climate of the Past,
8
(4)
1287-1300
2012
ISSN: 18149324Keywords:▾
climate change; environmental change; Hypsithermal; paleoenvironment; permafrost; sediment core; temporal record; treeline; vegetation history, Chukchi; Elgygytgyn Lake; Russian Federation
Abstract: ▾ Frozen sediments from three cores bored in the permafrost surrounding the El'gygytgyn Impact Crater Lake have been studied for pollen, non-pollen palynomorphs, plant macrofossils and rhizopods. The palynological study of these cores contributes to a higher resolution of time intervals presented in a poor temporal resolution in the lacustrine sediments; namely the Allerød and succeeding periods. Moreover, the permafrost records better reflect local environmental changes, allowing a more reliable reconstruction of the local paleoenvironments. The new data confirm that shrub tundra with dwarf birch, shrub alder and willow dominated the lake surroundings during the Allerød warming. Younger Dryas pollen assemblages reflect abrupt changes to grass-sedge-herb dominated environments reflecting significantly drier and cooler climate. Low shrub tundra with dwarf birch and willow dominate the lake vicinity at the onset of the Holocene. The find of larch seeds indicate its local presence around 11 000 cal yr BP and, thus a northward shift of treeline by about 100 km during the early Holocene thermal optimum. Forest tundra with larch and shrub alder stands grew in the area during the early Holocene. After ca. 3500 cal yr BP similar-to-modern plant communities became common in the lake vicinity. © 2009 Author(s).
1274.
Stochastic volume estimation and connectivity analysis at the Mallik gas hydrate field, Northwest Territories, Canada
Leading Edge,
31
(9)
1076-1081
2012
ISSN: 1070485X
Publisher: Society of Exploration Geophysicists
Keywords:▾
Acoustic impedance; Energy resources; Gases; Hydration; Natural gas; Natural gas deposits; Offshore oil well production; Permafrost; Petroleum deposits; Seismic prospecting; Seismology; Shear waves; Stochastic systems, Connectivity analysis; Economic potentials; Hydrate accumulations; Natural gas resources; P- and S-wave velocities; Scientific literature; Seismic amplitudes; Volume estimations, Gas hydrates, connectivity; estimation method; gas hydrate; natural gas; permafrost; S-wave; stochasticity, Alaska; Canada; Northwest Territories; United States
Abstract: ▾ Gas hydrates located offshore and onshore beneath thick permafrost areas constitute one of the largest untapped natural gas resources. Yet, gas hydrate in place (GHIP) estimation at the scale of a field is not common in the scientific literature but is required to realistically assess the economical potential of specific accumulations. Progress in the last decade in Alaska and Canada has shown that gas hydrate accumulations beneath thick permafrost can be mapped at depth using conventional seismic attributes (Inks et al., 2009; Riedel et al. 2009). To evaluate the economic potential of gas hydrates in this environment, a test site at Mallik, Northwest Territories, Canada, was extensively surveyed (three-dimensional seismic, full set of logs in two wells, etc.) and a production test was realized in high gas-hydrate horizons. At Mallik, high P- and S-wave velocities, high acoustic impedances, and strong seismic amplitude reflections were all linked to sand-rich sediments with a high saturation of gas hydrates (Bellefleur et al. 2006; Riedel et al.). This relationship provides a strong basis for an integrated data characterization of this gas hydrate deposit. © 2012 Society of Exploration Geophysicists.
1273.
U-Pb, trace element and Lu-Hf properties of unique dissolution-reprecipitation zircon from UHP eclogite in SW Sulu terrane, eastern China
Gondwana Research,
22
(1)
169 – 183
2012
ISSN: 1342937XAbstract: ▾ A unique dissolution-reprecipitation zircon has been identified for the first time in a Qtz- and Phe-bearing eclogite from the drill hole CCSD-MH, southwestern Sulu UHP terrane by using laser Raman and cathodoluminescence (CL) imaging combined with trace-element analyses and U-Pb and Lu-Hf isotope data. Relic inherited domains of partially dissolved zircon show magmatic features and preserve mineral inclusions of Cpx+Pl+Qtz+Ap. Whereas newly formed zircons crystallized around or along cracks of the inherited (magmatic) domains and contain mineral inclusions of Coe+Grt+Omp+Phe+Ap typical for UHP metamorphism. In addition, primary fluid inclusions were identified in the coesite-bearing zircon domains, characterized by a single H 2O-phase or CO 2-H 2O-phase, indicating the presence of fluids during UHP conditions. Strongly dissolved inherited (magmatic) zircons yielded SHRIMP 206Pb/ 238U ages of 782-588Ma with an upper intercept age of 780±14Ma. New recrystallized or metamorphic zircons yielded consistent Triassic UHP ages around 238-225Ma with a weighted mean of 229.2±2.3Ma. Zircon trace element and Hf isotope compositions and mineral inclusions classify the protolith of the Sulu eclogite as an intermediate to mafic Neoproterozoic igneous rock, which was subducted to mantle depth and experienced UHP metamorphism in Middle Triassic times. The juvenile εHf (780Ma) value of+7.4±2.9 in inherited (magmatic) zircon points to a significant input from the depleted mantle to the Dabie-Sulu UHP terrane during Middle Neoproterozoic. New UHP zircon domains have low Lu/Hf, Th/U and significantly higher 176Hf/ 177Hf ratios than the inherited (magmatic) zircons, consistent with formation during recrystallization and fractionation of the Lu-Hf system during UHP metamorphism. © 2011 International Association for Gondwana Research.
1272.
Tsunami backwash deposits with Chicxulub impact ejecta and dinosaur remains from the Cretaceous-Palaeogene boundary in the La Popa Basin, Mexico
Sedimentology,
59
(3)
737-765
2012
Abstract: ▾ The La Popa Basin in north-eastern Mexico features outstanding, continuous three-dimensional exposures of the Cretaceous-Palaeogene boundary event deposit in shallow shelf environments pierced by salt stocks. In the area to the south-east of the El Papalote diapir, the Cretaceous-Palaeogene deposit consists of two superimposed sedimentary units and erosively overlies upper Maastrichtian sand-siltstones with soft-sediment deformation and liquefaction structures. The basal unit 1 is an up to 8m thick chaotic, carbonate-rich bed that discontinuously fills incised gutters and channels. Besides abundant silicic and carbonate ejecta spherules from the Chicxulub impact, unit 1 includes large sandstone boulders and abundant shallow-water debris (for example, mud clasts, algae, bivalve shells, gastropod shells and vertebrate remains). Unit 1 is conformably overlain by unit 2. Distal to the diapir, unit 2 consists of a centimetre to decimetre-thick conglomeratic, coarse bioclast and spherule-bearing sandstone bed. Closer to the diapir, unit 2 becomes a metre-thick series of four to eight conglomeratic to fine-grained graded sandstone beds rich in shell debris and ejecta spherules. Unit 2 is conformably overlain by structureless to parallel laminated sandstone beds that may mark the return to the pre-event depositional regime. The sedimentary characteristics of the Cretaceous-Palaeogene deposit, including its erosive base, its sheet-like geometry, the presence of multiple, graded beds, evidence for upper flow regime conditions and the absence of bioturbation, support an origin by a short-term multiphase depositional event. The occurrence of soft-sediment deformation structures (for example, liquefaction) below the Cretaceous-Palaeogene deposit suggests that earthquakes were the first to occur at La Popa. Then, shelf collapse and strong backflow from the first tsunami waves may have triggered erosion and deposition by violent ejecta-rich hyperconcentrated density flows (unit 1). Subsequently, a series of concentrated density flows resulting from tsunami backwash surges may have deposited the multiple-graded bedding structures of unit 2. The specific depositional sequence and the Fe-Mg-rich as well as Si-K-rich composition of the ejecta spherules both provide a critical link to the well-known deep marine Cretaceous-Palaeogene boundary sites in the adjacent Burgos basin in north-eastern Mexico. Moreover, the pulse-like input of Chicxulub ejecta material at the base of the event deposit allows for correlation with other Cretaceous-Palaeogene boundary sites in the Gulf of Mexico and the Atlantic, as well as in Central and Northern America. The presence of diverse dinosaur and mosasur bones and teeth in the event deposit is the first observation of such remains together with Chicxulub ejecta material. These findings indicate that dinosaurs lived in the area during the latest Maastrichtian and suggest that the tsunami waves not only eroded deltas and estuaries but the coastal plain as well. © 2011 The Authors. Journal compilation © 2011 International Association of Sedimentologists.
1271.
Toward age determination of the termination of the Cretaceous Normal Superchron
Geochemistry, Geophysics, Geosystems,
13
(2)
2012
ISSN: 15252027
Publisher: Blackwell Publishing Ltd
Keywords:▾
Anoxic sediments; Geomagnetism; Lead; Sedimentology, Age determination; Anoxic events; Black shales; Cretaceous Normal Superchron; East Asia; Geomagnetic fields; Geomagnetic polarity; High resolution; Magnetostratigraphy; Northeast China; Oceanic Anoxic Event; Sedimentary sequence; Songliao basin; Time-scales; U-Pb zircon; Upper Cretaceous, Geochronology, anoxic conditions; bentonite; black shale; Cretaceous; geochronology; geomagnetic field; magnetostratigraphy; sedimentary sequence; uranium-lead dating, China; Songliao Basin
Abstract: ▾ We present an integrated chronology for the terrestrial Upper Cretaceous in East Asia based on high-resolution magnetostratigraphic results and detailed SIMS U-Pb zircon analyses of a continuous continental sedimentary sequence drilled from the Songliao Basin in northeast China. Correlation to the geomagnetic polarity timescale was achieved by combining magnetostratigraphic and SIMS U-Pb zircon geochronologic data, which suggest that the south core of the CCSD-SK-I sedimentary sequence spans from upper chron C34n to lower chron C33r. The age of the termination of the Cretaceous Normal Superchron (CNS) was estimated to be ∼83.4 Ma. Intervals of reverse geomagnetic field polarity of early Santonian age could be present during the late CNS. Two black shale layers at the base of Member 1 of the Qingshankou Formation and Member 2 of the Nenjiang Formation, which were previously interpreted as the products of lake anoxic events LAE1 and LAE2, have been well dated at 91.4 Ma and 83.7 Ma, respectively, by SIMS U-Pb zircon analyses of intercalated bentonite layers. However, the LAE1 and LAE2 identified here are not temporally correlated to the known oceanic anoxic events. Copyright 2012 by the American Geophysical Union.
1270.
Tomographic V p and V s structure of the California Central Coast Ranges, in the vicinity of SAFOD, from controlled-source seismic data
Geophysical Journal International,
190
(3)
1341-1360
2012
ISSN: 0956540XKeywords:▾
Body waves; Continental margin; Controlled source; North America; Seismic tomography, Cluster analysis; Elasticity; Granite; Rock drills; Sedimentary rocks; Seismographs; Seismology; Shear waves; Strike-slip faults; Surveys; Transform faults, Structural geology, body wave; cluster analysis; continental margin; P-wave; S-wave; San Andreas Fault; seismic data; seismic reflection; seismic refraction; seismic source; seismic survey; seismic tomography; seismic velocity; seismograph; seismology; transform fault; upper crust, California; Coast Ranges; San Andreas; United States
Abstract: ▾ A seismic reflection/refraction survey across the San Andreas fault near Parkfield, California, has refined our knowledge of the upper crustal structure of the central California Coast Ranges at the San Andreas Fault Observatory at Depth (SAFOD). The survey consisted of a 46-km-long line of seismographs (25-50 m spacing) and 63 explosions (25-200 kg; nominal spacing of 500 m, with some gaps). The traveltimes of refracted P and S waves from the explosions constitute independent data sets of relatively high quality that were inverted to produce P- and S-wave velocity models (V p, V s) along the profile, extending to as much as 5 km depth. The V p and V s models show a prominent lateral drop in velocities a few hundred metres northeast of SAFOD, between the drill hole and the San Andreas fault. The V p model shows particularly well a southwest-dipping velocity inversion beneath SAFOD, the top of which correlates with a fault penetrated by the drill hole that separates granitic rocks above from sedimentary rocks below. In addition to V p and V s models, a V p/V s model was derived. A V p/V s ratio lower than 1.73 is seen only at depth, in a narrow zone beginning at the target earthquakes for SAFOD and extending downward and northeastward into the North America Plate. Clusters in the parameter space spanned by V p/V s ratios and V p can be identified by two different methods, one more intuitive analytical method and one more abstract method based on neural network techniques. These clusters are correlated to different rock types, based on laboratory and in situ data. These clusters are remapped back into x-z plane along the profile. Prominent features mapped this way include Salinian granitic rocks beneath and west of SAFOD, and a body of sedimentary rocks faulted beneath these granitic rocks along what we and others interpret to be a branch of the Buzzard Canyon Fault (BCF) system. These sedimentary rocks extend from this fault to the San Andreas fault system. Unfortunately, our cluster analysis shows no significant discontinuity at the San Andreas fault, owing presumably to the fact that the San Andreas fault is located within sedimentary rocks having similar elastic properties. This paper is an attempt to 'downward' continue a geological map by geophysical means based on elastic properties of rock samples from the region. © 2012 The Authors Geophysical Journal International © 2012 RAS.