Spectral Ratio Data Research Articles

Confronting solutions of the Gallium Anomaly with reactor rate data

Recently, several models have been suggested to reduce the tension between Gallium and reactor antineutrino spectral ratio data which is found in the framework of 3+1 active-sterile neutrino mixing. Among these models, we consider the extensions of 3+1 mixing with a finite wavepacket size, or the decay of the heaviest neutrino ν4, or the possibility to have a broad ν4 mass distribution. We consider the reactor antineutrino rate data and we show that these models cannot eliminate the tension between Gallium and reactor rate data that is found in the 3+1 neutrino mixing framework. Indeed, we show that the parameter goodness of fit remains small. We consider also a model which explains the Gallium Anomaly with non-standard decoherence in the framework of three-neutrino mixing. We find that it is compatible with the reactor rate data.

Gallium Anomaly: critical view from the global picture of νe and {overline{nu}}_e disappearance

The significance of the Gallium Anomaly, from the BEST, GALLEX, and SAGE radioactive source experiments, is quantified using different theoretical calculations of the neutrino detection cross section, and its explanation due to neutrino oscillations is compared with the bounds from the analyses of reactor rate and spectral ratio data, β-decay data, and solar neutrino data. In the 3+1 active-sterile neutrino mixing scheme, the Gallium Anomaly is in strong tension with the individual and combined bounds of these data sets. In the combined scenario with all available data, the parameter goodness of fit is below 0.042%, corresponding to a severe tension of 4–5σ, or stronger. Therefore, we conclude that one should pursue other possible solutions beyond short-baseline oscillations for the Gallium Anomaly. We also present a new global fit of νe and {overline{nu}}_e disappearance data, showing that there is a 2.6–3.3σ preference in favor of short-baseline oscillations, which is driven by an updated analysis of reactor spectral ratio data.

Enhancement of convolutional neural network for urban environment parking space classification

BACKGROUND AND OBJECTIVES: Soil or rock properties where buildings are situated play an important role in the ground shaking caused by an earthquake. The highly populated Banda Aceh city in the northernmost Sumatra is flanked by two active faults, the Seulimeum and the Aceh segment. Therefore, it is crucial to investigate the subsurface characteristics of the region to reduce the earthquake risk as there was no regional study has been conducted so far.METHODS: Characteristics of the soil or rock of the subsurface were derived from various seismic parameters. The seismic microtremors were recorded at 36 sites covering the highly populated city and the two active faults. The spatial autocorrelation method was used to obtain a dispersion curve based on the relationship between seismic frequencies and phase velocity from triangular geophones array to determine the shear wave velocity of the subsurface layer. The seismic amplification, dominant frequency and vulnerability value at each measurement point were measured using the horizontal-to-vertical spectral ratio method. The maps of velocity structure and HVSR parameters were generated from the interpolation of those seismic parameters.FINDING: Based on the variation of the four geophysical parameters: shear wave velocity, seismic amplification, dominant frequency, and seismic vulnerability, the study area can be clustered into five different groups: I) Banda Aceh, II) Jantho, III) Krueng Raya, IV) Lhoknga-Lhoong, and V) Seulawah, which classify the different types of rocks. The classification of soil properties from the combination of shear wave and horizontal-to-vertical spectral ratio data correlates with the geology of the study area.CONCLUSION: The Banda Aceh city, flanked by the two active faults, is characterized by low shear wave velocity and high amplification because the city stands on the sedimentary basin; thus, it requires a detailed investigation prior to constructing infrastructures. The other clusters are located on the relatively less vulnerable areas, indicated by moderate shear wave velocity and moderate to low seismic vulnerability indexes. The joint analysis shows that the combination of physical properties, including the shear wave velocity, seismic amplification, and dominant frequency, can be used to investigate lithology and seismic vulnerability into a specific cluster. The research results are essential for hazard mitigation and can be used for disaster risk management by the local government. A detailed investigation with denser measurement points needs to be conducted to comprehensively describe the types of rocks in Banda Aceh and its surrounding.

Double-difference seismic attenuation tomography method and its application to The Geysers geothermal field, California

SUMMARY Knowledge of attenuation structure is important for understanding subsurface material properties. We have developed a double-difference seismic attenuation (DDQ) tomography method for high-resolution imaging of 3-D attenuation structure. Our method includes two main elements, the inversion of event-pair differential ${t^*}$ ($d{t^*}$) data and 3-D attenuation tomography with the $d{t^*}$ data. We developed a new spectral ratio method that jointly inverts spectral ratio data from pairs of events observed at a common set of stations to determine the $d{t^*}$ data. The spectral ratio method cancels out instrument and site response terms, resulting in more accurate $d{t^*}$ data compared to absolute ${t^*}$ from traditional methods using individual spectra. Synthetic tests show that the inversion of $d{t^*}$ data using our spectral ratio method is robust to the choice of source model and a moderate degree of noise. We modified an existing velocity tomography code so that it can invert $d{t^*}$ data for 3-D attenuation structure. We applied the new method to The Geyser geothermal field, California, which has vapour-dominated reservoirs and a long history of water injection. A new Qp model at The Geysers is determined using P-wave data of earthquakes in 2011, using our updated earthquake locations and Vp model. By taking advantage of more accurate $d{t^*}$ data and the cancellation of model uncertainties along the common paths outside of the source region, the DDQ tomography method achieves higher resolution, especially in the earthquake source regions, compared to the standard tomography method using ${t^*}$ data. This is validated by both the real and synthetic data tests. Our Qp and Vp models show consistent variations in a normal temperature reservoir that can be explained by variations in fracturing, permeability and fluid saturation and/or steam pressure. A prominent low-Qp and Vp zone associated with very active seismicity is imaged within a high temperature reservoir at depths below 2 km. This anomalous zone is likely partially saturated with injected fluids.

Seismic constraints on rock damaging related to a failing mountain peak: the Hochvogel, Allgäu

AbstractLarge rock slope failures play a pivotal role in long‐term landscape evolution and are a major concern in land use planning and hazard aspects. While the failure phase and the time immediately prior to failure are increasingly well studied, the nature of the preparation phase remains enigmatic. This knowledge gap is due, to a large degree, to difficulties associated with instrumenting high mountain terrain and the local nature of classic monitoring methods, which does not allow integral observation of large rock volumes. Here, we analyse data from a small network of up to seven seismic sensors installed during July–October 2018 (with 43 days of data loss) at the summit of the Hochvogel, a 2592 m high Alpine peak. We develop proxy time series indicative of cyclic and progressive changes of the summit. Modal analysis, horizontal‐to‐vertical spectral ratio data and end‐member modelling analysis reveal diurnal cycles of increasing and decreasing coupling stiffness of a 260,000 m3 large, instable rock volume, due to thermal forcing. Relative seismic wave velocity changes also indicate diurnal accumulation and release of stress within the rock mass. At longer time scales, there is a systematic superimposed pattern of stress increased over multiple days and episodic stress release within a few days, expressed in an increased emission of short seismic pulses indicative of rock cracking. Our data provide essential first order information on the development of large‐scale slope instabilities towards catastrophic failure. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.

Shallow Subsurface Structure in the Hualien Basin and Relevance to the Damage Pattern and Fault Rupture during the 2018 Hualien Earthquake

ABSTRACTThe 2018 Mw 6.4 Hualien earthquake generated a large peak-to-peak velocity of over 2 m/s, with a period of 3 s at the south end of the Milun fault, which resulted in the collapse of five buildings. To investigate the shallow subsurface soil structure and evaluate possible effects on the ground motion and building damage, we performed microtremor measurements in the Hualien basin. Based on the velocity structure jointly inverted from both Rayleigh-wave dispersion curves and microtremor horizontal-to-vertical spectral ratio data, we found that the shallow subsurface structure generally deepens from west to east. Close to the Milun fault, the structure becomes shallower, which is consistent with faulting during the 2018 earthquake and the long-term tectonic displacement. There is no significant variation for the site conditions in the north–south direction that can explain the large peak ground velocity in the south. As a result of the dense measurements in the heavily damaged area, where three high-rise buildings totally collapsed, these locations have the average S-wave velocity of the upper 30 m (AVS30) values and are relatively high compared to the more distant area from the Meilun River. This is somewhat unusual, because lower AVS30 values indicating softer ground conditions are expected close to the river. We did not find any characteristic subsurface soil structure that may contribute to the building collapses. The large 3 s pulse was probably generated by source effects, rather than subsurface soil amplification.

Site Characterization at Downhole Arrays by Joint Inversion of Dispersion Data and Acceleration Time Series

ABSTRACTWe present a sequential data assimilation algorithm based on the ensemble Kalman inversion to estimate the near-surface shear-wave velocity profile and damping; this is applicable when heterogeneous data and a priori information that can be represented in forms of (physical) equality and inequality constraints in the inverse problem are available. Although noninvasive methods, such as surface-wave testing, are efficient and cost-effective methods for inferring an VS profile, one should acknowledge that site characterization using inverse analyses can yield erroneous results associated with the lack of inverse problem uniqueness. One viable solution to alleviate the unsuitability of the inverse problem is to enrich the prior knowledge and/or the data space with complementary observations. In the case of noninvasive methods, the pertinent data are the dispersion curve of surface waves, typically resolved by means of active source methods at high frequencies and passive methods at low frequencies. To improve the inverse problem suitability, horizontal-to-vertical spectral ratio data are commonly used jointly with the dispersion data in the inversion. In this article, we show that the joint inversion of dispersion and strong-motion downhole array data can also reduce the margins of uncertainty in the VS profile estimation. This is because acceleration time series recorded at downhole arrays include both body and surface waves and therefore can enrich the observational data space in the inverse problem setting. We also show how the proposed algorithm can be modified to systematically incorporate physical constraints that further enhance its suitability. We use both synthetic and real data to examine the performance of the proposed framework in estimation of the VS profile and damping at the Garner Valley downhole array and compare them against the VS estimations in previous studies.

Development of Deep Shear Wave Velocity Profiles in the Canterbury Plains, New Zealand

Deep (typically > 1,000 m) shear wave velocity ( V S) profiles were developed across the Canterbury region of New Zealand at nine strong-motion stations using a combination of active and passive surface wave methods. A multimode, multimethod joint inversion process, which included Rayleigh and Love wave dispersion and horizontal-to-vertical spectral ratio data, was used to develop the V S profiles at each site. A priori geologic information was used in defining preliminary constraints on the complex geologic layering of the deep basin underlying the region, including velocity reversals in locations where interbedded terrestrial gravels and marine sediments are present. Shear wave profiles developed as part of this study had characteristics comparable to the profiles from 14 Christchurch sites detailed in a separate study. The profiles developed in the two studies were combined to form region-specific V S profiles for typical deposits, which can be used to improve the accuracy of current three-dimensional (3-D) crustal velocity models of the region.

Mapping cover-thickness to UNCOVER basement and deep Earth architecture and processes

Under the UNCOVER initiative it is generally accepted that construction of accurate cover-thickness maps is the most tractable and urgent means of facilitating resource exploration under cover. To meet this goal we have been undertaking benchmarking of various geophysical techniques, constructing a national database of Estimates of Geological and Geophysical Surfaces (EGGS) to store legacy estimates and developing machine learning algorithms to interpolate between these estimates. Benchmarking magnetic top estimates to ~700 drill sites across the Murray Basin highlights the importance of performing estimates using profile data as opposed to grids. Inversion of horizontal to vertical spectral ratio data, derived from single broadband seismometers, reveals surprisingly robust cover-thickness estimates. While these insights are directly relevant in supporting drilling programs they can also be used to constrain deep Earth architecture and processes. We show that inversion of basin subsidence data can be used to constrain lithospheric thickness and mapped chrono-stratigraphic surfaces can be used to test models of uplift of the Australian continent related to convective flow within the Earth’s mantle.

Shear-wave Velocity Profile for Holocene Sediments Measured from Microtremor Array Studies, SCPT, and Seismic Refraction

The microtremor method was trialed on soft Holocene sediments overlying glacial gravels near the Hutt River, Wellington New Zealand. A triangular four-station array of radius [Formula: see text], processed using a modified spatial autocorrelation (SPAC) method was sufficient to establish shear velocity for sediments and gravels, and a thickness of [Formula: see text] for the soft sediments. The interpretation was performed blind to geological and geophysical data, and subsequent comparison with seismic cone penetrometer and seismic refraction data shows the accuracy from the SPAC interpretation to be better than 5%. Interpretation of horizontal: vertical spectral ratio data assists with estimates of thickness of the glacial gravels (hundreds of meters) but accuracy in thickness is poor, perhaps due to uncertainty in the 2D nature of the base of the gravel-filled glacial valley.

Use of empirical Green's functions, spectral ratios, and kinematic source models for simulating strong ground motion

AbstractGround motions for large and moderately large earthquakes at short and moderate distances are particularly important for seismic hazard estimation in eastern North America (ENA). Very few direct observations of such ground motions have been obtained, however, because of the sparsity of recording sites and the relatively low rates of occurrence of large earthquakes inside the region. Estimation of strong ground motion must therefore rely heavily on theoretical models to extend empirical results obtained from small earthquakes and from the few larger ones for which reliable data are available. Because of the generally large distances between recording stations, the main source of useful data comes from Lg wave trains observed at relatively large distances. For the two largest earthquakes to have occurred near populated regions of southeastern Canada during the past decade, spectral ratios of the Lg wave trains of the mainshocks, with respect to those of their aftershocks, are found to depend almost entirely upon the source radiation characteristics of the sources alone. This result is utilized to derive elastodynamically-based kinematic rupture models that are consistent with the empirical spectral ratio data. Such models provide a firm physical basis from which to infer the most probable spectral characteristics for future large earthquakes in the region. In converse application, it is shown that spectral ratios obtained from such models, along with empirical seismograms from small earthquakes, can be used to accurately simulate strong ground motions at short and moderate (as well as large) distances. As such small-event seismograms are relatively plentiful, the problem of reliable strong ground motion estimation is therefore reduced to that of obtaining reliable representative source spectral models. The solution of this latter problem must continue to depend upon whatever empirical data are available and upon appropriately detailed theoretical modeling.

High-frequency borehole seismograms recorded in the San Jcinto Fault zone, Southern California Part 2. Attenuation and site effects

AbstractWe examine surface and downhole P- and S-wave spectra from local earthquakes recorded at two borehole seismometer arrays (KNW-BH and PFO-BH) installed in the Southern California Batholith region of the San Jacinto Fault zone by the U.S. Geological Survey to assess the influence of the weathered layer on the spectral content of high-frequency (2 to 200 Hz) seismic signals.Earthquake signals recorded downhole at both sites show significantly improved seismic bandwidth due to both a reduction in ambient noise levels and (especially) to dramatically increased levels of high-frequency signal. Significant seismic signal is observed up to approximately 190 Hz for P waves at KNW-BH. Stacked spectral ratios from these signals indicate that the highly weathered near-surface (between 0 and 150 m) at KNW-BH and PFO-BH exerts a much larger influence on seismic signals than deeper (between 150 and 300 m) material. Modeling of uphole/downhole spectral ratio data suggests Qα ≈ 6.5 and Qβ ≈ 9 between 0 and 150 m, increasing to Qα ≈ 27 and Qβ ≳ 26 between 150 and 300 m. An outcrop-mounted Anza network station, deployed approximately 0.4 km from KNW-BH, displays roughly similar high-frequency content to the KNW-BH downhole sensors, but it exhibits spectra that are significantly colored by directional resonances.Low-Q and low-velocity near-surface material forms a lossy boundary layer at these borehole sites that is advantageous to the high-frequency downhole environment; not only are noise levels reduced, but reflections from the surface and near-surface are greatly attenuated. As a result, high-frequency recordings from below the weathered zone more nearly resemble those recorded in a whole space than would otherwise be expected.

An analysis of spectral differences between Nevada Test Site and Shagan River nuclear explosions

Spectral ratio discrimination studies carried out on events located in the western United States and Soviet Union (S.U.) illustrate that pronounced differences in radiated explosion‐source spectra relative to nearby earthquakes exist between the two regions. Nevada Test Site (NTS) explosions are characterized by the existence of more low‐frequency and/or less high‐frequency energy (greater low‐to high‐frequency spectral ratios) than western U.S. earthquakes. The opposite pattern is observed in the S.U. with nuclear explosions appearing to have more high‐frequency (and/or less low‐frequency) energy than earthquakes. These observations may be caused by at least two principal effects that are probably acting in parallel: (1) variations in depth‐dependent effects of attenuation acting between the shallow explosions and deeper earthquakes and (2) differences in the dynamic response of the near‐source geology to the passing explosion shock wave. Anelastic synthetic seismogram calculations illustrate that depth‐dependent attenuation effects may explain the spectral observations. However, a number of observations using near‐ and far‐field data from NTS explosions suggest that near‐source effects are the dominant factor. A quasi‐empirical explosion source model is proposed that simultaneously fits the spectral ratio data from both the U.S. and S.U. relative to earthquakes in each of the respective regions. Additionally, the model fits the trends of the spectral ratios observed as a function of magnitude. The key to the model is the shape of the pressure time history acting at the elastic radius. For explosions detonated in weak, porous rock, the radiated shock wave divides into a two‐wave system consisting of an elastic precursor followed by a plastic wave. The generation of this two‐wave system introduces a rise time into the pressure time history. In the frequency domain a second corner frequency is established in a third‐order model (with an ω−3 high‐frequency decay) whose value is inversely proportional to the time separation of the two waves. In higher‐strength, saturated rocks (or for overburied explosions) the effective rise time is short, and a second‐order model is appropriate (with an ω−2 high‐frequency decay). The second‐order model provides a good fit to the S.U. data. In contrast, a hybrid model is required to fit the NTS data with an ω−3 high‐frequency decay for shallow explosions detonated in unsaturated tuff that evolves to an ω−2 decay as depth of burials reach higher‐strength, saturated rocks below the water table.

Near-surface velocities and attenuation at two boreholes near Anza, California, from logging data

AbstractTo investigate near-surface site effects in granite rock, we drilled 300-m-deep boreholes at two sites which are collocated with stations from the digital array at Anza, California. The first borehole was sited at station KNW (Keenwild fire station), which is located along a ridge line about 8.7 km east of the San Jacinto Fault zone. Station PFO (Piñon Flat Observatory), chosen for the second site, is another 6 km further to the east of station KNW and is located on a gently sloping hillside. We logged each borehole for P- and S-wave velocities, as well as for crack density and orientation.P waves were generated by striking a plate with a hammer at the surface. A tool consisting of weighted anvils driven by compressed air against end plates along a 3.5-m beam was used to generate shear waves. Signals were recorded downhole with a three-component sensor package at 2.5-m intervals from the surface to 50 m depth, and at 5-m intervals from 50 m depth to the bottom of the hole. Velocities were determined by differencing the measured arrival times of first arrivals or peaks over each interval in depth. Travel times were computed for the first breaks at shallow depths, however, below about 100 m depth, times were computed for the first peaks rather than for first breaks since the first arrival was no longer clearly distinguishable. The KNW site yielded a shear velocity of 1.9 km/sec by only 30 m in depth and reached close to 2.6 km/sec at the bottom of the hole. P-wave velocities at KNW were also high at 5.4 km/sec starting at 120 m depth. The PFO site had similar but slightly higher shear-wave velocities. The bottom-hole shear-wave velocity reached 3.0 km/sec, and the P-wave velocity was 5.4 km/sec.Shear-wave attenuation was computed using both the pulse rise time and spectral ratio methods. At station KNW, attenuation was significant only in an interval between 17.5 and approximately 40 m in depth. Over the top 50 m, attenuation corresponding to a Q of about 8 was obtained. A total T* of 0.004 sec was measured for this interval. Pulse rise times also increased rapidly in this zone. The spectral ratio data for station PFO yields two peaks in attenuation above 50 m. Similar to the attenuation found for station KNW, the peak in attenuation corresponds to a Q of about 11, averaged over the top 50 m. Spectra of the seismic pulses produced by the hammer give good signal between 20 to 80 Hz.Significant motion perpendicular to the polarizations of the first shear-wave arrival was recorded within a few meters of the surface. Apparently, the rock structure is sufficiently complicated that body waves are being converted (SH to SV at oblique incidence) very close to the surface. The presence of these elliptical particle motions within a mere few m of the pure shear-wave source suggests that the detection of polarizations perpendicular to the main shear arrival at a single location at the surface is not, by itself, a good method for detecting shearwave splitting within the upper few tens of kilometers of the earth's crust.Crack densities and orientations were determined from televiewer records. These records showed cracks with a preferred direction at station KNW and of a greater density than at station PFO. At station PFO, crack densities were smaller and more diffuse in orientation.

Short-period PKP phases and the anelastic mechanism of the inner core

Short-period seismograms are synthesized for PKP phases in anelastic Earth models. The synthetics were constructed using a synthetic technique valid at grazing incidence, a source-time function appropriate for deep-focus earthquakes, and an instrument response for either a short-period WWSSN or SRO seismograph. The agreement between predicted and observed amplitudes and spectral ratios requires neither a low- Q α zone at 0.2–2 Hz nor a low or negative P-velocity gradient at the bottom of the outer core. Thin low- Q α zones beneath the inner core boundary fit spectral ratio data that sample the upper 200 km of the inner core but fail to fit data that sample the lower inner core. Only a model having Q α −1 ϵ[0.003, 0.004] at 0.2–2 Hz, nearly constant with depth in the inner core, satisfies all of the spectral ratio and amplitude data. The assumption of a bulk viscosity of 10-10 3 Pa s for the liquid phase of a partially molten inner core combined with the observation of low shear attenuation in the inner core at frequencies less than 0.005 Hz limit the physical parameters associated with two possible attenuation mechanisms: (1) fluid flow and viscous relaxation due to ellipsoidally shaped inclusions of melt, and (2) the solid-liquid phase transformation induced by the stress change during the passage of a seismic wave. Both mechanisms require an order of 0.1% partial melt to reproduce the observed Q α −1. In the outer core, the time constant of the mechanism of phase transformation is predicted to be 10 4–10 6 s. Confirmation of small shear attenuation in the inner core in the frequency band of seismic body waves would favor the mechanism of phase transformation.