Estimating explosion yield by analytical waveform comparison

Summary. The yields of 28 underground nuclear explosions at NTS (25 on Pahute Mesa) are estimated by applying a relative waveform analysis called intercorrelation to 1256 teleseismic short-period P -waves recorded at 74 WWSSN and CSN stations. Corrections for the effects of pP interference and yield-scaling of the explosion source functions are determined and applied to the waveforms, enabling analytical comparison of signals from events with different yields and burial depths. The procedure accounts for common receiver and propagation effects. Relative explosion source strengths in the 0.5–2.0 Hz frequency band are determined, with results of near-field modelling of strong ground motions establishing the absolute source spectral levels. Four events with detailed near-field models are used as master events in the intercorrelation process, and it is demonstrated that the relative source strengths are better resolved than the absolute values. Events with announced yields are used to determine empirical relations between yield and source strength, which in turn predict the yields of the other events. These yield estimates are shown to be comparable with those obtained by standard m _b and relative amplitude analysis. The analytical waveform comparisons also provide estimates of the pP parameters for each event, and criteria for identifying anomalous events, such as PIPKIN and MUENSTER, for which the waveforms differ from those of other events in the test site. Possible mechanisms affecting the anomalous events are considered. Pahute Mesa is shown to be a distinct subsite within NTS, with different teleseismic amplitude and waveform variations than observed at other subsites.     

The PWaves From the Amchitka Island Explosions

Summary. There is evidence that the equivalent seismic sources of the Amchitka Island explosions — Longshot, Milrow and Cannikin — depart significantly from the simple model of a point compressional-source in a layered elastic-medium. Consequently modelling the observed seismograms using standard source-models may not be the most efficient method of determining source properties. Here an alternative to modelling is used to obtain information on the seismic sources due to the explosions. Broad-band (BB) estimates of the P signals are obtained from the short-period (SP) seismograms, corrected for attenuation, and interpreted in terms of P, pP and radiation from secondary sources. the main conclusions are:
(i) BB estimates of the radiated displacement from the explosions can be obtained with only a small reduction in the signal-to-noise ratio seen on SP seismograms;
(ii) observations of differences in pulse amplitudes and spectra are not necessarily due to differences in anelastic attenuation;
(iii) P and pP at a given station may differ in shape so that notches in the signal spectrum may not be related to source depth;
(iv) there is evidence of arrivals that others have identified as due to slap-down but which could be interpreted as an overshoot to pP;
(v) direct interpretation of the estimated ground displacement is a better procedure for determining the seismic source properties of explosions than modelling SP seismograms using idealised models as a starting point.     

The accuracy of models derived by WKBJ waveform inversion

Summary . In this paper the accuracy of velocity-depth profiles derived by matching WKBJ seismograms to observations is quantitatively evaluated. Seismograms computed with the WKBJ method are generally quite reliable but possess predictable, systematic inaccuracies in the presence of strong velocity gradients. The effects of these inaccuracies on models derived through WKBJ waveform inversion are studied, using reflectivity seismograms as 'data'. The velocity structure used is an oceanic lithosphere model that contains several transition regions separated by relatively homogeneous layers, producing partially-reflected reverberations in the reflectivity synthetics that are absent from the WKBJ seismograms. The inversion incorporates the 'jumping' strategy to solve for the smoothest models consistent with the data. We find these solutions to be independent of the starting model and to have a stable basic structure that agrees well with the correct model. The differences, everywhere less than a seismic wavelength, depend on the frequency content of the seismograms. Reverberations in the reflectivity seismograms that are well separated from WKBJ arrivals are treated as 'noise' in the inversion.     

Regional 3-D heterogeneities by waveform inversion – application to the Atlantic area

The waveform inversion method described in Woodhouse & Dziewonski (1984) was modified to retrieve regional scale 3-D heterogeneities by using the minor arc part of seismograms. The lateral heterogeneities are expanded horizontally into blocks (10°× 10°) and radially into Legendre polynomials up to order 3 (0–670 km), and thus the results show much fine details of lateral variation than previous global scale studies. We assumed that the heterogeneities produce the perturbation of eigenfrequencies which are the minor arc average of local eigenfrequency shift. We applied the method to the upper mantle beneath the Atlantic Ocean and its environments. Care was taken about the weighting of the data set. We found that the fit of each seismogram became better when the weighting of each seismogram is proportional to the inverse of initial data residuals. Resolution is good in the triangular region surrounded by South America, Europe, and North America. Resolution is not good in the South Atlantic because of the poor path coverage. Depth resolution is not clear, because of the use of Legendre polynomials, though the results suggest a broad half-width of the order of 200 km or more. We found some similarities between previous global studies and our results. For example, low velocities beneath the East Pacific Rise, Chile Rise and Azores triple junction and a high velocity Canadian shield are obtained. However, there are also differences; the high-velocity zone beneath the Brazilian shield at shallow depth is not a prominent feature in this study. Instead, we found a somewhat unexpected feature near the Romanche and Vema fracture zones where shallow positive anomalies exist. Smoothed results calculated by the spherical harmonic expansion are also shown for the purpose of comparison with global studies.     

非农占用耕地损失估算

经济发展过程中把耕地转变为非农业用地，是我国耕地减少的一个重要原因，耕地的过度减少会对经济的发展造成一定的影响，为了了解非农占用耕地对经济发展造成的负面影响，文章首先对非农占用耕地的损失构成进行了分析，并把它划分为4个部分，然后提出用投入产出的分析方法来对当期间损失部分进行估算。     

Alluvial storage and the long-term stability of sediment yields

Several recent studies have shown general consistency of fluvial denudation rates over long time periods, or historical and contemporary sediment yields of the same general magnitude as sediment yields or accumulation rates over geologic time. This consistency of fluvial sediment export from some drainage basins, despite substantial climate, hydrological, ecological, base level, and other environmental changes, suggests that long‐term sediment yields may be controlled by factors that are independent of and overwhelm environmental changes (e.g. tectonics), or that the fluvial sediment system is at some level dynamically stable. The latter is explored via a model based on the notion that all debris produced by weathering within a drainage basin over any time period is either retained as part of the regolith, transported out of the basin as solid or dissolved sediment yield, or stored as alluvium within the fluvial system. This system is dynamically stable if alluvium is always potentially available for transport; e.g. to be converted to yield, and if regolith development exerts a negative feedback on weathering rates. This supports the argument that the long‐term consistency of sediment yields (where it exists) may be attributable to the storage and remobilization of alluvium, which buffers the system against environmental change. Environmental changes are manifested primarily in reorganizations within the fluvial sediment system, such as variations between net increases and decreases in alluvial storage, and changes in the spatial locus of deposition. These ideas are illustrated and tested using data from the lower Trinity River in southeast Texas.     

Estimating rainfall erosivity by incorporating seasonal variations in parameters into the Richardson model

Rainfall erosivity is an important climatic factor for predicting soil loss. Through the application of high-resolution pluviograph data at 5 stations in Huangshan City, Anhui Province, China, we analyzed the performance of a modified Richardson model that incorporated the seasonal variations in parameters α and β. The results showed that (1) moderate to high seasonality was presented in the distribution of erosive rainfall, and the seasonality of rainfall erosivity was even stronger; (2) seasonal variations were demonstrated in both parameters α and β of the Richardson model; and (3) incorporating and coordinating the seasonality of parameters α and β greatly improved the predictions at the monthly scale. This newly modified model is therefore highly recommended when monthly rainfall erosivity is required, such as, in planning soil and water conservation practices and calculating the cover-management factor in the Universal Soil Loss Equation (USLE) and Revised Universal Soil Loss Equation (RUSLE).     

Whole mantle SH velocity model constrained by waveform inversion based on three-dimensional Born kernels

A whole mantle SH velocity model is obtained by using a unique data set and techniques. Body and surface waveforms including major and multi-orbit phases are used as a data set and are inverted by using 3-D Born kernels. The resultant model, SH18CE, reveals the different natures of the two major upwelling systems: the strong low velocity anomalies beneath Africa extend for more than 1000 km from the core–mantle boundary (CMB), whereas those beneath the Pacific are restricted to 300–400 km from the CMB. The results also show the variable natures of stagnant slabs on the 670 discontinuity around Japan: the depths of the strongest high velocity anomalies within the stagnant slabs are different region by region, which is consistent with the detailed delay time tomography model in this area.