Imaging the Seismic Crustal Structure of the Western Mexican Margin between 19°N and 21°N     

Rafael Bartolomé  Juanjo Dañobeitia  François Michaud  Diego Córdoba  Luis A. Delgado-Argote 《Pure and Applied Geophysics》2011,168(8-9):1373-1389

Three thousand kilometres of multichannel (MCS) and wide-angle seismic profiles, gravity and magnetic, multibeam bathymetry and backscatter data were recorded in the offshore area of the west coast of Mexico and the Gulf of California during the spring 1996 (CORTES survey). The seismic images obtained off Puerto Vallarta, Mexico, in the Jalisco subduction zone extend from the oceanic domain up to the continental shelf, and significantly improve the knowledge of the internal crustal structure of the subduction zone between the Rivera and North American (NA) Plates. Analyzing the crustal images, we differentiate: (1) An oceanic domain with an important variation in sediment thickness ranging from 2.5 to 1 km southwards; (2) an accretionary prism comprised of highly deformed sediments, extending for a maximum width of 15 km; (3) a deformed forearc basin domain which is 25 km wide in the northern section, and is not seen towards the south where the continental slope connects directly with the accretionary prism and trench, thus suggesting a different deformational process; and (4) a continental domain consisting of a continental slope and a mid slope terrace, with a bottom simulating reflector (BSR) identified in the first second of the MCS profiles. The existence of a developed accretionary prism suggests a subduction–accretion type tectonic regime. Detailed analysis of the seismic reflection data in the oceanic domain reveals high amplitude reflections at around 6 s [two way travel time (twtt)] that clearly define the subduction plane. At 2 s (twtt) depth we identify a strong reflection which we interpret as the Moho discontinuity. We have measured a mean dip angle of 7° ± 1° at the subduction zone where the Rivera Plate begins to subduct, with the dip angle gently increasing towards the south. The oceanic crust has a mean crustal thickness of 6.0–6.5 km. We also find evidence indicating that the Rivera Plate possibly subducts at very low angles beneath the Tres Marias Islands.  相似文献   

Plio-pleistocene paleomagnetic record from the Michoacán-Guanajuato Monogenetic Volcanic Field (Western Mexico)     

Rafael Maciel Peña  Avto Goguitchaichvili  Bernard Henry  Leda Sánchez-Bettucci  Juan Morales  Bertha Aguilar Reyes  Ana María Soler-Arechalde  Manuel Calvo-Rathert 《Studia Geophysica et Geodaetica》2011,55(2):311-328

The paleosecular variation (PSV) and polarity transitions are two major features of the Earth’s magnetic field. Both PSV and reversal studies are limited when age of studied units is poorly constrained. This is a case of Central and western Mexico volcanics. Although many studies have been devoted to these crucial problems and more than 200 paleomagnetic directions are available for the last 5 Ma, only few sites were dated directly. This paper presents new paleomagnetic results from seventeen independent cooling units in the Michoacán-Guanajuato Volcanic Field (MGVF) in western Mexico. Twelve sites are directly dated by ⁴⁰Ar/³⁹Ar or K-Ar methods and span from 2.78 to 0.56 Ma. The characteristic paleodirections are successfully isolated for 15 lava flows. The mean paleodirection (inclination I and declination D) obtained in this study is I = 28.8°, D = 354.9°, and Fisherian statistical parameters are k = 28, α₉₅ = 7.3°, N=15, which corresponds to the mean paleomagnetic pole position P_lat = 83.9°, P_long = 321.6°, K = 34, A₉₅ = 6.6°. The paleodirections obtained in present study compiled with those, previously reported from the MGVF, are practically undistinguishable from the expected Plio-Quaternary paleodirections. The paleosecular variation is estimated through the study of the scatter of the virtual geomagnetic poles giving S_F = 15.9 with S_U =21.0 and S_L = 12.7 (upper and lower limits respectively). These values agree reasonably well with the recent statistical Models. The oldest sites analyzed (the Santa Teresa and Cerro Alto) yield normal polarity magnetizations as expected for the cooling units belonging to the Gauss geomagnetic Chron. The interesting feature of the record comes from lava flows dated at about 2.35 Ma with clearly defined normal directions. This may point out the possible existence of a normal polarity magnetization in the Matuyama reversed Chron older than the Reunion and may be correlated to Halawa event interpreted as the Cryptochron C2r.2r-1. Another important feature of the geomagnetic record obtained from the MGVF is the evidence of fully reversed geomagnetic field within Bruhnes Chron, at about 0.56 Ma corresponding to the relative paleointensity minimum of global extent found in marine sediments at about 590 ka.  相似文献   

五里营氦气受水位影响分析   总被引：2，自引：1，他引：1  

王志惠  武晓东  朱石军  穆会泳  孔来顺  周尚伟 《地震地磁观测与研究》2011,32(5):90-93

延庆地震台五里营井逸出氦气受该井动水位异常变化影响,每日数据扰动大,影响原来的日变形态.对仪器的集气装置进行改造,把地面集气改为水下集气.既解决氦气受水位异常变化的影响问题,减小观测环境变化对氦气观测的影响,提高观测质量,对今后可能记录的地震前兆信息提供保障,对其他有此测项的台站有一定借鉴意义.  相似文献   

Hydraulic conductivity characterization of a karst recharge area using water injection tests and electrical resistivity logging     

Bárbara Angulo  Tomás Morales  Jesús A. Uriarte  Iñaki Antigüedad 《Engineering Geology》2011,117(1-2):90-96

Water injection tests and electrical logging are particularly useful techniques in the characterization of geological media in engineering works. In this paper these techniques in conjunction with cracks measurements obtained from drilling cores, were used in the characterization of a singular location in a karst massif. The aim of our work is to determine the hydraulic characteristics of the investigated site, as well as to establish the relationship between the data obtained by the different techniques used. Thus, electrical resistivity records and fracture data were obtained from two boreholes of 100 and 120 m depth. Hydraulic conductivity was calculated from 25 low-pressure water injection tests (LPT) carried out at different depths in both boreholes. The relationship between hydraulic conductivity and fracture frequency was not very statististically significant (R²: 0.062–0.672; σ_est: 0.61–1.575). Conversely, electrical resistivity and hydraulic conductivity had a great relationship (R²: 0.725–0.935; σ_est: 0.159–0.738), so the electrical resistivity may be related to the functionality of the fractures. Finally, the LPT is shown as a very practical tool for determining the degree of the hydraulically interconnection with the surroundings, for establishing the hydraulic conductivity profile and for obtaining a measure of soil erosionability according to the significance of the fracture washing out processes recorded.  相似文献   

气象因子对哈密市大气可吸入颗粒物浓度的影响分析   总被引：2，自引：0，他引：2  

慕彩芸  屠月青  冯瑶 《气象与环境科学》2011,34(Z1):75-79

采用2007-2008年哈密市气象及环境数据,分析可吸入颗粒物(PM10)对哈密市空气质量的影响以及风速风向、沙尘天气、降水、气温、气压、相对湿度与PM10浓度的相互关系.结果表明:哈密市的首要污染物为可吸入颗粒物.偏西风能够明显增大PM1o浓度.当平均风速＜2.0 m/s时,随着风速的增大PM10浓度逐渐减小;平均风...  相似文献   

Do long lived seabirds reduce the negative effects of acute pollution on adult survival by skipping breeding? A study with European storm petrels (Hydrobates pelagicus) during the "Prestige" oil-spill     

Zabala J  Zuberogoitia I  Martínez-Climent JA  Etxezarreta J 《Marine pollution bulletin》2011,62(1):109-115

We estimated the survival probability of breeding European storm petrels before, during and after a severe oil-spill. We hypothesized that petrels might have deserted the breeding colony to maximize their own survival probability and we expected no major change on adult survival probabilities as a consequence of the spill. We used an information-theoretical approach and multi-model inference to assess the strength of the evidence in favour of different hypotheses.Evidence contained in the data clearly supported the non-effect of the spill on adult survival hypothesis while punctual impact of the spill on survival and expanded (3 years) impact alternatives received less support. The effect size of the spill on averaged survival estimates was negligible in every case. We suggest that petrels minimized the impact of acute pollution by not investing in reproduction. We suggest that short-medium term management actions after oil-spills and similar catastrophes should focus on ecosystem restoration.  相似文献   

Metal concentrations in water and sediments from tourist beaches of Acapulco, Mexico     

Jonathan MP  Roy PD  Thangadurai N  Srinivasalu S  Rodríguez-Espinosa PF  Sarkar SK  Lakshumanan C  Navarrete-López M  Muñoz-Sevilla NP 《Marine pollution bulletin》2011,62(4):845-850

A survey on the metal concentrations (As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr, V, Zn) in beach water and sediments is reported from the tourist destination of Acapulco city on the Pacific coast of Mexico. The concentration of dissolved trace metals (DTMs) in beach water and acid leachable trace metals (ALTMs) in sediments indicated that they are anthropogenic in nature due to the increased tourist activities in the crowded beach locations. The statistical analysis indicates Fe and Mn play a major role as metal scavengers in both the medium (water and sediment) and the higher value of other metals is site specific in the study area, indicating that they are transported from the local area. Comparison results suggest that the beach water quality has deteriorated more than the sediments and special care needs to be taken to restore the beach quality.  相似文献   

利用IRS-P5影像制作1∶50000 3D产品的试验研究     

郑福海  杨木  宋红艳  王铁军 《测绘与空间地理信息》2011,(6):117-120

讨论了利用IRS-P5卫星遥感影像立体模型进行1∶50000 DEM,DOM,DLG等地理信息产品生产的相关问题,并进行了精度检测;同时与传统的航空摄影测量方法在原始资料获取、生产效率、工作量、数据成本等方面进行了对比分析。  相似文献   

Baseline heavy metals and metalloid values in blood of loggerhead turtles (Caretta caretta) from Baja California Sur, Mexico     

Ley-Quiñónez C  Zavala-Norzagaray AA  Espinosa-Carreón TL  Peckham H  Marquez-Herrera C  Campos-Villegas L  Aguirre AA 《Marine pollution bulletin》2011,62(9):1979-1983

Environmental pollution due to heavy metals is having an increased impact on marine wildlife accentuated by anthropogenic changes in the planet including overfishing, agricultural runoff and marine emerging infectious diseases. Sea turtles are considered sentinels of ecological health in marine ecosystems. The objective of this study was to determine baseline concentrations of zinc, cadmium, copper, nickel, selenium, manganese, mercury and lead in blood of 22 clinically healthy, loggerhead turtles (Caretta caretta), captured for several reasons in Puerto López Mateos, Baja California Sur, Mexico. Zinc was the most prevalent metal in blood (41.89 μg g⁻¹), followed by Selenium (10.92 μg g⁻¹). The mean concentration of toxic metal Cadmium was 6.12 μg g⁻¹ and 1.01 μg g⁻¹ respectively. Mean concentrations of metals followed this pattern: Zn > Se > Ni > Cu > Mn > Cd > Pb and Hg. We can conclude that blood is an excellent tissue to measure in relatively non-invasive way baseline values of heavy metals in Caretta caretta.  相似文献   

Influence of sieving time on the efficiency and accuracy of grain‐size analysis of beach and dune sands     

Jorge Román‐Sierra  Juan j. Muñoz‐perez  Marina Navarro‐Pons 《Sedimentology》2013,60(6):1484-1497

Grain size is a fundamental property of sediments and is commonly used to describe sedimentary facies and classify sedimentary environments. Among the various conventional techniques utilized to determine grain‐size frequency distributions, sieving is the most widely applied procedure. The accuracy of such analyses is, among other factors, strongly dependent on the sieving time. However, despite a substantial amount of research in this field, optimal sieving times for different types of sediments have, to date, not been established. In this article, the influence of sieving time on grain‐size analyses of medium‐grained microtidal and mesotidal beach and dune sands has been determined. To assess the precision of important textural parameters, such as median grain size, sorting, skewness and kurtosis, an error analysis was carried out for different sieving times (2, 5, 10, 15 and 20 minutes). After calibrating the analytical and sampling methodologies, significant deviations were registered when sieving time was less than 10 minutes. However, such deviations were very small and grain‐size distributions remained almost identical for sieving times of 10 minutes and longer, relative errors being as low as 0% in some cases.  相似文献