Shallow seismicity, triggered seismicity, and ambient noise tomography at the long-dormant Uturuncu Volcano, Bolivia     

Jennifer A. Jay  Matthew E. Pritchard  Michael E. West  Douglas Christensen  Matthew Haney  Estela Minaya  Mayel Sunagua  Stephen R. McNutt  Mario Zabala 《Bulletin of Volcanology》2012,74(4):817-837

Using a network of 15 seismometers around the inflating Uturuncu Volcano from April 2009 to 2010, we find an average rate of about three local volcano-tectonic earthquakes per day, and swarms of 5–60 events a few times per month with local magnitudes ranging from −1.2 to 3.7. The earthquake depths are near sea level, more than 10 km above the geodetically inferred inflation source and the Altiplano Puna Magma Body. The Mw 8.8 Maule earthquake on 27 February 2010 triggered hundreds of earthquakes at Uturuncu with the onset of the Love and Rayleigh waves and again with the passage of the X2/X3 overtone phases of Rayleigh waves. This is one of the first incidences in which triggering has been observed from multiple surface wave trains. The earthquakes are oriented NW–SE similar to the regional faults and lineaments. The b value of the catalog is 0.49, consistent with a tectonic origin of the earthquakes. We perform ambient noise tomography using Love wave cross-correlations to image a low-velocity zone at 1.9 to 3.9 km depth below the surface centered slightly north of the summit. The low velocities are perhaps related to the hydrothermal system and the low-velocity zone is spatially correlated with earthquake locations. The earthquake rate appears to vary with time—a seismic deployment from 1996 to 1997 reveals 1–5 earthquakes per day, whereas 60 events/day were seen during 5 days using one seismometer in 2003. However, differences in analysis methods and magnitudes of completeness do not allow direct comparison of these seismicity rates. The rate of seismic activity at Uturuncu is higher than at other well-monitored inflating volcanoes during periods of repose. The frequent swarms and triggered earthquakes suggest the hydrothermal system is metastable.  相似文献   

One-year along-beach variation in the maximum depth of erosion resulting from irregular shoreline morphology     

Antonio B. Rodriguez  Patricia L. Rodriguez  Stephen R. Fegley 《Marine Geology》2012

Beach erosion and accretion occur across multiple time scales. Over long time scales (decades to millennia) the shoreface ravinement surface, which is recognized as a coarse lag deposit, forms at the shoreface toe as a result of wave- and current-induced erosion during shoreline transgression. Over short time scales (hours to days) the depth of sediment disturbance, which is recognized as coarse lamina and measured at the foreshore by devices and monitoring tracer beds, forms as a result of wave- and current-induced reworking during a tidal cycle. The maximum depth of erosion (MDOE), quantified here over 1 year, is modulated by processes that operate over a time scale that is between the drivers of short-term (e.g. tides and waves) and long-term (e.g. sea-level rise) beach erosion. The MDOE integrates the erosion that occurs over a discrete time interval and records the maximum depth of erosion that is likely principally induced by storms, which is difficult to quantify by other methods that rely on discrete observations (e.g. changes in elevation or movement of the mean high-water line). A novel technique for quantifying the MDOE, based on comparing the bedding and stratigraphy between cores collected at the same locations over a discrete time interval, is presented here and applied at Onslow Beach, NC, USA. This 12 km-long barrier island has irregular shoreline morphology, characterized by two embayments separated by a central headland. This shape is largely the result of variations in the depth of underlying rock strata and produces a steeper beachface at the headland than at the embayments. At each of the six sites examined along the barrier, the MDOE is found to increase from the backshore to the middle intertidal zone and is higher at the sites closer to the headland. These variations in the MDOE are likely due to the increase in average wave energy impacting the beachface from an offshore direction and steeper beaches (intermediate beach state) at the headland. Where the MDOE is within the beach facies, it is not associated with a coarsening, which is due to the heterolithic nature of the Onslow-beach strata. Where the MDOE is the contact between back-barrier and beach facies it is always associated with a coarsening and a gravel-rich lag deposit because in this case, the MDOE is an amalgamation of multiple erosional events, which is similar to the shoreface ravinement surface. Along-beach variation in the MDOE does not correspond with discrete observations of beach change over the same period and is likely a better indicator of erosion potential than long-term discrete observations, such as changes in surface elevation or the position of the mean high-water line.  相似文献   

Classifying levels of protection in Marine Protected Areas   总被引：1，自引：0，他引：1  

Dalal Al-Abdulrazzak  Stephen C. Trombulak 《Marine Policy》2012,36(3):576-582

Marine Protected Areas (MPAs) are an important tool for the conservation of marine species and ecosystems. Yet despite the significant differences between marine and terrestrial systems in terms of their critical ecological processes, stresses, and relationships with cultural systems, methods used to characterize levels of protection for biological diversity in MPAs are all derived from schemes developed for terrestrial systems. A new system designed to classify levels of protection in MPAs is proposed, based on criteria specifically relevant to marine systems. MPAs are characterized by each of the seven criteria: designated use, quality of natural character, extent of protection throughout the year, extent of zoning into sub-areas for multiple uses, public access, extraction of resources, and size with respect to supporting critical ecological processes. Five levels of protection are defined, labeled I-V: Wilderness Management Area (Level I), Research Management Area, Ecological Management Area, Human Recreation Management Area, and Sustainable Resource Management Area (V). A level is assigned to an MPA based on the level that matches the largest number of categories across all seven criteria. The uses and benefits of this system of classification relative to existing systems are discussed and examples of its application are illustrated using data on 83 MPAs in California (USA) and 10 globally.  相似文献   

The influence of a season of extreme wet weather events on exposure of the World Heritage Area Great Barrier Reef to pesticides     

Kennedy K  Devlin M  Bentley C  Lee-Chue K  Paxman C  Carter S  Lewis SE  Brodie J  Guy E  Vardy S  Martin KC  Jones A  Packett R  Mueller JF 《Marine pollution bulletin》2012,64(7):1495-1507

The 2010-2011 wet season was one of extreme weather for the State of Queensland, Australia. Major rivers adjacent to the Great Barrier Reef (GBR) were discharging at rates 1.5 to >3 times higher than their long term median. Exposure to photosystem II herbicides has been routinely monitored over a period of up to 5 years at 12 inshore GBR sites. The influence of this wet season on exposure to photosystem II herbicides was examined in the context of this long-term monitoring record and during flood plume events in specific regions. Median exposures expressed as diuron equivalent concentration were an average factor of 2.3 times higher but mostly not significantly different (p<0.05) to the median for the long-term monitoring record. The herbicides metolachlor and tebuthiuron were frequently detected in flood plume waters at concentrations that reached or exceeded relevant water quality guidelines (by up to 4.5 times).  相似文献   

Analytical Solutions Involving Shock Waves for Testing Debris Avalanche Numerical Models     

Sudi Mungkasi  Stephen Gwyn Roberts 《Pure and Applied Geophysics》2012,169(10):1847-1858

Analytical solutions to debris avalanche problems involving shock waves are derived. The debris avalanche problems are described in two different coordinate systems, namely, the standard Cartesian and topography-linked coordinate systems. The analytical solutions can then be used to test debris avalanche numerical models. In this article, finite volume methods are applied as the numerical models. We compare the performance of the finite volume method with reconstruction of the conserved quantities based on stage, height, and velocity to that of the conserved quantities based on stage, height, and momentum for solving the debris avalanche problems involving shock waves. The numerical solutions agree with the analytical solution. In addition, both reconstructions lead to similar numerical results. This article is an extension of the work of Mangeney et al. (Pure Appl Geophys 157(6–8):1081–1096, 2000).  相似文献   

Experimental and analytical study of the bi‐directional behavior of the triple friction pendulum isolator     

Tracy C. Becker  Stephen A. Mahin 《地震工程与结构动力学》2012,41(3):355-373

This paper presents a non‐linear, kinematic model for triple friction pendulum isolation bearings. The model, which incorporates coupled plasticity and circular restraining surfaces for all sliding surfaces, is capable of capturing bi‐directional behavior and is able to explicitly track the movement of each internal component. The model is general so that no conditions regarding bearing properties, which effect the sequence of sliding stages, are required for the validity of the model. Controlled‐displacement and seismic‐input experiments were conducted using the shake table at the University of California, Berkeley to assess the fidelity of the proposed model under bi‐directional motion. Comparison of the experimental data with the corresponding results of the kinematic model shows good agreement. Additionally, experiments showed that the performance of TFP bearings is reliable over many motions, and the behavior is repeatable even when initial slider offsets are present. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Multitemporal ALSM change detection,sediment delivery,and process mapping at an active earthflow   总被引：1，自引：0，他引：1  

Stephen B. DeLong  Carol S. Prentice  George E. Hilley  Yael Ebert 《地球表面变化过程与地形》2012,37(3):262-272

Remote mapping and measurement of surface processes at high spatial resolution is among the frontiers in Earth surface process research. Remote measurements that allow meter‐scale mapping of landforms and quantification of landscape change can revolutionize the study of landscape evolution on human timescales. At Mill Gulch in northern California, USA, an active earthflow was surveyed in 2003 and 2007 by airborne laser swath mapping (ALSM), enabling meter‐scale quantification of landscape change. We calculate four‐year volumetric flux from the earthflow and compare it to long‐term catchment average erosion rates from cosmogenic radionuclide inventories from adjacent watersheds. We also present detailed maps of changing features on the earthflow, from which we can derive velocity estimates and infer dominant process. These measurements rely on proper digital elevation model (DEM) generation and a simple surface‐matching technique to align the multitemporal data in a manner that eliminates systematic error in either dataset. The mean surface elevation of the earthflow and an opposite slope that was directly influenced by the earthflow decreased 14 ± 1 mm/yr from 2003 to 2007. By making the conservative assumption that these features were the dominant contributor of sediment flux from the entire Mill Gulch drainage basin during this time interval, we calculate a minimum catchment‐averaged erosion rate of 0·30 ± 0·02 mm/yr. Analysis of beryllium‐10 (¹⁰Be) concentrations in fluvial sand from nearby Russian Gulch and the South Fork Gualala River provide catchment averaged erosion rates of 0·21 ± 0·04 and 0·23 ± 0·03 mm/yr respectively. From translated landscape features, we can infer surface velocities ranging from 0·5 m/yr in the wide upper ‘source’ portion of the flow to 5 m/yr in the narrow middle ‘transport’ portion of the flow. This study re‐affirms the importance of mass wasting processes in the sediment budgets of uplifting weak lithologies. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Creating a greater partnership: analysing partnership in the Catholic Church development chain     

Stephen Morse  Nora McNamara 《Area》2008,40(1):65-78

This paper presents results from a project designed to explore the meaning and function of partnership within the Catholic Church development chain. The geography literature has had little to say about such aid chains, especially those founded on faith-based groups. The relationships between three Catholic Church-based donors – referred to as A, B and C – with development personnel of the diocese of the Abuja Ecclesiastical Province (AEP) as well as other Catholic Church structures in Nigeria were analysed. The aim was to explore the forces behind the relationships and how 'patchy' these relationships were in AEP. Respondents were asked to give each of the donors a score in relation to four questions covering their relationship with the donors. Results suggest that the modus operandi of donor 'A' allows it to be perceived as the 'best' partner, while 'B' was scored less favourably because of a perception that it attempts to act independently of existing structures in Nigeria rather than work through them. There was significant variation between diocese in this regard, as well as between the diocese and other structures of the Church (Provinces, Inter-Provinces and National Secretariat). Thus 'partnership' in the Catholic Church aid chain is a highly complex, contested and 'visioned' term and the development of an analytical framework has to take account of these fundamentals.  相似文献   

The evolution of stellar mass and the implied star formation history     

Stephen M. Wilkins  Neil Trentham  Andrew M. Hopkins 《Monthly notices of the Royal Astronomical Society》2008,385(2):687-694

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Global Detection of Infrasonic Signals from Three Large Bolides     

Stephen J. Arrowsmith  Doug ReVelle  Wayne Edwards  Peter Brown 《Earth, Moon, and Planets》2008,102(1-4):357-363

We present the infrasonic observations of three large bolides that were observed at numerous International Monitoring System (IMS) infrasound arrays on a global scale. First, a simple procedure for the global association of infrasound detections from large infrasound events is outlined. Infrasound signals are associated with large events based on arrival time, backazimuth and uniqueness at a given IMS array. Next, we apply the algorithm to three bolides and investigate some of the factors affecting the detectability of infrasound from large events. Our findings suggest that site-noise effects significantly degrade the capability of the IMS infrasound network, suggesting that more effort is required to reduce ambient site noise. These results have implications for the use of infrasound measurements (in particular those from IMS stations) as a tool for evaluating the global flux of near-Earth objects.  相似文献