Renewed uplift at the Yellowstone Caldera measured by leveling surveys and satellite radar interferometry

 A first-order leveling survey across the northeast part of the Yellowstone caldera in September 1998 showed that the central caldera floor near Le Hardy Rapids rose 24±5 mm relative to the caldera rim at Lake Butte since the previous survey in September 1995. Annual surveys along the same traverse from 1985 to 1995 tracked progressive subsidence near Le Hardy Rapids at an average rate of –19±1 mm/year. Earlier, less frequent surveys measured net uplift in the same area during 1923–1976 (14±1 mm/year) and 1976–1984 (22±1 mm/year). The resumption of uplift following a decade of subsidence was first detected by satellite synthetic aperture radar interferometry, which revealed approximately 15 mm of uplift in the vicinity of Le Hardy Rapids from July 1995 to June 1997. Radar interferograms show that the center of subsidence shifted from the Sour Creek resurgent dome in the northeast part of the caldera during August 1992 to June 1993 to the Mallard Lake resurgent dome in the southwest part during June 1993 to August 1995. Uplift began at the Sour Creek dome during August 1995 to September 1996 and spread to the Mallard Lake dome by June 1997. The rapidity of these changes and the spatial pattern of surface deformation suggest that ground movements are caused at least in part by accumulation and migration of fluids in two sill-like bodies at 5–10 km depth, near the interface between Yellowstone's magmatic and deep hydrothermal systems. Received: 30 November 1998 / Accepted: 16 April 1999     

Estrogen in a karstic aquifer

Adverse impacts on the health of some fish populations, such as skewed sex distributions, have been noted in surface waters and in laboratory experiments with relatively low concentrations (above 25 ng/L) of natural estrogen (17 beta-estradiol--E2). Sources of E2 to surface and ground waters can include avian, human, and mammalian waste products. The Ozark Plateau Aquifer (OPA) is a karstic basin that receives a significant portion of its water through losing reaches of rivers. Thus, there is a direct connection between surface water and ground water. The OPA was targeted for an E2 study to assess the potential for adverse health effects to aquatic organisms living in the system. Eight springs, which drain the aquifer, were sampled quarterly. The concentrations of E2 in the OPA ranged from 13 to 80 ng/L. For any one sampling event, the concentrations of E2 at the spring waters were statistically similar; however, the concentrations of E2 at all springs varied throughout the year. At Maramec Spring, one of the larger springs, the E2 concentration, was correlated with discharge. Based on the correlation between discharge and E2 concentration, aquatic organisms living in the plateau or in its discharged waters, including the threatened southern cavefish T. subterraneus, are exposed to concentration of E2 above 25 ng/L approximately 60% of the time. This implies that organisms living in karst basins throughout the OPA are likely exposed to E2 concentrations that may adversely impact their reproductive success for a significant portion of each year.     

干涉合成孔径雷达及其在火山研究中的应用(第二部分:阿拉斯加火山的InSAR成像)(英文)

干涉合成孔径雷达是一项能够对地表变形进行测量的遥感技术,在一个巨大区域内,它的变形测量精度可达亚厘米级,而其空间分辨率则在数十米以内。本文对我们应用InSAR技术对阿拉斯加火山进行研究的最新成果进行了总结,同时包括火山的喷发和非喷发活动。这些研究成果表明InSAR不仅能够增进我们对阿拉斯加火山活动的理解,而且还能够增强我们对未来火山喷发情况及其灾害的预测能力。     

Enhancement of long period components of recorded and synthetic ground motions using InSAR

Tall buildings and flexible structures require a better characterization of long period ground motion spectra than the one provided by current seismic building codes. Motivated by that, a methodology is proposed and tested to improve recorded and synthetic ground motions which are consistent with the observed co-seismic displacement field obtained from interferometric synthetic aperture radar (InSAR) analysis of image data for the Tocopilla 2007 earthquake (M_w=7.7) in Northern Chile. A methodology is proposed to correct the observed motions such that, after double integration, they are coherent with the local value of the residual displacement. Synthetic records are generated by using a stochastic finite-fault model coupled with a long period pulse to capture the long period fling effect.It is observed that the proposed co-seismic correction yields records with more accurate long-period spectral components as compared with regular correction schemes such as acausal filtering. These signals provide an estimate for the velocity and displacement spectra, which are essential for tall-building design. Furthermore, hints are provided as to the shape of long-period spectra for seismic zones prone to large co-seismic displacements such as the Nazca-South American zone.     

DigitalOcean: building a platform for scientific collaboration and social and media sharing on the Drupal content management system

The DigitalOcean (DO) Project is designed to bring essential Web 2.0 capabilities to an open-source software platform built for scientific collaboration and publishing. The DO platform is being built using the Drupal content management system (CMS). The following are some of the core features of the proposed platform: social networking, media/data sharing/publishing, and collaboration spaces for scientific virtual organizations (VO); active support for VO governance and reputation systems for members and objects; Creative Commons licensing, support for preprint archives and micro-articles, and; professional user-profiles that can be saved as well formatted biosketches. The DO platform serves as a collaboration environment for active research teams, a personal repository for individual researchers, an aggregation/filter for science information, and a scientific publishing tool. This article will outline the history and goals of the DO Project, the core technology concerns and solutions, and the opportunities that this new platform will bring to scientists across the planet.     

An Empirical Method for the Spatial Interpolation of Monthly Precipitation within California

An empirical method for interpolating monthly precipitation totals within California is described and evaluated. Using 120 monthly precipitation totals observed from 1961-1970 at each of 90 randomly selected stations in California and a P-mode principal components analysis of a co-variance matrix, four independent sources of precipitation variability were identified and quantitatively paraphrased. The four principal components were then linked to three representative stations by polynomial regression. From these relationships, monthly precipitation totals can be interpolated anywhere in the state by reversing the principal components computations. The required input includes: a monthly precipitation total, for the month of interest, from each of the three representative stations as well as isarithmically interpolated estimates of the component loadings and station means which were derived from the initial (1961-1970) data set. A major asset of the procedure is that it only requires three pieces of new information (i.e., the monthly totals from the representative stations) in order to interpolate monthly precipitation anywhere in California for any month of interest. Interpolations were quantitatively compared to measured values at 51 randomly selected stations over the period 1971-1975 and they were, in most cases, above 80% effective in reproducing the observed, 5-year records.     

The Variation of Solar Wind Correlation Lengths Over Three Solar Cycles

We present the results of a study of solar wind velocity and magnetic field correlation lengths over the last 35 years. The correlation length of the magnetic field magnitude λ _|B| increases on average by a factor of two at solar maxima compared to solar minima. The correlation lengths of the components of the magnetic field l_BXYZ\lambda_{B_{XYZ}} and of the velocity l_VYZ\lambda_{V_{YZ}} do not show this change and have similar values, indicating a continual turbulent correlation length of around 1.4×10⁶ km. We conclude that a linear relation between λ _|B|, VB ², and Kp suggests that the former is related to the total magnetic energy in the solar wind and an estimate of the average size of geoeffective structures, which is, in turn, proportional to VB ². By looking at the distribution of daily correlation lengths we show that the solar minimum values of λ _|B| correspond to the turbulent outer scale. A tail of larger λ _|B| values is present at solar maximum causing the increase in mean value.     

Fluid and Solute Transport from a Conduit to the Matrix in a Carbonate Aquifer System

Within carbonate systems, the working hypothesis suggests that when a conduit is flooded fluid and solute migrate from the conduit into the matrix. This flux of fluid and solute into the matrix creates a reservoir that can be slowly released once the flooding recedes. Although hypothesized, these fluxes have never been measured. To quantify the distance that a fluid and solute would move into a matrix, the fluxes of fluid and solute from a conduit into a matrix were simulated for nine different carbonate aquifer systems. Two independent numerical approaches were used to simulate (1) fluid flux into the matrix and (2) solute flux into the matrix during a flooding event. When flooding occurs within the conduit, the volume of water transported into and stored in the matrix with a high porosity and high hydraulic conductivity (Floridan Aquifer) was less than 0.34 m³ along a 1 m length of conduit, resulting in a penetration depth of 7.2×10⁻² m into the matrix. In a low porosity and low hydraulic conductivity matrix (Ozark Plateau), the volume of water transported into and stored in the matrix was less than 6.85×10⁻⁵ m³ along a 1 m length of conduit, resulting in a penetration depth of 2.0×10⁻⁴ m into the matrix. Simulated solute flow shows that less than 0.1% of the solute moves in to the matrix. The two approaches demonstrate that during high flow conditions fluid and solute are forced through the conduits, with very little moving into the carbonate matrix. Once the fluid and solute enter a conduit and are moving, they will remain in the conduit until they are discharged at an outlet. Thus, a carbonate matrix does not become a reservoir for solute and fluid during a high-flow event.