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1.
Total nitrogen (TN), total phosphorus (TP), and total suspended solids (TSS) loadings [log (kg ha−1 yr−1)] were regressed against seagrass depth limits (percent of depth-limit targets) to back-predict the load limits or allocations (kg ha−1 yr−1 or kg yr−1) necessary to meet targeted seagrass depth limits in the Indian River and Banana River (IRBR) lagoons, Florida. Because the load allocations can be applied as total maximum daily loads (TMDL) for the IRBR (U.S. Environmental Protection Agency mandate), the method and results are developed and presented toward that end. The regression analyses indicate that the range of surface-discharge load limits (nonpoint + point source), per watershed area, required to achieve the desired depth limits for seagrass in the IRBR are approximately 2.4–3.2 kg ha−1 yr−1 TN, 0.41–0.64 kg ha−1 yr−1 TP, and 48–64 kg ha−1 yr−1 TSS. This simple regression method may have application to other shallow estuarine lagoons or bays where seagrass growth is limited by light and water transparency, water transparency is strongly affected by watershed pollutant loadings, water residence times are sufficiently long to allow seagrass coverage to respond to and covary with total load inputs, and multiyear monitoring has yielded sufficient variability in both pollutant loadings and seagrass coverages to develop a statistically meaningful relationship.  相似文献   

2.
Undulating landscapes of Chhotanagpur plateau of the Indian state of Jharkhand suffer from soil erosion vulnerability of varying degrees. An investigation was undertaken in some sections of the Upper Subarnarekha River Basin falling within this state. An empirical equation known as Universal Soil Loss Equation (USLE) was utilized for estimating the soil loss. Analysis of remote sensing satellite data, digital elevation model (DEM) and geographical information system (GIS)–based geospatial approach together with USLE led to the soil erosion assessment. Erosion vulnerability assessment was performed by analyzing raster grids of topography acquired from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global DEM data. LANDSAT TM and ETM+ satellite data of March 2001 and March 2011 were used for inferring the land use–land cover characteristics of the watershed for these years, respectively. USLE equation was computed within the GIS framework to derive annual soil erosion rates and also the areas with varying degrees of erosion vulnerability. Erosion vulnerability units thus identified covered five severity classes of erosion ranging from very low (0–5 ton ha?1 yr?1) to very severe (> 40 ton ha?1 yr?1). Results indicated an overall increase of erosion in the year 2011 as compared to the erosion computed for the year 2001. Maximum soil erosion rate during the year 2001 was found up to 40 ton ha?1 yr?1, whereas this went up to 49.80 ton ha?1 yr?1 for the year 2011. Factors for the increase in overall erosion could be variation in rainfall, decrease in vegetation or protective land covers and most important but not limited to the increase in built-up or impervious areas as well.  相似文献   

3.
Experimental data refer to a preliminary estimate of suspended solid and solute load of a perennial river. The basin is composed almost entirely of bare mesozoic, highly fractured, karstified carbonate rocks of the central Apennine range. The suspended solid load related to stormflow events in 1991 corresponds to about 14,970 t yr–1. For the same period the solute load is 60,060 t yr–1 for a mean base flow discharge of 9.4 m3 s–1. Based on the mean concentration of Ca + Mg in water, the value of dissolution of carbonate rocks of 37.1 m3 km–2 (equivalent approximately to 0.04 mm yr–1) was calculated. Physical and chemical variations that occur during storm events indicate the complex dynamic processes in the karst aquifer and the role undertaken by the epikarst as perched water reservoir and by the major conduits that develop through the vadose and saturated zones of the karst system.  相似文献   

4.
Pond water in intensive shrimp ponds is typically high in nutrients, solids, and BOD and may have an adverse environmental impact when discharged to natural waters. As part of ongoing research to develop intensive production technologies that minimize the potential for environmental impact, a study investigated the effect of lowrate, coarse-grain sand filtration on the quality of effluent being discharged from an intensive shrimp pond receiving 5% d?1 water exchange. The effect of sand filtration on a recirculating no-exchange pond was also examined. For comparison, a third pond received no water exchange and no filtration. Sand filtration removed some particulate matter, but levels of dissolved and particulate organic and inorganic nutrients were changed little and were sometimes higher as the result of in situ decomposition. Low-rate sand filtration is not seen as a cost-effective method of increasing the carrying capacity of no-exchange shrimp ponds or drastically improving the effluent quality of ponds with water exchange. Compared to previous studies with decreased or no water exchange, the application of feed in these ponds was more stable with small portions fed at frequent intervals with a constant rate of 80 kg ha?1 d?1. These ponds, stocked with 40 m?2 juvenilePenaeus vannamei, had excellent survival and normal growth, resulting in productions levels approaching 7,000 kg ha?1 crop?1 without water exchange. This indicates that intensive shrimp farming may be possible in static no-exchange systems, thereby minimizing the potential impact of effluent as long as feed inputs do not overwhelm the assimilative capacity of the pond ecosystem. *** DIRECT SUPPORT *** A01BY069 00011  相似文献   

5.
 Three dolines (sinkholes), each representing different land uses (crop, grass, and forest) in a karst area in East Tennesse, were selected to determine soil erosional and depositional rates. Three methods were used to estimate the rates: fallout radiocesium (137Cs) redistribution, buried surface soil horizons (Ab horizon), and the revised universal soil loss equation (RUSLE). When 137Cs redistribution was examined, the average soil erosion rates were calculated to be 27 t ha–1 yr–1 at the cropland, 3 t ha–1 yr–1 at the grassland, and 2 t ha–1 yr–1 at the forest. By comparison, cropland erosion rate of 2.6 t ha–1 yr–1, a grassland rate of 0.6 t ha–1 yr–1, and a forest rate of 0.2 t ha–1 yr–1 were estimated by RUSLE. The 137Cs method expressed higher rates than RUSLE because RUSLE tends to overestimate low erosion rates and does not account for deposition. The buried surface horizons method resulted in deposition rates that were 8 t ha–1 yr–1 (during 480 yr) at the cropland, 12 t ha–1 yr–1 (during 980 yr) at the grassland, and 4 t ha–1 yr–1 (during 101 yr) at the forest site. By examining 137Cs redistribution, soil deposition rates were found to be 23 t ha–1 yr–1 at the cropland, 20 t ha–1 yr–1 at the grassland, and 16 t ha–1 yr–1 at the forest site. The variability in deposition rates was accounted for by temporal differences;137Cs expressed deposition during the last 38 yr, whereas Ab horizons represented deposition during hundreds of years. In most cases, land use affected both erosion and deposition rates – the highest rates of soil redistribution usually representing the cropland and the lowest, the forest. When this was not true, differences in the rates were attributed to differences in the size, shape, and closure of the dolines. Received: 10 October 1995 · Accepted: 13 October 1995  相似文献   

6.
Nitrogen loads into Lemon Bay, Florida were modeled to have increased ca. 59% between pre-development (i.e., 1850) estimates (5.3 kg TN ha−1 yr−1. and estimates for the year 1995 (8.4 kg TN ha−1 yr−1). By the year 2010, nitrogen loads are predicted to increase an additional 45% or 58%, depending upon progress being made toward replacing older septic tank systems with centralized sewerage (nitrogen loads of 12.2 and 13.3 kg TN ha−1 yr−1, respectively). Using 1995 estimates, nonpoint sources (stormwater runoff) are throught to be responsible for ca. 76% of the annual nitrogen load, followed by septic tank systems (14%), rainfall (10%), and an insignificant load from baseflow. Based on an empirically-derived nitrogen load:chlorophylla relationship developed for a portion of nearby Tampa Bay, a 45% increase in nitrogen loads into Lemon Bay could result in a 29% increase in annual average chlorophylla concentrations. Using the estimate of a 29% increase in future chlorophylla concentrations, an empirically-derived optical model for Lemon Bay suggests that light attenuation coefficients in the bay would increase ca. 9%, and the average depth limit ofThalassia testudinum in Lemon Bay would decrease by ca. 24%.  相似文献   

7.
Natural seabed gas seeps as sources of atmospheric methane   总被引：5，自引：0，他引：5  
Microbial and thermogenic methane migrates towards the seabed where some is utilised during microbially-mediated anaerobic oxidation. Excess methane escapes as gas seeps, which occur in a variety of geological contexts in every sea and ocean, from inter-tidal zones to deep ocean trenches. Some seeps are localised, gentle emanations; others are vigorous covering areas of >1 km2; the most prolific seeps reported (offshore Georgia) produce ~40 t CH4 per year. Gas bubbles lose methane to the water as they rise, so deep water seeps are unlikely to contribute to the atmosphere. However, bubbles break the surface above some shallow water seeps. Estimates of the total methane contribution to the atmosphere are poorly constrained, largely because the data set is so small. 20 Tg yr–1 is considered a realistic first approximation. This is a significant contribution to the global budget, particularly as methane from seeps is 14C-depleted. A seep measurement programme is urgently required.GEM  相似文献   

8.
Chemical weathering rates and erosionrates of granitic till in northern Sweden have beenestimated. The present-day chemical weathering rate iscompared with the long-term average weathering ratesince the last deglaciation approximately 8,700 yearsago. Also, the present-day release rates of major andtrace elements due to chemical weathering are comparedwith the mobility of these elements in a spodosolprofile as shown by soil water samples from the vadozezone. The estimation of the past weathering rate isbased on elemental depletion trends in a soil profile(typic haplocryod), whereas the present weatheringrate is based on elemental input/output budgets in asmall catchment (9.4 km2). The long-term averagechemical erosion rate, expressed as the sum of majorelement oxides (SiO2, Al2O3, CaO,Fe2O3, K2O, MgO, MnO, Na2O,P2O5, TiO2), was estimated to be4.9 gm-2 yr-1. The long-term base cation(Ca2+, Mg2+, Na+, K+) depletionwas 0.325 keq ha-1 yr-1. The currentchemical erosion rate was estimated to be2.43.0 g -2 yr-1, which is at least an order ofmagnitude higher than the rate of physical erosion,and the base cation flux due to chemical weathering is0.356–0.553~keq ha-1 yr-1. However,0.074 keq ha-1 yr-1 of this flux may be related tocation exchange processes induced by atmospheric inputof acid rain. There is no evidence for any recentlyincreased weathering rate of silicates in this area.The inputs of Cd, Cu, Ni and Zn exceed the outputs,and hence, these elements are currently accumulatingin the soil.There is a distinct seasonal variation in thechemical composition of the soil water. Results fromthe soil water samples show that Na, followed by Siand S (Cl was not measured), are the most mobileelements in the spodosol profile between the E-horizonand the C-horizon, and that Al and Fe were the leastmobile elements. However, there is no simplerelationship between the mobility of an element in thespodosol profile and the current release rate due toweathering of that element. This fact may haveimplications for the validity of the comparisonbetween the past and present weathering rates asperformed in this study.  相似文献   

9.
The Alaknanda and Bhagirathi Rivers originate in the mountainous regions of the Himalayas (Garhwal) and result in high sediment yields causing flood hazards downstream of the Ganga River and high sediment flux to the Bay of Bengal. The rivers are perennial, since runoff in these rivers is controlled by both precipitation and glacial melt. In the present study, three locations in the upper reaches of the Ganga River were monitored for 1 yr (daily observations of, more than >1000 samples) for suspended sediment concentrations. In addition, more than one hundred samples were collected from various locations of the Alaknanda and Bhagirathi Rivers at different periods to observe spatial and temporal variations in river suspensions. Further, multi-annual data (up to 40 yrs) of water flow and sediment concentrations were used for inferring the variations in water flow and sediment loads on longer time scales. In most previous studies of Himalayan Rivers, there has been a general lack of long term water flow and sediment load data. In the present study, we carried out high frequency sampling, considered long term discharge data and based on these information, discussed the temporal and spatial variations in water discharge and sediment loads in the rivers in the Himalayan region. The results show that, >75% of annual sediment loads are transported during the monsoon season (June through September). The annual physical weathering rates in the Alaknanda and Bhagirathi River basins at Devprayag are estimated to be 863 tons km−2 yr−1 (3.25 mm yr−1) and 907 tons km−2 yr−1 (3.42 mm yr−1) respectively, which are far in excess of the global average of 156 tons km−2 yr−1 (0.58 mm yr−1).  相似文献   

10.
In situ benthic flux chamber experiments were performed during late austral spring and early summer of 1996 at eleven nearshore locations in the southern Patos Lagoon, Brazil. The Patos Lagoon is the largest lagoonal system in South America and is a very important nursery ground for local fin fish and shell fish fisheries. These are the first benthic flux measurements made in Patos Lagoon and they suggest that remineralizationwithin the sediments may dominate the recycling of organic matter and nutrients in thelagoon. Measured oxygen benthic fluxes (45–160 mmol m-2 d-1) are sufficientto remineralize reported mean water column carbon fixation while phosphate and fixednitrogen benthic fluxes (-0.4–2 and -1.1–4.2 mmol m-2 d-1, respectively)are sufficient to supply 100% and 25% of the required water column nutrient demand,respectively. Although of limited areal and temporal coverage, these initial studiesdemonstrate that sediments play a major role in the metabolism and nutrient cyclingwithin the Patos Lagoon Estuary and that future studies of lagoonal biogeochemistrymust consider exchange with the bottom.  相似文献   

11.
The 36Cl dating method is increasingly being used to determine the surface-exposure history of Quaternary landforms. Production rates for the 36Cl isotopic system, a critical component of the dating method, have now been refined using the well-constrained radiocarbon-based deglaciation history of Whidbey and Fidalgo Islands, Washington. The calculated total production rates due to calcium and potassium are 91±5 atoms 36Cl (g Ca)−1 yr−1 and are 228±18 atoms 36Cl (g K)−1 yr−1, respectively. The calculated ground-level secondary neutron production rate in air, Pf(0), inferred from thermal neutron absorption by 35Cl is 762±28 neutrons (g air)−1 yr−1 for samples with low water content (1–2 wt.%). Neutron absorption by serpentinized harzburgite samples of the same exposure age, having higher water content (8–12 wt.%), is 40% greater relative to that for dry samples. These data suggest that existing models do not adequately describe thermalization and capture of neutrons for hydrous rock samples. Calculated 36Cl ages of samples collected from the surfaces of a well-dated dacite flow (10,600–12,800 cal yr B.P.) and three disparate deglaciated localities are consistent with close limiting calibrated 14C ages, thereby supporting the validity of our 36Cl production rates integrated over the last 15,500 cal yr between latitudes of 46.5° and 51°N. Although our production rates are internally consistent and yield reasonable exposure ages for other localities, there nevertheless are significant differences between these production rates and those of other investigators.  相似文献   

12.
Single sample magnetic susceptibility measurements are used to correlate synchronous levels in 16 cores of dated (210Pb, 137Cs) recent sediment taken from the deep and oligotrophic Llyn Peris, N. Wales, in order to provide a basis for calculating total sediment and chemical influx through time. Results show that sediment influx has steadily increased since c. 1750 A.D. to reach peak levels in the period 1966–1976 A.D., equivalent to a rise in erosion in the catchment from c. 5 t km−2 yr−1 to c. 42 t km−2 yr−1. Comparison of down-core susceptibility fluctuations with sediment pollen and organic pigment data indicates that maximum susceptibility values relate to periods of channel erosion and minimum susceptibility values relate to periods of slate debris inwash from spoil tips in the catchment. A study of historical records reveals that pre-twentieth-century peak levels of erosion were due to the effects of extractive industries, while twentieth-century erosion has been caused by overgrazing, increased trampling pressure, and heavy construction works in the catchment.  相似文献   

13.
Breaking the yield frontier of rice   总被引：26，自引：0，他引：26  
Gurdev S. Khush 《GeoJournal》1995,35(3):329-332
Major increases in rice production have occurred during the last 25 years, due to large-scale adoption of high-yielding semidwarf rice varieties. However, the rate of increase of rice production has slowed down, and the rate of population growth of rice consumers is now higher than the rate of increase of rice production. Severe food shortages are therefore likely to occur in 20–30 years if the trend is not reversed. To meet these food needs, rice varieties with higher yield potential are needed. The yield potential of the modern high-yielding varieties grown under the best tropical conditions is 10 t ha–1. A research program is under way to develop varieties with a yield potential of 15 t ha–1. One strategy aims to develop new rice plants with a harvest index of 0.6 (60% grain: 40% straw by weight) and with an increased ability for photosynthesis to increase total biological yield. The harvest index of the modern high-yielding varieties is 0.5. Such new varieties should have a yield potential of 12.5–13 tons ha–1. These new plant type varieties will be used to produce hybrid rices with a yield advantage of 25% over the best parent. Such hybrids would have a yield potential of 15 t ha–1.  相似文献   

14.
The basal area and productivity of managrove wetlands are described in relation to selected soil properties to understand the general pattern of optimum forest stature at the mouth of estuaries in the Everglades, such as the Shark River Slough, Florida (U.S.). The basal area of mangroves decreases from 40.4 m2 ha−1 and 39.7 m2 ha−1 at two stations 1.8 km and 4.1 km from the estuary mouth to 20.7 m2 ha−1 and 19.6 m2 ha−1 at two sites 9.9 km and 18.2 km from the mouth, respectively. The gradient in basal area at these four sites is mostly the result of approximately 34 yr of growth since Hurricane Donna. Wood productivity is higher in the lower estuary (10.7 Mg ha−1 yr−1 and 12.0 Mg ha−1 yr−1) than in the upper estuary (3.2 Mg ha−1 yr−1 and 4.2 Mg ha−1 yr−1). Porewater salinity among these four mangrove sites during seasonal sampling in 1994 and 1995 ranged from 1.6 g kg−1 to 33.5 g kg−1, while sulfide was generally<0.15 mM at all sites. These soil values indicate that abiotic stress cannot explain the decrease in forest structure along this estuarine gradient. Concentrations of nitrogen (N) and phosphorus (P) are more closely related to patterns of forest development, with higher soil fertility at the mouth of the estuary as indicated by higher concentrations of extractable ammonium, total soil P, and available P, along with higher ammonium production rates. The more fertile sites of the lower estuary are dominated by Laguncularia racemosa, whereas the less fertile sites in the intermediate and upper estuary are dominated by Rhizophora mangle. Relative N mineralization per unit of total N is higher in the lower estuary and is related positively to concentrations of available P, indicating the importance of turnover rates and nutrient interactions to soil fertility. Concentrations of Ca-bound P per volume soil in the lower estuary is 40-fold higher than in the upper estuary, and along with an increase in residual P in the upper estuary, indicate a shift from mineral to organic P along the estuarine gradient. Mineral inputs to the mouth of Shark River estuary from the Gulf of Mexico (rather than upland inputs) apparently control the patterns of mangrove structure and productivity.  相似文献   

15.
The chronology of near-surface sediments in Lake Illawarra has been investigated using radiocarbon dating and anthropogenically derived substances including trace metals, ash, and137Cs. Sediments at depths about 1 m below the water-sediment interface ranged in age from Modern to 786 calendar years bp on the basis of radiocarbon dating ofNotospisula trigonella valves. Multiple marker (for example ash-trace metals) depth-concentration sediment profiles yielded estimates of sedimentation rate ranging from 3 to 5 mm yr–1 at Griffins Bay to more than 16 mm yr–1 at Macquarie Rivulet. Sedimentation rates of approximately 10 mm yr–1 appeared to be typical of the western and southwestern portions of the lagoon. Rates of sediment accretion, prior to catchment clearing, urbanization, and industrialization have been estimated at less than 1 mm yr–1, thus indicating a general tenfold increase in sediment accumulation adjacent to the western foreshore caused by catchment development. Accelerated sedimentation in shallow coastal lagoons constitutes significant environmental impacts including shoaling, degradation of seagrass beds, and increased turbidity with consequent loss of aesthetic appeal. Management policy should be directed at attempts to reduce the amount of sediment input by the construction of strategically placed sediment retention ponds. Siltation within the shallow embayments of Lake Illawarra could be ameliorated by a carefully planned program of dredging.  相似文献   

16.
To analyze the development of pine ecosystems on lignite and pyrite containing mine soils, four pine stands with ages of 3–35 years were investigated in a chronosequence approach. Bulk precipitation, throughfall and soil solution in depths of 20, 40, 70 and 100 cm were studied over a three-year period to determine element fluxes in these forest ecosystems on extreme acidic and saline soils.Element budgets are controlled by the processes induced by pyrite oxidation such as intensive weathering of primary minerals, precipitation and leaching of secondary phases.Despite low water fluxes, element outputs can reach extraordinary high values due to very high concentrations in the soil solution. Although element outputs decrease drastically with stand age, respectively, site age, they exceed those of comparable pine stands on non-mine sites. Nitrogen release from the lignite fraction represents a special characteristic of the examined substrates. Nitrogen losses beneath the rooted zone can be 34 kg N ha−1 yr−1 in 100 cm depth. Element input and output in the examined ecosystems are far from balance. Closed cycling of nutrients seems to be recognizable in the case of potassium.  相似文献   

17.
Fluoride analyses display downward decreasing pore water gradients in Peru shelf phosphatic muds that require diffusion from the overlying seawater into the sediment column and removal by reaction within the upper few tens of centimeters, presumably by incorporation into carbonate fluorapatite. The profiles can be modeled as first-order F-removal with rate constants of ~3 yr?1 and asymptotic F-concentrations deep in the cores of 35–45 μM, almost one-half the seawater value. The integrated flux of fluoride from seawater into organic-rich shelf sediments in coastal-upwelling zones (phosphatic muds) yields a contemporaneous global F-burial of 0.54 × 1010 mol-F yr?1, about one-fifth the burial in other sinks (mostly carbonates and opal). The associated burial flux of phosphorus in shelf phosphorites is about 1.6 × 1010 mol-P yr?1, comparable to P-burial in the deep sea with organic matter (~1.4 × 1010 mol yr?1) and biogenic carbonates (~1.4 × 1010 mol yr?1). Thus phosphorite formation on the Peru shelf is a significant contemporaneous process.  相似文献   

18.
 The yearly nutrient supply from land and atmosphere to the study area in SW Kattegat is 10 900 tons of N and 365 tons of P. This is only few percent of the supply from adjacent marine areas, as the yearly transport through the study area is 218 000 tons of N and 18 250 tons of P. Yearly net deposition makes up 1340 tons of N (on average 2.5 g m–2 yr–1) and 477 ton of P (on average 0.9 g m–2 yr–1). Shallow-water parts of the study area have no net deposition because of frequent (>35% of the year) resuspension. Resuspension frequency in deep water is <1% of the year. Resuspension rates, as averages for the study area, are 10–17 times higher than net deposition rates. Because of resuspension, shallow-water sediments are coarse lag deposits with small amounts of organic matter (1.1%) and nutrients (0.04% N and 0.02% P). Deep-water sediments, in contrast, are fine grained with high levels of organic matter (11.7%) and nutrients (0.43% N and 0.15% P). Laboratory studies showed that resuspension changes the diffusive sediment water fluxes of nutrients, oxygen consumption, and penetration into the sediment. Fluxes of dissolved reactive phosphate from sediment to water after resuspension were negative in organic-rich sediments (13.2% organic matter) with low porosity (56) and close to zero in coarse sediments with a low organic matter content (2.3%) and high porosity (73). Fluxes of inorganic N after resuspension were reduced to 70% and 0–20% in relation to the rates before resuspension, respectively. Received: 10 July 1995 · Accepted: 19 January 1996  相似文献   

19.
Aquatic primary productivity, mangrove ecology, and fish community dynamics were investigated in the Teacapán-Agua Brava lagoon-estuarine system, the most extensive mangrove ecosystem on the Pacific coast of Mexico with three species of mangroves distributed heterogeneously (Laguncularia racemosa, Rhizophora mangle, andAvicennia germinans). Tree density was 3,203 trees ha?1 and basal area was 14.0 m2 ha?1. Litterfall was 1,417 g m?2 yr?1, characteristic of a productive riverine forest. The degradation constant forLaguncularia racemosa leaves varied from 1.71 to 4.7 yr?1 and mean annual net aquatic productivity was 0.41 g C m?3 d?1. There were high concentrations of humic substances (up to 150 mg l?1) early in the wet season. Seasonal variations of the above parameters seemed closely related to the ecology of fish populations. There were 75 fish species distributed in two principal assemblages associated with wet and dry seasons. Diversity and biomass analysis indicated 18 dominant species. Total biomass of the community in this coastal system was estimated at 10 g wet wt m?2. The highest biomass occurred in the wet season. The most common fish species wereMugil curema, Achirus mazatlanus, Galeichthys caerulescens, Arius liropus, Diapterus peruvianus, Lile stolifera, Centropomus robalito, andEucinostomus sp., all of which have fishery importance. Primary productivity and fish community ecology are controlled by habitat characteristics, river discharge, and climatic seasonality.  相似文献   

20.
We utilize regional GPS velocities from Luzon, Philippines, with focal mechanism data from the Harvard Centroid Moment Tensor (CMT) Catalog, to constrain tectonic deformation in the complex plate boundary zone between the Philippine Sea Plate and Eurasia (the Sundaland block). Processed satellite imagery and digital elevation models are used with existing gravity anomaly, seismicity, and geologic maps to define a suite of six elastic blocks. Geodetic and focal mechanism data are inverted simultaneously to estimate plate rotations and fault-locking parameters for each of the tectonic blocks and faults comprising Luzon. Major tectonic structures that were found to absorb the plate convergence include the Manila Trench (20–100 mm yr− 1) and East Luzon Trough ( 9–15 mm yr− 1)/Philippine Trench ( 29–34 mm yr− 1), which accommodate eastward and westward subduction beneath Luzon, respectively; the left-lateral strike-slip Philippine Fault ( 20–40 mm yr− 1), and its northward extensions, the Northern Cordillera Fault ( 17–37 mm yr− 1 transtension), and the Digdig Fault ( 17–27 mm yr− 1 transpression). The Macolod Corridor, a zone of active volcanism, crustal thinning, extension, and extensive normal and strike-slip faulting in southwestern Luzon, is associated with left-lateral, transtensional slip of  5–10 mm yr− 1. The Marikina Fault, which separates the Central Luzon block from the Southwestern Luzon block, reveals  10–12 mm yr− 1 of left-lateral transpression. Our analysis suggests that much of the Philippine Fault and associated splays are locked to partly coupled, while the Manila and Philippine trenches appear to be poorly coupled. Luzon is best characterized as a tectonically active plate boundary zone, comprising six mobile elastic tectonic blocks between two active subduction zones. The Philippine Fault and associated intra-arc faults accommodate much of the trench-parallel component of relative plate motion.  相似文献   

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