Postseismic Deformation Following the 1994 Northridge Earthquake Identified Using the Localized Hartley Transform Filter

Here we present a new mathematical tool, the localized Hartley (HL) transform (Hartley, 1942; Bracewell, 1990), that allows for the filtering of 1-D time series through the identification of the power at various spatial and temporal wavelengths. Its application to and the associated results are presented from its application to continuous Global Positioning System (GPS) data from southern California for the time period 1994 through 2006. The HL transform filter removes the high-frequency components of the data and effectively isolates the longer period signal. This long-period signal is modeled as time-dependent postseismic deformation using the viscoelastic-gravitational model of Fernández and Rundle (2004) for six stations selected for their proximity to the Northridge earthquake. The x-, y-, and z-components of the postseismic deformation are compared to the filtered data. Results suggest that this long-period deformation is a result of postseismic relaxation and that the HL transform filter provides an important new technique for the filtering of geophysical data consisting of the superposition of the effects of numerous complex sources at a variety of spatial and temporal scales.     

An Analytical Study for the Dispersion of Pollutants in a Finite Layer under Low Wind Conditions

A steady-state three-dimensional analytical model for the dispersion of a pollutant from a continuously emitting point source in a finite inversion layer has been proposed. The advection along the mean wind and the diffusion in all three directions have been accounted. A closed-form analytical solution of the proposed problem has been obtained using the method of integral transform and the same happens out to be non-Gaussian. Various limiting cases including the crosswind integrated concentration and the standard Gaussian-plume formula have been deduced from the solution obtained.The present model has been evaluated using Hanford diffusion experiment (DORAN et al., 1984) in stable conditions and IIT diffusion experiment (SINGH et al., 1991) in unstable conditions. The dispersion parameters have been computed using the various sigma schemes in accordance with the available observations. The proposed model has performed reasonably well with the data from both the diffusion experiments considered here.     

Rapid Earthquake Information for Bucharest

Advances in sensor techniques, digital acquisition, communication and computing allowed establishment of the field of real-time seismology (Kanamori et al., 1997) and the design of earthquake information systems that provide rapid information on ground motion and potential damage in an area for which a ground motion estimation data base is available and where the inventory of buildings and infrastructure and its vulnerability to shaking is known. We discuss a system for the Romanian capital of Bucharest, where an early warning system with about 30 seconds lead time, shake maps and a sophisticated damage estimation tool for Bucharest have been developed in the frame of the Collaborative Research Center on Strong Earthquakes ().     

Comparative analysis of sediment yield estimations using different empirical soil erosion models

The study aims to evaluate the performance of different empirical soil erosion models (EPM, USLE, Koutsoyiannis and Tarla, RUSLE) in mountainous Mediterranean-type catchments. The study area comprises the Arachthos, Kalamas, Upper Acheloos and Venetikos river basins, located in northwestern Greece. The methodology followed includes both qualitative and quantitative analyses. The former refers to the specific attributes of the models and the latter to the estimated sediment yield results. The results were initially validated against observed sediment yield values. The ambiguous reliability of such measurements led to their replacement by simulated ones, estimated using the sediment rating curve methodology. In the latter analysis, the models performed better, with more accurate results. Overall, the RUSLE corresponded best to such basins. Finally, the performance of seven empirical equations (Syvitski, Avendano Salas et al., Dendy and Bolton, Lu et al., Webb and Griffiths, Zarris et al.) was assessed, yielding relatively poor results.     

A Regional Archaeomagnetic Model for the Palaeointensity in Europe for the last 2000 Years and its Implications for Climatic Change

The SCHA.DI.00 directional model for the geomagnetic field in Europe for the last 2000 years (Pavón–Carrasco et al., 2008) has been updated by modelling the palaeointensity. This model, SCHA.DI.00, was developed from available Bayesian European Palaeosecular Variation Curves using the regional Spherical Cap Harmonic Analysis technique. The comparison of the palaeosecular variation curves, given by the regional model, with available archaeomagnetic data not used in its development showed an improvement with respect to the fit obtained by global archaeomagnetic models. In this paper advantage is taken of recently published palaeointensity databases to develop a complete (direction and intensity) regional archaeomagnetic model for the last 2000 years valid for the European region: the SCHA.DI.00–F model. Not only does this complete model provide an improvement for example for archaeomagnetic data studies, but it is also shown that this new regional model can be used to study the recently proposed link between the centennial secular variation of the geomagnetic field and climate change. The pattern of the archaeosecular variation of the field intensity obtained by SCHA.DI.00–F seems to verify the hypothesis presented by Gallet et al. (2005) about a possible (causal) connection between changes in the geomagnetic field intensity and in climate parameters, opening the door for more discussions on this challenging subject.     

Ergodicity in Natural Fault Systems

— Attempts to understand the physics of earthquakes over the past decade generally have focused on applying methods and theories developed based upon phase transitions, materials science, and percolation theory to a variety of numerical simulations of extended fault networks. This recent work suggests that fault systems can be interpreted as mean-field threshold systems in metastable equilibrium (Rundle et al., 1995; Klein et al., 1997; Ferguson et al., 1999), and that these results strongly support the view that seismic activity is highly correlated across many space and time scales within large volumes of the earth’s crust (Rundle et al., 2000; Tiampo et al., 2002). In these systems, the time averaged elastic energy of the system fluctuates around a constant value for some period of time and is punctuated by major events that reorder the system before it settles into another metastable energy well. One way to measure the stability of such a system is to check a quantity called the Thirumalai-Mountain (TM) energy metric (Thirumalai and Mountain, 1993; Klein et al., 1996). In particular, using this metric, we show that the actual California fault system is ergodic in space and time for the period in question, punctuated by the occurrence of large earthquakes, and that, for individual events in the system, there are correlated regions that are a subset of the larger fault network.     

Source Parameters for 1999 North Anatolian Fault Zone Aftershocks

We develop a data set of aftershock recordings of the 1999, M = 7.4 Izmit and M = 7.2 Duzce (Turkey) earthquakes to study their source parameters. We combined seismograms from 44 stations maintained by several sources (organizations) to obtain a unified data set of events (2.1 ≤ M_w ≤ 5.5). We calculate source parameters of these small earthquakes by two methods that use different techniques to address the difficulty in obtaining source spectra for small earthquakes subject to interference from site response. One method (program NetMoment (NM), Hutchings, 2004) uses spectra of direct S waves in a simultaneous inversion of local high-frequency network data to estimate seismic moment, source corner frequency (f_c), site attenuation (k) and whole-path Q. This approach takes advantage of the source commonality in all recordings for a particular earthquake by fitting a common Brune source spectrum to the data with a and individual k. The second approach (Mayeda et al., 2003) uses the coda method (CM) to obtain “nonmodel-based” source spectra and moment estimates from selected broadband recording sites. We found that both methods do well for events that allow the comparison with seismic moment estimates derived from waveform modeling. Also, source spectra obtained from the two methods are very closely matched for most of the events they have in common. We use an F test to examine the trade-off between k and f_c picks identified by the direct S-wave method. About half of the events could be constrained to have less than a 50% average uncertainty in f_c and k. We used these source spectra solutions to calculate energy and apparent stress and compare these to estimates from the selected “good quality” source spectra from CM. Both studies have values mutually consistent and show a similar increase in apparent stress with increasing moment. This result has added merit due to the independent approaches to calculate apparent stress. We conclude that both methods are at least partially validated by our study, and they both have usefulness for different circumstances of recording local small earthquakes. CM would work well in studies for which there is a broad magnitude range of events and NM works well for local events recorded by band-limited recorders.     

Statistical interpretation of the daily variation of urban water consumption in Beijing,China

Abstract

The efficient planning and design of water networks, as well as the management and strategies of existing water supply systems, require accurate short-term water demand forecasts. In this study, a statistical model for the estimation of daily urban water consumption was developed. The model was applied to analyse and forecast the daily water consumption in the main district of Beijing, China, from 2006 to 2010. The model exhibited good performance with a coefficient of determination, R², greater than 0.9 in both the calibration and validation periods. The results indicate that: (a) the 7-day moving average temperature is an efficient variable that can be used to depict water-use variation in a year; (b) a daily maximum temperature of 31.1°C and the occurrence of precipitation are two thresholds of water-use behaviour; and (c) the current day’s water consumption has a strong correlation with the consumption of one, two and seven days ago.

Editor Z.W. Kundzewicz; Associate editor D. Yang

Citation Zhang, D.W., et al., 2013. Statistical interpretation of the daily variation of urban water consumption in Beijing, China. Hydrological Sciences Journal, 59 (1), 181–192.     

Crust and Upper Mantle Structure in the Caribbean Region by Group Velocity Tomography and Regionalization

An overview of the crust and upper mantle structure of Central America and the Caribbean region is presented as a result of the processing of more than 200 seismograms recorded by digital broadband stations from SSSN and GSN seismic networks. Group velocity dispersion curves are obtained in the period range from 10s to 40s by FTAN analysis of the fundamental mode of the Rayleigh waves; the error of these measurements varies from 0.06 and 0.09 km/s. From the dispersion curve, seven tomographic maps at different periods and with average spatial resolution of 500 km are obtained. Using the logical combinatorial classification techniques, eight main groups of dispersion curves are determined from the tomographic maps and eleven main regions, each one characterized by one kind of dispersion curves, are identified. The average dispersion curves obtained for each region are extended to 150s by adding data from a larger-scale tomographic study (Vdovin et al., 1999) and inverted using a nonlinear procedure. A set of models of the S-wave velocity vs. depth in the crust and upper mantle is found as a result of the inversion process. In six regions we identify a typically oceanic crust and upper mantle structure, while in the other two the models are consistent with the presence of a continental structure. Two regions, located over the major geological zones of the accretionary crust of the Caribbean region, are characterized by a peculiar crust and upper mantle structure, indicating the presence of lithospheric roots reaching, at least, about 200 km of depth.     

An Independent Assessment of the Load/Unload Response Ratio (LURR) Proposed Method of Earthquake Prediction

The Load/Unload Response Ratio (LURR) method is a proposed technique to predict earthquakes that was first put forward by Yin (1987). LURR is based on the idea that when an area enters the damage regime, the rate of seismic activity during loading of the tidal cycle increases relative to the rate of seismic activity during unloading in the months to one year preceding a large earthquake. Since earth tides generally contribute the largest temporal variations in crustal stress, it seems plausible that earth tides would trigger earthquakes in areas that are close to failure (e.g., Vidale et al., 1998). However, the vast majority of studies have shown that earth tides do not trigger earthquakes (e.g., Vidale et al., 1998; Heaton, 1982; Rydelek et al., 1992). In this study, we conduct an independent test of the LURR method, since there would be important scientific and social implications if it were proven to be a robust method of earthquake prediction. Smith and Sammis (2004) undertook a similar study and found no evidence that there was predictive significance to the LURR method. We have repeated calculations of LURR for the Northridge earthquake in California, following both the parameters of X.C. Yin (personal communication) and the somewhat different ones of Smith and Sammis (2004). Though we have followed both sets of parameters closely, we have been unable to reproduce either set of results. Our examinations have shown that the LURR method is very sensitive to certain parameters. Thus it seems likely that the discrepancies between our results and those of previous studies are due to unaccounted for differences in the calculation parameters. A general agreement was made at the 2004 ACES Workshop in China between research groups studying LURR to work cooperatively to resolve the differences in methods and results, and thus permit more definitive conclusions on the potential usefulness of the LURR method in earthquake prediction.     

Frequency of dry and wet spells in san salvador

Summary A study of the daily rainfall in San Salvador (El Salvador) has been made over a thirty year period 1918–47 in order to determine the dry and wet spells. It has been found that the extreme dry spells on the Pacific Coast of Central America last longer than in other climates, examined byHuttary. The occurrence of a dry spell in San Salvador lasting over half a year is being minutely examined, and the cause of its origin traced to orographic effects during northerly winds.

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Resumen Se estudiaron las observaciones diaras de la precipitación en San Salvador (El Salvador), realizadas en los aňos 1918–47. Resulta que en la costa Pacifica Centroamericana los períodos secos duran más que los períodos más largos en los climas estudiados porHuttary. Un período seco que duró más de medio aňo en San Salvador se analiza detenidamente, se supone que éste se habría originado en influencias orográficas efectivos cuando hay viento del norte.

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Dr.Heinz Dieterichs, Jefe meteorólogo en el Servicio Meteorológico Nacional de El Salvador,San Salvador (El Salvador, Central America).     

Chemical and Isotopic Composition of Waters and Dissolved Gases in Some Thermal Springs of Sicily and Adjacent Volcanic Islands, Italy

Hydrochemical (major and some minor constituents), stable isotope ( and , δ13C_TDIC total dissolved inorganic carbon) and dissolved gas composition have been determined on 33 thermal discharges located throughout Sicily (Italy) and its adjacent islands. On the basis of major ion contents, four main water types have been distinguished: (1) a Na-Cl type; (2) a Ca-Mg > Na-SO₄-Cl type; (3) a Ca-Mg-HCO₃ type and (4) a Na-HCO₃ type water. Most waters are meteoric in origin or resulting from mixing between meteoric water and heavy-isotope end members. In some samples, δ¹⁸O values reflect the effects of equilibrium processes between thermal waters and rocks (positive ¹⁸O-shift) or thermal waters and CO₂ (negative ¹⁸O-shift). Dissolved gas composition indicates the occurrence of gas/water interaction processes in thermal aquifers. N₂/O₂ ratios higher than air-saturated water (ASW), suggest the presence of geochemical processes responsible for dissolved oxygen consumption. High CO₂ contents (more than 3000 cc/litre STP) dissolved in the thermal waters indicate the presence of an external source of carbon dioxide-rich gas. TDIC content and δ¹³C_TDIC show very large ranges from 4.6 to 145.3 mmol/Kg and from –10.0‰ and 2.8‰, respectively. Calculated values indicate the significant contribution from a deep source of carbon dioxide inorganic in origin. Interaction with Mediterranean magmatic CO₂ characterized by heavier carbon isotope ratios ( value from -3 to 0‰ vs V-PDB (CAPASSO et al., 1997, GIAMMANCO et al., 1998; INGUAGGIATO et al., 2000) with respect to MORB value and/or input of CO₂-derived from thermal decomposition of marine carbonates have been inferred.     

Quartz OSL sensitivity from dating data for provenance analysis of pleistocene and holocene fluvial sediments from lowland Amazonia

The properties of the quartz luminescence signal have been shown to be a useful tool for sediment provenance analysis. These provenance studies are based on the sensitivity of the fast optically stimulated luminescence (OSL) component, which is also used for sediment dating. Besides the widespread occurrence of quartz in terrigenous sediments, OSL sensitivity can be acquired using relatively fast and low-cost measurements compared to sediment provenance analysis methods based on accessory minerals or isotopes. Additionally, laboratories worldwide already have an extensive database of recorded quartz OSL signals primarily measured for dating studies, and these data could potentially be repurposed for provenance analysis of Quaternary sedimentary systems through OSL sensitivity calculation. Here, we investigate the use of OSL quartz signals measured in sediment dating surveys for OSL sensitivity calculation and evaluation of changes in sediment sources. The OSL sensitivity was calculated and expressed as %BOSL_F, which corresponds to the percentage of the fast OSL component signal (blue stimulation) to the total OSL curve; such approach is advantageous as it does not require any normalisation of the measured signal intensity to dose or aliquot size (weight). Three sets of samples from Amazonian fluvial sediments are investigated: two sets of Holocene floodplain sediments representing different sediment sources to the Amazonian fluvial system, i.e. the Amazon craton and the Andes Mountain belt, and a set of samples from the Içá Formation, a paleo-fluvial system active during the Pleistocene whose provenance is not fully known. Results show that the quartz OSL signal derived from the first test doses (T_n) applied in dating protocols had the best performance for %BOSL_F calculation when compared to results from a measurement protocol designed specifically for sediment provenance analysis. There is significant correlation (R² = 88) between sensitivities derived from T_n and a specific OSL provenance analysis protocol. The proposed approach indicates to be appropriate for sediment provenance analysis since it is able to discriminate signal differences among samples from known sources: Brazilian cratonic quartz yield high sensitivity values (mean %BOSL_F >70), in contrast to the relatively lower values from Andean quartz (mean %BOSL_F <50). In general, quartz OSL sensitivities from the Içá Formation samples fall into the same range of modern sediments transported by the Içá and Japurá rivers draining the Andean Eastern Cordillera of Colombia and Ecuador. We also observe a decrease in quartz OSL sensitivity during the Holocene, notably after 4 ka, with younger deposits showing lower sensitivity. Sediment provenance variations are discussed in terms of watershed rearrangement and/or precipitation-driven changes during the Late Pleistocene and Holocene across Amazonia.     

CodaQ as a combination of scattering and intrinsic attenuation: Numerical simulations with the boundary integral method

Numerical modelling ofSH wave seismograms in media whose material properties are prescribed by a random distribution of many perfectly elastic cavities and by intrinsic absorption of seismic energy (anelasticity) demonstrates that the main characteristics of the coda waves, namely amplitude decay and duration, are well described by singly scattered waves in anelastic media rather than by multiply scattered waves in either elastic or anelastic media. We use the Boundary Integral scheme developed byBenites et al. (1992) to compute the complete wave field and measure the values of the direct waveQ and coda wavesQ in a wide range of frequencies, determining the spatial decay of the direct wave log-amplitude relation and the temporal decay of the coda envelope, respectively. The effects of both intrinsic absorption and pure scattering on the overall attenuation can be quantified separately by computing theQ values for corresponding models with (anelastic) and without (elastic) absorption. For the models considered in this study, the values of codaQ ^–1 in anelastic media are in good agreement with the sum of the corresponding scatteringQ ^–1 and intrinsicQ ^–1 values, as established by the single-scattering model ofAki andChouet (1975). Also, for the same random model with intrinsic absorption it appears that the singly scattered waves propagate without significant loss of energy as compared with the multiply scattered waves, which are strongly affected by absorption, suggesting its dominant role in the attenuation of coda waves.     

Anisotropic velocity analysis1

Results from walkaway VSP and shale laboratory experiments show that shale anisotropy can be significantly anelliptic. Heterogeneity and anellipticity both lead to non-hyperbolic moveout curves and the resulting ambiguity in velocity analysis is investigated for the case of a factorizable anisotropic medium with a linear dependence of velocity on depth. More information can be obtained if there are several reflectors. The method of Dellinger et al. for anisotropic velocity analysis in layered transversely isotropic media is examined and is shown to be restricted to media having relatively small anellipticity. A new scheme, based on an expansion of the inverse-squared group velocity in spherical harmonics, is presented. This scheme can be used for larger anellipticity, and is applicable for horizontal layers having monoclinic symmetry with the symmetry plane parallel to the layers. The method is applied to invert the results of anisotropic ray tracing on a model Sand/shale sequence. For transversely isotropic media with small anisotropy, the scheme reduces to the method of Byun et al. and Byun and Corrigan. The expansion in spherical harmonics allows the P-phase slowness surface of each layer to be determined in analytic form from the layer parameters obtained by inversion without the need to assume that the anisotropy is weak.     

Some results on the approach of a slowly-varyng gravity wave to a beach

Abstract

Results from the theory of slowly-varying solutions of the non-linear shallow water equations (Varley et al. (1971)) are used to estimate maximum wave height amplifications on a beach of arbitrary shape. Carrier's solution (1966) for a large disturbance out at sea is used as input. Generalizations of the slowly-varying results to non-plane situations are also presented.     

On the Behavior of the Stable Boundary Layer and the Role of Initial Conditions

Previous studies of the stable atmospheric boundary layer using techniques of nonlinear dynamical systems (MCNIDER et al., 1995) have shown that the equations support multiple solutions in certain parameter spaces. When geostrophic speed is used as a bifurcation parameter, two stable equilibria are found—a warm solution corresponding to the high-wind regime where the surface layer of the atmosphere stays coupled to the outer layer, and a cold solution corresponding to the low-wind, decoupled case. Between the stable equilibria is an unstable region where multiple solutions exist. The bifurcation diagram is a classic S shape with the foldback region showing the multiple solutions. These studies were carried out using a simple two-layer model of the atmosphere with a fairly complete surface energy budget. This allowed the dynamical analysis to be carried out on a coupled set of four ordinary differential equations. The present paper extends this work by examining additional bifurcation parameters and, more importantly, analyzing a set of partial differential equations with full vertical dependence. Simple mathematical representations of classical problems in dynamical analysis often exhibit interesting behavior, such as multiple solutions, that is not retained in the behavior of more complete representations. In the present case the S-shaped bifurcation diagram remains with only slight variations from the two-layer model. For the parameter space in the foldback region, the evolution of the boundary layer may be dramatically affected by the initial conditions at sunset. An eigenvalue analysis carried out to determine whether the system might support pure limit-cycle behavior showed that purely complex eigenvalues are not found. Thus, any cyclic behavior is likely to be transient.     

Crustal model based on aeromagnetic profiles,gravity studies and wave velocities in rocks and crust

Summary Regional airborne magnetic profiles from India and U.S.A. are analyzed. Profiles are i) 130 km offshore Manglore to 60 km offshore Madras (India) along 13th parallel; ii) Washington to San Francisco (U.S.A.): iii) Brownsville (Texas) to Guatemala City (Mexico). Depth to the sources of magnetic anomalies along Manglore-Madras profile and Washington-San Francisco profiles is calculated either by elementary approximation ofSmellie or Prism model method ofVacquier et al. It is significant that depth values for some of the anomalies obtained by these methods are in very good agreement with those based on drilling data. The magnetic pictures along these profiles are compared with Bouguer gravity anomaly maps and it is shown that in almost all cases where magnetic bodies lie below 5 km (approximately) from sea level they are not reflected in gravity maps whereas all the magnetic bodies which are above 5 km (approximately) produce a markable feature in Bouguer gravity anomaly. This indicates that density of material below this level is almost equal to that of normal basic rocks (2.80 gm/cm³) and those above 5 km have a density less than this. Based on these results the top most layer in crust is considered to be metasedimentary including intrusive rocks and below this it is tentatively taken as Quartz-diorite accounting for the quartz rich Archean formations. Curves representing the variation of compressional wave velocity in i) granite; ii) quartz-diorite; iii) gabbro and iv) dunite, with pressure and temperature as reported from measurements in laboratory, are studied in the light of the general variation of P-wave velocity in the earth's crust reported from seismic sounding studies. It is found that a change in composition from metasedimentary zone to quartz diorite at about 5 km below sea level is supported by this study. It is found that further increase in compressional wave velocity in earth's crust can be explained by a compositional change from quartz diorite to gabbro. At certain places an unusual high velocity for compressional wave at the base of the crust is reported. This can be explained by considering that gabbro merges to Dunite in those areas. Based on this crustal model a probable explanation for the origin of granite masses is attempted.     

Seismic Records of the 2004 Sumatra and Other Tsunamis: A Quantitative Study

Following the recent reports by Yuan et al. (2005) of recordings of the 2004 Sumatra tsunami on the horizontal components of coastal seismometers in the Indian Ocean basin, we build a much enhanced dataset extending into the Atlantic and Pacific Oceans, as far away as Bermuda and Hawaii, and also expanded to five additional events in the years 1995–2006. In order to interpret these records quantitatively, we propose that the instruments are responding to the combination of horizontal displacement, tilt and perturbation in gravity described by Gilbert (1980), and induced by the passage of the progressive tsunami wave over the ocean basin. In this crude approximation, we simply ignore the island or continent structure, and assume that the seismometer functions de facto as an ocean-bottom instrument. The records can then be interpreted in the framework of tsunami normal mode theory,and lead to acceptable estimates of the seismic moment of the parent earthquakes. We further demonstrate the feasibility of deconvolving the response of the ocean floor in order to reconstruct the time series of the tsunami wave height at the surface of the ocean, suggesting that island or coastal continental seismometers could complement the function of tsunameters.