Amplification of ground motion and waveform complexity in fault zones: examples from the San Andreas and Calaveras Faults   总被引：2，自引：0，他引：2  

V. F. Cormier  P. Spudich 《Geophysical Journal International》1984,79(1):135-152

Summary. P -wave seismograms at ranges less than 10 km are synthesized by asymptotic ray theory and by summation of Gaussian beams for point sources located in a low-velocity wedge surrounding a fault. The computations are performed using models of the wedge inferred from the analysis of reflection and refraction experiments across the San Andreas and Hayward-Calaveras faults. Calculations in these models show that the 10–20Hz vertical displacements of earthquakes located at 3–10km depth are amplified by up to an order of magnitude in a 1–2km wide region centred on the fault trace compared to displacements predicted by laterally homogeneous models of the crust. This amplification is not cancelled by high attentuation in the fault zone and compensates for the reduction in amplitudes directly above the source predicted from the radiation pattern of a strike-slip earthquake. Depending on the source depth of the earthquake and the structure and velocity contrast of the wedge, multiple triplications in the travel-time curve of direct P - and S -waves will occur at stations in the fault zone. A wedge model successfully predicts the triplications observed in the P waveforms of aftershocks of the Coyote Lake earthquake recorded in the fault zone, showing that body waves from microearthquakes can be used to determine the three-dimensional velocity structure of the fault zone. The amplification, waveform complexity, and distortion of ray paths introduced by the low- velocity wedge suggest that its effects should be included in the interpretation of strong ground motions and travel times observed in the fault zone. For realistic models of the wedge, asymptotically approximate methods of calculating the body waveforms are strictly valid for frequencies greater than 20Hz. Numerical methods may be necessary to calculate accurately the wavefield at lower frequencies.  相似文献   

Frequency dependence of Q in the mantle underlying the shield areas of Eurasia, Part II: analyses of long period data     

Alison C. Lees  Zoltan A. Der  Vernon F. Cormier  Margaret E. Marshall  James A. Burnetti 《Geophysical Journal International》1986,87(3):1085-1101

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Use of Multiple Chemical Tracers to Define Habitat Use of Indo-Pacific Mangrove Crab, <Emphasis Type="Italic">Scylla Serrata</Emphasis> (Decapoda: Portunidae)     

Amanda W. J. Demopoulos  Nicole Cormier  Katherine C. Ewel  Brian Fry 《Estuaries and Coasts》2008,31(2):371-381

The mangrove or mud crab, Scylla serrata, is an important component of mangrove fisheries throughout the Indo-Pacific. Understanding crab diets and habitat use should assist in managing these fisheries and could provide additional justification for conservation of the mangrove ecosystem itself. We used multiple chemical tracers to test whether crab movements were restricted to local mangrove forests, or extended to include adjacent seagrass beds and reef flats. We sampled three mangrove forests on the island of Kosrae in the Federated States of Micronesia at Lelu Harbor, Okat River, and Utwe tidal channel. Samples of S. serrata and likely food sources were analyzed for stable carbon (δ¹³C), nitrogen (δ¹⁵N), and sulfur (δ³⁴S) isotopes. Scylla serrata tissues also were analyzed for phosphorus (P), cations (K, Ca, Mg, Na), and trace elements (Mn, Fe, Cu, Zn, and B). Discriminant analysis indicated that at least 87% of the crabs remain in each site as distinct populations. Crab stable isotope values indicated potential differences in habitat use within estuaries. Values for δ¹³C and δ³⁴S in crabs from Okat and Utwe were low and similar to values expected from animals feeding within mangrove forests, e.g., feeding on infauna that had average δ¹³C values near −26.5‰. In contrast, crabs from Lelu had higher δ¹³C and δ³⁴S values, with average values of −21.8 and 7.8‰, respectively. These higher isotope values are consistent with increased crab foraging on reef flats and seagrasses. Given that S. serrata have been observed feeding on adjacent reef and seagrass environments on Kosrae, it is likely that they move in and out of the mangroves for feeding. Isotope mixing model results support these conclusions, with the greatest mangrove ecosystem contribution to S. serrata diet occurring in the largest mangrove forests. Conserving larger island mangrove forests (> 1 km deep) appears to support crab foraging activities.  相似文献   

Nitrogen and water bubbles, oxygen isotopes, shock effects: Deciphering the history of the Bencubbin meteorite breccia     

Claude Perron  Christine Fiéni  Nicole Guilhaumou 《Geochimica et cosmochimica acta》2008,72(3):959-977

We have observed vesicles filled with heavy nitrogen gas and water vapor in three settings in the Bencubbin CB chondrite: in the mesostasis of the silicate clasts, in the mesostasis of the chondrules of an ordinary chondrite (OC) xenolith, and in grains we refer to as bubble grains, and interpret as remelted OC chondrule mesostasis. In our view, these bubbles are a local phenomenon and formed as a consequence of the impact of the OC fragment onto the Bencubbin parent body. The heavy nitrogen in the bubbles came from one or several of its carrier phases in Bencubbin, and the water came from hydrous silicates. As formulated by Meibom et al. (Meibom A., Righter K., Chabot N., Dehn G., Antignano A., McCoy T. J., Krot A. N., Zolensky M. E., Petaev M. I. and Keil K. (2005) Shock melts in QUE 94411, Hammadah al Hamra 237, and Bencubbin: remains of the missing matrix? Meteorit. Planet. Sci.40, 1377-1391) these hydrous phases, similar to the hydrated clasts now found in CH and CB_b chondrites, were probably common in the Bencubbin parent body at that time. They were later almost totally destroyed by a large scale shock event, and contributed to form the impact melt that now fills space in between the large clasts of Bencubbin. Our observations indirectly confirm this hypothesis. From our composition measurements, we infer that the silicate part of the impact melt was made in roughly equal proportions of melted phyllosilicates and melted anhydrous silicates. The oxygen isotopic composition of the impact melt is much heavier than that of the silicate clasts, probably reflecting the composition of the water at the origin of the phyllosilicates. The O isotope measurements of the OC inclusion chondrules present some features that seem to be common in OCs: a composition of the chondrule crystals slightly lighter than that of whole chondrules, and one olivine crystal with a very light composition.  相似文献   

Interaction between different water bodies in a small catchment in the Paris basin (Brévilles,France): Tracing of multiple Sr sources through Sr isotopes coupled with Mg/Sr and Ca/Sr ratios     

Agnès Brenot  Nicole BaranEmmanuelle Petelet-Giraud  Philippe Négrel 《Applied Geochemistry》2008

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Modeling Nonprofit Resilience in Long-Term Recovery in Christchurch,New Zealand     

Nicole S. Hutton  Graham A. Tobin  Linda M. Whiteford 《The Professional geographer》2016,68(4):603-612

Following the 2010–2011 earthquakes in Christchurch, New Zealand, many nonprofit organizations changed or expanded services to address emergent or compounded risks. This research is based on interviews with thirty local community nonprofit managers and discussions with five staff focus groups conducted in 2014. Preexisting nonprofits with flexible organizational structures and emergent nonprofits succeeded in providing services during the emergency response and early recovery phases; nonprofits contracted with the government were better suited for long-term recovery. Shared resources among nonprofit agency connections contributed to successful transitions from response to recovery. Similar organizational resilience factors might occur in other major cities following disasters.  相似文献   

Effects of Recent Instability on Cultivated Area Along the Euphrates River in Iraq     

Glen R. Gibson  Nicole L. Taylor  Nolan C. Lamo  Jason K. Lackey 《The Professional geographer》2017,69(2):163-176

We used MODIS NDVI data to determine whether there was a significant change in cultivated area along the Euphrates River in Iraq after the Iraq War compared to before and during the war. Results revealed that mean cultivated area was largest during the pre–Iraq War period (2000–2003) with 99,115 Mha, reduced some during the early Iraq War period (2003–2006) to 83,480 Mha, reduced even further during the late Iraq War period (2007–2011) to 53,813 Mha due to drought, and increased slightly during the post–Iraq War period (2012–2015) to 69,161 Mha, although not returning to previous highs of the pre–Iraq War or early Iraq War periods. Statistical analysis with the Kruskal–Wallis test revealed that the small cultivated area during the post–Iraq War period was more closely related to the late Iraq War and drought period than previous periods, indicating that recent instability, such as political turmoil following the departure of U.S. troops, violent militant extremism, lack of economic investment, and environmental degradation, has had a similar effect on cultivated area as a devastating drought.  相似文献   

Mud volcanoes and gas vents in the Okhotsk Sea area   总被引：5，自引：0，他引：5  

Shakirov  Renat  Obzhirov  Anatoly  Suess  Erwin  Salyuk  Anatoly  Biebow  Nicole 《Geo-Marine Letters》2004,24(3):140-149

Gas emissions from mud volcanoes on Sakhalin Island and water-column gas flares arising from cold seeps in the Okhotsk Sea appear to be related. They are likely activated by tectonic movements along the transform plate boundary separating the Okhotsk Sea Plate from the Eurasian and Amur plates. Gas vents (flares) and methane anomalies occur in the waters offshore Sakhalin Island, along with NE-SW-trending mounds and fluid escape structures on the seafloor. The intersection of the NE-striking transverse faults on land with the Central Sakhalin and Hokkaido-Sakhalin shear zones apparently determines the sites of mud volcanoes, a pattern that continues offshore where the intersection with the East Sakhalin and West Derugin shear zones determines the sites of the submarine gas vents.  相似文献   

A simple derivation of capture probabilities for the J+1:J and J+2:J orbit-orbit resonance problems     

Nicole Borderies  Peter Goldreich 《Celestial Mechanics and Dynamical Astronomy》1984,32(2):127-136

We present a simplified analytic derivation of the capture probabilities for the j+1j and j+2j orbital resonances. We apply Henrard's method which is based on an extension of the theory of adiabatic invariants and recover the results originally obtained by Yoder.Contribution number 3874 from the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, U.S.A.  相似文献   

A phytoplankton class-specific primary production model applied to the Kerguelen Islands region (Southern Ocean)     

Julia Uitz  Hervé Claustre  F. Brian Griffiths  Joséphine Ras  Nicole Garcia  Valérie Sandroni 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(4):541-560

As part of the KErguelen: compared study of the Ocean and the Plateau in Surface water (KEOPS) project in late summer 2005, we examine the phytoplankton community composition and associated primary production in the waters surrounding the Kerguelen Archipelago, with the emphasis on two contrasted environments: (i) the Kerguelen Plateau, where a large bloom occurs annually, and (ii) the high-nutrient low-chlorophyll (HNLC) offshore waters. A biomarker pigment approach was used to assess the community composition in terms of chlorophyll biomass of three phytoplankton size classes, namely micro-, nano-, and picophytoplankton. The second objective was to evaluate a global class-specific approach for estimating the contribution of the three pigment-based size classes to the primary production in the study area. To do so, primary production rates associated with each phytoplankton class were computed from the class-specific chlorophyll biomass coupled to a class-specific primary production model, and compared with in situ measurements of size-fractionated ¹³C-based primary production. The iron-enriched bloom region was dominated by microphytoplankton (diatoms), which contributed 80–90% to the total primary production (of ≈1 g C m^?2 d^?1). In the HNLC area, the primary production was about 0.30 g C m^?2 d^?1, mainly (65%) achieved by small diatoms and nanoflagellates. The model results show a good overall agreement between predicted and measured total primary production rates. In terms of size classes, agreements were higher for the bloom region than for the HNLC waters. Discrepancies in this complex iron-limited area may be explained essentially by the smaller size of diatoms, or a different set of photophysiological properties.  相似文献