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111.
Jordan Van Aalsburg John B. Rundle Lisa B. Grant Paul B. Rundle Gleb Yakovlev Donald L. Turcotte Andrea Donnellan Kristy F. Tiampo Jose Fernandez 《Pure and Applied Geophysics》2010,167(8-9):967-977
In weather forecasting, current and past observational data are routinely assimilated into numerical simulations to produce ensemble forecasts of future events in a process termed “model steering”. Here we describe a similar approach that is motivated by analyses of previous forecasts of the Working Group on California Earthquake Probabilities (WGCEP). Our approach is adapted to the problem of earthquake forecasting using topologically realistic numerical simulations for the strike-slip fault system in California. By systematically comparing simulation data to observed paleoseismic data, a series of spatial probability density functions (PDFs) can be computed that describe the probable locations of future large earthquakes. We develop this approach and show examples of PDFs associated with magnitude M > 6.5 and M > 7.0 earthquakes in California. 相似文献
112.
Francesca Cigna Hannah Jordan Luke Bateson Harry McCormack Claire Roberts 《Pure and Applied Geophysics》2015,172(11):2965-2995
113.
To estimate the average density contrast associated with the continental tectosphere, we separately project the degree 2–36 non-hydrostatic geoid and free-air gravity anomalies onto several tectonic regionalizations. Because both the regionalizations and the geoid have distinctly red spectra, we do not use conventional statistical analysis, which is based on the assumption of white spectra. Rather, we utilize a Monte Carlo approach that incorporates the spectral properties of these fields. These simulations reveal that the undulations of Earth's geoid correlate with surface tectonics no better than they would were it randomly oriented with respect to the surface. However, our simulations indicate that free-air gravity anomalies correlate with surface tectonics better than almost 98% of our trials in which the free-air gravity anomalies were randomly oriented with respect to Earth's surface. The average geoid anomaly and free-air gravity anomaly over platforms and shields are significant at slightly better than the one-standard-deviation level: −11±8 m and −4±3 mgal, respectively. After removing from the geoid estimated contributions associated with (1) a simple model of the continental crust and oceanic lithosphere, (2) the lower mantle, (3) subducted slabs, and (4) remnant glacial isostatic disequilibrium, we estimate a platform and shield signal of −8±4 m. We conclude that there is little contribution of platforms and shields to the gravity field, consistent with their keels having small density contrasts. Using this estimate of the platform and shield signal, and previous estimates of upper-mantle shear-wave travel-time perturbations, we find that the average value of ∂lnρ/∂lnνs within the 140–440 km depth range is 0.04±0.02. A continental tectosphere with an isopycnic (equal-density) structure (∂lnρ/∂lnνs=0) enforced by compositional variations is consistent with this result at the 2.0σ level. Without compositional buoyancy, the continental tectosphere would have an average ∂lnρ/∂lnνs≈0.25, exceeding our estimate by 10σ. 相似文献
114.
Previous studies using observations made at low spatial and spectral resolution showed that the resonance lines of He i and He ii are anomalously strong in the quiet Sun when compared with other transition region lines formed at similar temperatures. Here, the higher spatial and spectral resolution provided by the Coronal Diagnostic Spectrometer ( cds ) instrument on board the Solar and Heliospheric Observatory ( SOHO ) is used to re-examine the behaviour of the He i and He ii lines and other transition region lines, in quiet regions near Sun centre. Supergranulation cell boundaries and cell interiors are examined separately. Near-simultaneous observations with the sumer instrument provide information on the lower transition region and the electron pressure. While the lines of He i and He ii have a common behaviour, as do the other transition region lines, the behaviour of the helium lines relative to the other transition region lines is significantly different. The emission measure distributions that account for all transition region lines, except those of helium, fail to produce sufficient emission in the He i and He ii resonance lines by around an order of magnitude, in both supergranulation cell boundary and cell interior regions. The electron pressure appears to be higher in the cell interiors than in the average cell boundaries, although the uncertainties are large. While the VAL-D model gives a closer match to the He i 584.3-Å line, it does not successfully reproduce other transition region lines. 相似文献
115.
Geological and archaeological investigations on the western Alaska Peninsula establish relationships between postglacial sea level changes and regional settlement patterns, which are linked to the spatial and temporal distribution of marine and estuarine resources. Isostatic emergence dominated relative sea‐level changes since deglaciation, but erosional landforms and gaps in the archaeological record suggest that site preservation has varied because of the interplay of eustatic sea level rise, isostatic uplift, and tectonic deformation. Coastal subsidence associated with a major earthquake about 2200 yr B.P. is linked with a 300‐year hiatus in the regional archaeological record. A shift from estuarine to littoral and offshore resources following this period demonstrates the impact of such dynamic sea level fluctuations on the shape and biological productivity of the coastal zone. However, changes in village organization, house form, and subsistence base that define several archaeological phases arise from both environmental and sociopolitical instability. Models of culture change should accommodate local and regional geological boundary conditions in the North Pacific and similarly dynamic settings. © 2000 John Wiley & Sons, Inc. 相似文献
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In 2003, chlorofluorocarbon (CFC) apparent ages, major ion chemistry and C isotopes were determined in nine springs from Sagehen Basin, a high elevation watershed in the eastern Sierra Nevada. Springs with similar apparent ages, which ranged between 15 and 45 a, had very similar chemistry despite being found in different areas of the watershed. In agreement with earlier studies, concentrations of rock-derived cations (Ca2+ and Na+), conductivity, temperature and pH increase with apparent age, documenting the chemical evolution of this groundwater system. In contrast with the cation data, δ13C and ΣCO2 show no correlation with apparent age. δ13C displays a strong linear relationship with 1/ΣCO2 (R2 = 0.91). This is consistent with results from a previously developed soil respiration/diffusion model. Spring radiocarbon content ranged between 85 and 110 pmc and varied with apparent age, whereby the youngest groundwater has the highest radiocarbon values. The spring radiocarbon is set by the soil pCO2 and its trend can be best described assuming the soil CO2 is composed of a mixture of 50–66% fast- (15–25 a) and 33–50% slow- (4 ka) cycling components. These results are consistent with previous soil C studies. The C isotope data indicate that in Sagehen Basin the groundwater ΣCO2 is inherited from the soil zone with little, if any, contribution from the dissolution of disseminated calcite. 相似文献
120.
Snowmelt‐fed springs and small (0.5 km2) upland catchments in alpine areas of the western United States contribute significantly to the quantity and inorganic chemistry of water delivered to downstream basins but have not been studied extensively. Mineral weathering, transit time, and hydrologic mixing control the solute chemistry of waters that drain the upland zone of Niwot Ridge, Colorado Front Range, and adjacent areas in the granitic core of the Southern Rocky Mountains. Water in 37 springs sampled in this study flows in generally short steep paths (~0.3 km) through shallow regolith with mean transit times (MTT) of weeks to months, producing solutions dominated by Si, Ca2+, Na+, and HCO3?, locally SO42?. Rock type is a significant control on spring, surface, and shallow groundwater chemistry, and plagioclase (oligoclase) is the major source of dissolved Na+ and Si. Concentrations of Ca2+ exceed stoichiometric predictions of oligoclase weathering by ~3.5×; excess Ca2+ likely represents weathering of aeolian material, vein calcite, or trace minerals. Concentrations of base cations and Si increase slowly with estimated MTT of 0.2 years for Niwot Ridge spring waters, and several years for shallow groundwater sampled by wells. Chemical weathering of silicate minerals is slow with estimated rates of ~2.0 and 0.2 pmol·m?2·s?1 for oligoclase and microcline, respectively; the most mineralized spring waters are saturated only with respect to kaolinite and montmorillonite. More than 50% of the dissolved base cations + Si measured in Boulder Creek at Orodell (~25 km downstream) accumulate before water emerges from alpine springs on Niwot Ridge. Warming global temperatures are shifting more high‐elevation precipitation to rain, potentially changing run‐off patterns, transit time, and solute loads. Acquisition of solutes by alpine waters thus has implications far beyond small upland catchments. 相似文献