Performance of the Italian strong motion network during the 2009, L��Aquila seismic sequence (central Italy)     

Elisa Zambonelli  Rita de Nardis  Luisa Filippi  Mario Nicoletti  Mauro Dolce 《Bulletin of Earthquake Engineering》2011,9(1):39-65

On April 6, 2009, the town of L’Aquila in the Abruzzo region (central Italy) was struck by a seismic event at 01:32 (UTC), of magnitude M_W = 6.3. The mainshock was followed by a long period of intense seismic activity and within seven days after the mainshock there were seven events of magnitude M_W ≥ 5 that occurred from April 6 to April 13. This long seismic sequence was characterized by a complex rupture mechanism that involved two major normal faults of the central Apennines: the Paganica and the Gorzano faults. The strong-motions of the mainshock were recorded by 64 stations of the Italian Strong-motion Network (RAN) operated by the National Civil Protection Department (DPC). Six stations of a local strong-motion array were working in NW L’Aquila suburb area. One of them, located at about 6 km from the Paganica fault surface tip-line, set up in trigger mode, recorded continuously for more than 20 min the mainshock and the aftershocks. Besides the mainshock, the RAN stations recorded in total 78 foreshocks and aftershocks of M_L ≥ 3.5, during the period from January to December 2009. The corresponding waveforms provide the most extensive digital strong ground motion data set ever recorded in Italy. Moreover, the 48 three-component observations of events of magnitude M_W ≥ 5, recorded at a distance less than 15 km from each of the major involved faults, provide a significant increasing of near-field records available for the Italian territory. Six days after the mainshock, the strong-motion dataset, referred to preliminary locations of the events with M_L ≥ 4.0, was made available on the DPC web site () and at the same time it was delivered to the ITACA database (). This dataset has been used by many authors in scientific papers and by engineers, geophysicists and geologists for professional technical works. In this paper, the present-day available strong-motion signals from the L’Aquila sequence and the performance of the Italian strong-motion network in terms of the number and quality of recorded data, the geometry and data transmission system are described. In addition the role of the temporary network that represents an extension of the permanent Italian strong-motion network, supporting the emergency response by civil protection authorities and improving the network coverage has been evaluated.  相似文献   

Plant Cover,Herbivory, and Resiliency in a Cape Cod Salt Marsh: Multi-year Responses and Recovery Following Manipulation of Nutrients and Competition     

Carol S. Rietsma  Rita Oliveira Monteiro  Ivan Valiela 《Estuaries and Coasts》2011,34(1):198-210

To assess responses and recovery of salt marsh grass species, we manipulated external nutrient supply and removed shoots of Spartina alterniflora or Spartina patens from fertilized and control plots in a Massachusetts marsh. The pulse-and-recovery experiment included treatments for 5 years, and recovery for an additional 7 years. Responses of these potential competitors sensitively depended on local contingencies of elevation and nutrient dose, and, moreover, the differences in outcomes were emphasized at longer time scales. Local contingencies became manifest as differences in responsiveness and resiliency of the different grass species, with differing time courses and longer-term outcomes as to what species were present. These features might explain the diverse results obtained in shorter-term salt marsh experiments, and provide a view of the complex suite of species-specific and external environmental variables that may control competitive interactions in general.  相似文献   

Assessing Nitrogen Dynamics Throughout the Estuarine Landscape     

Ashley R. Smyth  Suzanne P. Thompson  Kaylyn N. Siporin  Wayne S. Gardner  Mark J. McCarthy  Michael F. Piehler 《Estuaries and Coasts》2013,36(1):44-55

Assessing nitrogen dynamics in the estuarine landscape is challenging given the unique effects of individual habitats on nitrogen dynamics. We measured net N₂ fluxes, sediment oxygen demand, and fluxes of ammonium and nitrate seasonally from five major estuarine habitats: salt marshes, seagrass beds (SAV), oyster reefs, and intertidal and subtidal flats. Net N₂ fluxes ranged from 332?±?116 μmol?N-N₂?m^?2?h^?1 from oyster reef sediments in the summer to ?67?±?4 μmol?N-N₂?m^?2?h^?1 from SAV in the winter. Oyster reef sediments had the highest rate of N₂ production of all habitats. Dissimilatory nitrate reduction to ammonium (DNRA) was measured during the summer and winter. DNRA was low during the winter and ranged from 4.5?±?3.0 in subtidal flats to 104?±?34 μmol?¹⁵NH ₄ ⁺ ?m^?2?h^?1 in oyster reefs during the summer. Annual denitrification, accounting for seasonal differences in inundation and light, ranged from 161.1?±?19.2 mmol?N-N₂?m^?2?year^?1 for marsh sediments to 509.9?±?122.7 mmol?N-N₂?m^?2?year^?1 for SAV sediments. Given the current habitat distribution in our study system, an estimated 28.3?×?10⁶?mol of N are removed per year or 76 % of estimated watershed nitrogen load. These results indicate that changes in the area and distribution of habitats in the estuarine landscape will impact ecosystem function and services.  相似文献   

Volcanic tsunamis and prehistoric cultural transitions in Cook Inlet,Alaska     

James Begét  Cynthia Gardner  Kathleen Davis 《Journal of Volcanology and Geothermal Research》2008

The 1883 eruption of Augustine Volcano produced a tsunami when a debris avalanche traveled into the waters of Cook Inlet. Older debris avalanches and coeval paleotsunami deposits from sites around Cook Inlet record several older volcanic tsunamis. A debris avalanche into the sea on the west side of Augustine Island ca. 450 years ago produced a wave that affected areas 17 m above high tide on Augustine Island. A large volcanic tsunami was generated by a debris avalanche on the east side of Augustine Island ca. 1600 yr BP, and affected areas more than 7 m above high tide at distances of 80 km from the volcano on the Kenai Peninsula. A tsunami deposit dated to ca. 3600 yr BP is tentatively correlated with a southward directed collapse of the summit of Redoubt Volcano, although little is known about the magnitude of the tsunami. The 1600 yr BP tsunami from Augustine Volcano occurred about the same time as the collapse of the well-developed Kachemak culture in the southern Cook Inlet area, suggesting a link between volcanic tsunamis and prehistoric cultural changes in this region of Alaska.  相似文献   

New constraints on the HIMU mantle from neon and helium isotopic compositions of basalts from the Cook–Austral Islands     

Rita Parai  Sujoy Mukhopadhyay  John C. Lassiter 《Earth and Planetary Science Letters》2009,277(1-2):253-261

High ⁴He/³He ratios of 100 000 to 160 000 found at HIMU ocean islands (“high μ,” where μ is the U/Pb ratio) are usually attributed to the presence of recycled oceanic crust in the HIMU mantle source. However, significantly higher ⁴He/³He ratios are expected in recycled crust after residence in the mantle for periods greater than 1 Ga. In order to better understand the helium isotopic signatures in HIMU basalts, we have measured helium and neon isotopic compositions in a suite of geochemically well-characterized basalts from the Cook–Austral Islands. We observe ⁴He/³He ratios ranging from 56 000 to 141 000, suggesting the involvement of mantle reservoirs both more and less radiogenic than the mantle source for mid-ocean ridge basalts (MORBs). In addition, we find that the neon isotopic compositions of HIMU lavas extend from the MORB range to compositions less nucleogenic than MORBs. The Cook-Austral HIMU He–Ne isotopic compositions, along with Sr, Nd, Pb, and Os isotopic compositions, indicate that in addition to recycled crust, a relatively undegassed mantle end-member (e.g., FOZO) is involved in the genesis of these basalts. The association of relatively undegassed mantle material with recycled crust provides an explanation for the close geographical association between HIMU lavas and EM (enriched mantle)-type lavas from this island chain: EM-type signatures represent a higher mixing proportion of relatively undegassed mantle material. Mixing between recycled material and relatively undegassed mantle material may be a natural result of entrainment processes and convective stirring in deep mantle.  相似文献   

Time dependence of negative buoyancy and the subduction of continental lithosphere   总被引：1，自引：0，他引：1  

Giorgio Ranalli  Rita Pellegrini  Sergio D&#x;Offizi 《Journal of Geodynamics》2000,30(5)

The time evolution of negative buoyancy of a subducting slab is modelled from the beginning of subduction under various kinematic conditions (dip angle and subduction velocity). The calculations take into account the thermal and density effects of the variations of the thermophysical parameters with temperature and pressure, and of phase transitions. The magnitude of the negative buoyancy increases during subduction of oceanic lithosphere, up to values in the (2–4) × 10¹³ N m⁻¹ range when the tip of the slab reaches a depth of 600–700 km. If continental material arrives at the trench and is subducted, the downward buoyancy decreases by an amount proportional to the volume of the subducted continental crust. Assuming that subduction stops when the buoyancy becomes zero, and that delamination of the continental crust or slab breakoff do not occur, the maximum downdip length of the subductable continental crust is estimated as a function of the dip angle, subduction velocity and geometry of the margin. In most cases, subduction of continental material down to depths of 100–250 km is possible, and continental subduction can continue for times up to 10–15 Ma if the velocity is low. These estimates are not significantly affected by the hypothetical occurrence of a metastable olivine wedge within the slab, and could be lower bounds if the lower continental crust is mafic and transforms to eclogite.  相似文献   

The role of constraints on joint hypocentre determination in seismotectonic studies     

Rodolfo Console  Rita Di Giovambattista  Aldo Di Sanza  Paolo Favali   Giuseppe Smriglio 《Geophysical Journal International》2000,143(1):129-141

In this paper we show how the performance of the joint hypocentre determination (JHD) method can be improved, leading to reduced instability in cases close to singularity. The method has been extended by imposing a number of constraints introduced by other authors, and adding a new one. We tested the stability of the method and the relative advantages of the various constraints by simulating a geometrical space distribution of hypocentres recorded by a regional seismic network. We then applied this method to deep earthquakes that occurred in the Southern Tyrrhenian Sea subduction zone and to the seismicity of the Northern Apennines, which is moderately deeper than the typical shallow seismicity of the Apennines. The results obtained from the analysis of synthetic data and actual earthquakes confirm that the JHD method produces less scatter in the hypocentral determinations with respect to the standard locations. The main conclusion of our study is that we can significantly reduce the systematic mislocations that result from applying JHD to very clustered seismicity if we introduce the appropriate set of constraints.  相似文献   

Long-term effects of a toxic algal bloom on subtidal soft-sediment macroinvertebrate communities in Wellington Harbour, New Zealand   总被引：3，自引：1，他引：2  

Kerstin Krger  Jonathan P.A. Gardner  Ashley A. Rowden  Robert G. Wear 《Estuarine, Coastal and Shelf Science》2006,67(4):589-604

The long-term effects (>1 year) of a naturally occurring toxic plankton bloom (Karenia brevisulcata) on subtidal benthic macroinvertebrate communities were investigated in Wellington Harbour, a semi-enclosed temperate embayment in New Zealand. For 3 years communities were sampled at three different sites in the harbour. Analyses revealed that community recovery following the bloom was site-specific. Multivariate analyses indicated that at one site community composition was approaching recovery 3 years post-bloom. At the second site, a sequential recovery process was indicated, whereas at the third site the community composition oscillated from year to year, but did not show any signs of a sequential recovery process. The nature of the hydrodynamic regime was identified as a major factor influencing the observed recovery processes. Communities exposed to an active hydrodynamic regime were less affected by the bloom and differed little in their composition pre- and post-bloom, as they were naturally in a perpetual state of recovery as indicated by a dominance of r-selected species. The community at the hydrodynamically less active site was more affected by the bloom and exhibited temporal differences in composition consistent with successional models. Complete recovery to a pre-disturbance climax community dominated by K-selected species is likely to take 4–5 years, if not interrupted by other disturbances. Given the increased occurrence of harmful algal blooms worldwide, more monitoring and manipulative studies are needed to further evaluate the effects of such disturbances on macrobenthic communities.  相似文献   

Microlithic sites and their paleoenvironmental setting,Southeast India; a reevaluation     

R. Gardner  H. Martingell 《Geoarchaeology》1990,5(1):1-13

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Effects of forestry on summertime low flows and physical fish habitat in snowmelt‐dominant headwater catchments of the Pacific Northwest     

Stefan Gronsdahl  R. Dan Moore  Jordan Rosenfeld  Rich McCleary  Rita Winkler 《水文研究》2019,33(25):3152-3168

Periods of summertime low flows are often critical for fish. This study quantified the impacts of forest clear‐cutting on summertime low flows and fish habitat and how they evolved through time in two snowmelt‐dominant headwater catchments in the southern interior of British Columbia, Canada. A paired‐catchment analysis was applied to July–September water yield, the number of days each year with flow less than 10% of mean annual discharge, and daily streamflow for each calendar day. The postharvest time series were divided into treatment periods of approximately 6–10 years, which were analysed independently to evaluate how the effects of forestry changed through time. An instream flow assessment using a physical habitat simulation‐style approach was used to relate streamflow to the availability of physical habitat for resident rainbow trout. About two decades after the onset of logging and as the extent of logging increased to approximately 50% of the catchments, reductions in daily summertime low flows became more significant for the July–September yield (43%) and for the analysis by calendar day (11–68%). Reductions in summertime low flows were most pronounced in the catchment with the longest postharvest time series. On the basis of the temporal patterns of response, we hypothesize that the delayed reductions in late‐summer flow represent the combined effects of a persistent advance in snowmelt timing in combination with at least a partial recovery of transpiration and interception loss from the regenerating forests. These results indicate that asymptotic hydrological recovery as time progresses following logging is not suitable for understanding the impacts of forest harvesting on summertime low flows. Additionally, these reductions in streamflow corresponded to persistent decreases in modelled fish habitat availability that typically ranged from 20% to 50% during the summer low‐flow period in one of the catchments, suggesting that forest harvest may have substantial delayed effects on rearing salmonids in headwater streams.  相似文献