Long dormancy, low slip rate, and similar slip‐per‐event for the Emerson fault, eastern California shear zone

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 earthquake occurred about 20,000 years B.P. The actual bracketing ages for this rupture are likely a few thousand years older because of the mean residence time for the pedogenic carbonate and calibration of the 14C ages by 230Th dating. Despite the large uncertainties, a dormant period of at least 6 kyr to as much as 13 kyr separates the older event from the 9 ka event. Because the scarp formed by the penultimate event is similar in height to the scarp formed by the 1992 Mw 7.3 Landers earthquake, the penultimate rupture was, at least locally, similar in size to the most recent rupture. This similarity supports the concept of characteristic slip for the Emerson fault. Preliminary results from paleoseismic studies at other sites on the 1992 rupture suggest that large ruptures occurred on other nearby faults within a few hundred years of this penultimate event on the Emerson fault. The interseismic period that preceded the 1992 earthquake on the Emerson fault was about 40 times longer than the average interval between large events on the nearby San Andreas fault. Therefore, in comparison to events on the San Andreas fault, the 1992 Landers earthquake was an exceedingly rare event

Tectonic history of the eastern edge of the Alexander Terrane, southeast Alaska

Rocks exposed west of the Coast Plutonic Complex in southern southeast Alaska form an imbricate thrust belt that overprints the tectonic boundary between two of the largest allochthonous crustal fragments in the North American Cordillera, the Insular and Intermontane composite terranes. In the Alexander terrane (Insular composite terrane), lower Paleozoic metavolcanic and metasedimentary rocks (Descon Formation) and dioritic plutons are unconformably overlain by Lower Devonian clastic strata (Karheen Formation). These rocks are overlain locally by Upper Triassic basalt, rhyolite and marine clastic strata (Hyd Group). Upper Jurassic and Lower Cretaceous metavolcanic and metasedimentary strata of the Gravina sequence unconformably overlie the Alexander terrane. The Gravina sequence forms a structural package over 15 km thick and records intermittent arc volcanism along the eastern edge of the Alexander terrane. The Gravina sequence is structurally overlain by upper Paleozoic and lower Mesozoic metamorphosed basaltic strata, marble, and argillite (Alava sequence), and locally by lower Paleozoic supracrustal rocks and orthogneiss (Kah Shakes sequence). Together, these constitute the Taku terrane which we correlate with the Intermontane composite terrane. Local unconformity of Gravina sequence strata over the Alava sequence demonstrates that the Gravina sequence overlapped an earlier structural boundary between the Intermontane and Insular composite terranes. The rocks were deformed in the mid-Cretaceous by west-vergent thrusting that was was broadly coeval with arc magmatism. Deformation involved emplacement of west-directed thrust nappes over the structurally intact and relatively unmetamorphosed Alexander terrane basement. Mid-Cretaceous tonalite, granodiorite, and quartz diorite intrude rocks of the thrust belt and are locally affected by the deformation. Mid-Cretaceous deformation occurred during two episodes that were contemporaneous with the emplacement of large sill-like plutons. Older structures record ductile southwest-vergent folding and faulting, regional metamorphism, and development of axial-planar foliation. The second-generation structures developed during the later stages of southwest-directed thrust faulting, which juxtaposed rocks of contrasting metamorphic pressures and temperatures. Structural, stratigraphic, and geochronologic data indicate that the two phases of regional thrusting in southeast Alaska occurred between 113 Ma and 89 Ma. Rocks in the western part of the thrust belt were uplifted regionally by 70 Ma. Deformation involved the collapse of a marginal basin(s) and a magmatic arc, and overprinted the older tectonic boundary between the Insular composite terrane and the late Mesozoic western margin of North America (at that time the Intermontane composite terrane). Contractional deformation along the length of the thrust belt was broadly coeval with arc magmatism, and thus records intra-arc tectonism. Late Paleocene to early Eocene igneous activity and extensional (?) deformation subsequently affected the thrust belt

Surficial slip distribution on the central Emerson fault during the June 28, 1992, Landers earthquake, California

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 cm, east‐side‐up. The sense of vertical slip across the main fault zone varied along strike, but in most cases it was consistent with the sense of vertical slip in previous earthquakes, as indicated by the locations of areas of older, uplifted, and abandoned alluvial fan surfaces. Although variations in surficial slip have been reported along previous strike‐slip ruptures, our closely spaced slip measurements allow a much more detailed study of slip variability than was possible previously. We document variations in slip as large as 1 m or more over distances ranging from 1–2 km to a few tens of meters, suggesting that strains of the order of 10−1 may have occurred locally within the surficial sediments. The long‐wavelength (kilometer‐scale) variations in surficial slip may be influenced by fault geometry and perhaps by the thickness of unconsolidated sediments. The slip variations over shorter length scales (tens of meters) may be caused by variations in the proportion of the total shear that occurs on visible, brittle fractures versus that which occurs as distributed shear, warping or rotation. The variability of slip along the ruptures associated with the Landers earthquake calls for caution in interpreting geomorphic offsets along prehistoric fault ruptures

Economic and Fiscal Impacts of Proposed LNG Facility in Robbinston, Maine

The purpose of this study is to examine the economic and fiscal impacts of the proposed Downeast LNG facility on the Town of Robbinston, Washington County, and the State of Maine. The economic impact analysis focuses on the employment and income that are associated with the LNG facility construction and operations. The fiscal impact analysis considers additional local and state tax revenues associated with the facility, as well as increased local government expenditures that are projected to result from the LNG project. This report does not address the environmental, homeland security, or energy security impacts of the LNG facility. In addition, this report does not estimate any changes in the price of delivered natural gas in Maine that could potentially result from a new major energy supplier

Sustainable Transportation for Maine’s Future

Maine is dependent on its transportation infrastructure for continued economic strength and growth, particularly on the 22,670 miles of public roads. Maine ranks fourteenth in the nation for the largest number of highway miles traveled annually per capita - 14,912 per year. Maine is highly reliant on its road system because large areas of the State lack transportation alternatives. This means that the current and future condition of the roadways is a major concern. How such a crucial infrastructure will continue to be supported and enhanced financially to meet the growing needs of the State must be considered carefully

The Gravina Sequence: Remnants of a Mid-Mesozoic oceanic arc in southern southeast Alaska

Fragments of Upper Jurassic to Lower Cretaceous volcanic and basinal strata constitute the Gravina belt in southeast Alaska. In the Ketchikan area the Gravina belt is made up of two lithotectonic units. The lower unit consists of coarse marine pyroclastic and volcaniclastic strata, mafic flows, breccia, and fine-grained tuff which are locally intruded by hypabyssal bodies of diorite and quartz diorite. The volcanic rocks are characterized by tholeiitic arc basalts, lack felsic volcanic strata, and overlie Upper Triassic and older strata of the Alexander terrane. Augite and/or hornblende-bearing porphyritic rocks are common and locally intrude the Alexander terrane basement, where they are thought to represent the intrusive equivalents of lavas within the section. Age constraints for the volcanic unit, based on structural and stratigraphic relations with adjacent units, are late Middle to Late Jurassic. The Gravina belt upper unit consists of fine- to coarse-grained turbidites and related conglomeratic channel-fill deposits. The basinal rocks unconformably overlie Permian and Triassic rocks of the Taku terrane and remnants of the lower volcanic part of the Gravina sequence which overlie the Alexander terrane. The conglomerate units contain mostly volcanic and plutonic lithic clasts, some of which yield Pb-U zircon ages of 154–158 Ma. The predominance of pyroclastic deposits interbedded with massive flows, tuff, breccia, and argillaceous turbidites, and the lithologic and chemical composition of the volcanic rocks indicate a submarine volcanic arc setting for the Gravina sequence. The basinal pyroclastic rocks are inferred to have been shed from submarine stratovolcanos during the Late Jurassic. Epiclastic rocks were deposited as submarine fans, derived in part from erosion of a magmatic arc. The presence of fine-grained tuffaceous turbidites implies ongoing, but distant, volcanism. The pyroclastic and volcaniclastic rocks represent remnants of a Late Jurassic oceanic arc constructed on a composite basement consisting of the Alexander and Taku terranes. The strata accumulated in an intra-arc basin on the eastern edge of the Alexander terrane. The volcanic and basinal rocks were deformed during a major mid-Cretaceous intra-arc contractional event, in conjunction with the emplacement of a distinctly younger, arc-related plutonic suite

Late Quaternary slip rates across the central Tien Shan, Kyrgyzstan, central Asia

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 aid in their regional correlation. Monte Carlo simulations that sample from normally distributed and discrete probability distributions for each variable in the slip rate calculations generate most likely slip rate values and 95% confidence limits. Faults in basins appear to merge at relatively shallow depths with crustal‐scale ramps that underlie mountain ranges composed of pre‐Cenozoic rocks. The sum and overall pattern of late Quaternary rates of shortening are similar to current rates of north‐south shortening measured using Global Positioning System geodesy. This similarity suggests that deformation is concentrated along major fault zones near range‐basin margins. Such faults, separated by rigid blocks, accommodate most of the shortening in the upper crust

Anisotropic ultrasonic backscatter from the renal cortex

We have demonstrated a significant, directionally dependent, anisotropic, echogenicity from the cortices of two sheep kidneys and a normal human cadaver kidney. The anisotropy corresponds to the relationship of the sound field to the medullary rays and interlobular arteries. At 7.5 MHz, the backscatter from specimens of cortex of a sheep kidney was 4.7 +/- .7 dB (mean +/- SEM) greater in parts of the cortex where the field was perpendicular to these structures as opposed to where it was parallel to them. In addition, we measured the angular distribution of this anisotropy and compared it to the 5 dB inclusion angle of the 5 MHz linear array that was used in measurements on the whole kidney specimens. The transducer inclusion angle was 10[deg] +/- 2[deg], while the angular distribution was 34[deg] +/- 22[deg] and 23[deg] +/- 11[deg] (mean +/- SD) for the intact sheep and human kidney, respectively, demonstrating some variation of the medullary rays from perfect specular reflectors. This anisotropy should be visible in standard diagnostic scanning, and its recognition could increase ultrasound's sensitivity for the detection of renal disease.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27571/1/0000615.pd

Highly Variable Recurrence of Tsunamis In the 7,400 Years Before the 2004 Indian Ocean Tsunami

The devastating 2004 Indian Ocean tsunami caught millions of coastal residents and the scientific community off-guard. Subsequent research in the Indian Ocean basin has identified prehistoric tsunamis, but the timing and recurrence intervals of such events are uncertain. Here we present an extraordinary 7,400 year stratigraphic sequence of prehistoric tsunami deposits from a coastal cave in Aceh, Indonesia. This record demonstrates that at least 11 prehistoric tsunamis struck the Aceh coast between 7,400 and 2,900 years ago. The average time period between tsunamis is about 450 years with intervals ranging from a long, dormant period of over 2,000 years, to multiple tsunamis within the span of a century. Although there is evidence that the likelihood of another tsunamigenic earthquake in Aceh province is high, these variable recurrence intervals suggest that long dormant periods may follow Sunda megathrust ruptures as large as that of the 2004 Indian Ocean tsunami