Distinct Arrivals Research Articles

Atmospheric model inversion using infrasound signals from the North Korean underground nuclear explosion and the subsequent collapse event in 2017

SUMMARY This study focuses on the infrasound signals from the September 2017 North Korean underground nuclear explosion (UNE17) and subsequent collapse event (SCE17) that occurred close to the autumnal equinox when the atmospheric temperature structure undergoes rapid change. Multiple arrivals, including contributions from local, diffracted and epicentral infrasound, generated by UNE17, were observed at eight infrasound arrays in the Korean Peninsula and one IMS infrasound station (IS45) in Russia while at the closest five arrays for SCE17 only epicentral infrasound was observed. The UNE17 signals provide the opportunity to explore the utility of each distinct arrival in constraining atmospheric conditions during the change associated with the equinox. The observed characteristics of the multiple epicentral infrasonic phases (celerity, backazimuth, phase velocity and spectra) suggest propagation paths through the tropospheric, stratospheric and thermospheric waveguides, although geometric ray paths based on a global atmospheric model at the time of the explosion predict only thermospheric returns. The absence of predicted stratospheric returns may reflect errors in the atmospheric models due to the lack of predicted stratospheric winds which are weak and changing close to the autumnal equinox or the limited resolution of the fine-scale structure not captured by current atmospheric models. The differences between the model predictions and the observations suggest that the numerical weather forecast models need to be modified to fully explain the observations. In order to explore the model space that can explain the UNE17 data set, an inversion scheme is applied to atmospheric wind model parameters constrained by the multi-array observations. Zonal and meridional wind profiles are parametrized using empirical orthogonal functions (EOFs) estimated from 1-yr of Ground-to-Space atmospheric specifications. A best-fitting atmospheric model is estimated using a Bayesian approach that assesses the uncertainty in the inverse solution using a joint likelihood function combining components of azimuth deviation, traveltime and phase velocity. The updated atmospheric models from six different EOFs inversions have up to 20 m s–1 stronger zonal and meridional wind speeds in the stratosphere compared to the original model, and explain the stratospheric observations in the data set. This investigation illustrates that modest changes to atmospheric wind models at the time of autumnal equinox can improve the prediction of stratospheric returns.

Comparison of two distinct arrival and treatment programs for bovine respiratory disease in high-risk feeder cattle entering a feedlot.

Antimicrobial metaphylaxis of high-risk cattle entering the feedlot is a common management strategy implemented against bovine respiratory disease (BRD). Typically, following a prescribed postmetaphylactic interval (PMI), animals displaying clinical signs of BRD are pulled from the feedlot pen and treated with antimicrobials when treatment criteria are met. The objective of this study was to compare 2 distinct sequential BRD treatment protocols each consisting of a metaphylactic antimicrobial plus 2 potential subsequent as-needed treatment antimicrobials. Heifers at high-risk for BRD (n = 1000; initial BW = 229 kg ± 1.6) purchased from sale barns in the southeastern U.S. were transported to a contract research feedlot in Nebraska and randomly assigned to 1 of 2 experimental groups (10 blocks of 100 animals each; 50 per treatment group). Experimental groups consisted of: (1) tulathromycin metaphylaxis (2.5 mg/kg) followed by ceftiofur crystalline free acid (6.6 mg/kg) and danofloxacin (8 mg/kg) for subsequent first and second as-needed BRD treatment, respectively (TCD) or (2) tildipirosin metaphylaxis (4 mg/kg) followed by florfenicol-flunixin meglumine (40 mg/kg florfenicol; 2.2 mg/kg flunixin meglumine) and enrofloxacin (12.5 mg/kg) for subsequent first and second as-needed BRD treatment, respectively (TFFE). Following expiration of the 7-d PMI, calves that showed signs of clinical BRD were pulled and examined to determine if treatment was necessary based on a clinical attitude score (CAS). Heifers with a CAS of 1 accompanied by ≥40°C rectal temperature, and all heifers with a CAS ≥ 2 regardless of rectal temperature, received the appropriate first-treatment antimicrobial. Upon relapse, following expiration of the post-treatment interval (PTI), heifers received the appropriate second-treatment antimicrobial. In the first 90 d, calves in the TFFE experimental group received more first-treatments than calves in the TCD experimental group (P = 0.054) and resulted in 50% greater mortality (P < 0.043) relative to the TCD heifers. From d 0 to closeout, first-treatment morbidity as well as mortality were greater in TFFE relative to TCD (P ≤ 0.032). Growth performance did not differ between treatments in the first 90 d; however, ADG was greater (P = 0.033) and G:F improved (P = 0.014) at closeout in TCD versus TFFE on a deads-in basis. Closeout economics revealed a $50.78/animal greater profit in the TCD experimental group relative to TFFE.

Vector sensor measurements of dispersed arrivals from explosive signals, underwater sound (SUS)

In 2017 and 2021, ONR experiments south of New England examined the effect of the environment on sound propagation. A series of small explosive ordinance called SUS, models Mk-64 (1.1 oz) and Mk-82 (1.8 lbs), were deployed at various ranges (1-40 km) from a vector sensor positioned a 1.5 m above the seafloor. These studies focused on two areas: (1) the New England Mud Patch (NEMP) where 75 m of water overlay a thick 10-m layer of surficial mud; (2) a 60 km south-southwest of the NEMP where the continental shelf transitions to the slope. SUS provide a strong impulse signal, exciting both water-borne and sediment-borne arrivals. Owing to geometric dispersion, a time-frequency representation of the signals reveal distinct arrivals associated with the propagating normal modes. Forward models based on mode theory are presented to demonstrate the effects of bathymetry, oceanography and sediment structure on dispersed SUS signals. The model facilitates both the extraction of vector information, and inverting it to determine geo-acoustic properties of the environment. Measured vector data are also presented, including examples on the continental slope where the 3D propagation effects encountered will need to be considered for successful modeling and inversion.

A Possible Role of Pulegone against Glypican-1 for the Treatment of Alzheimer’s Disease through In-Silico Approach

Alzheimer’s disease (AD) dementia is a type of neurodegenerative disease, refers to a distinct arrival and certainly functional and mental decline which is linked with age which eventually leads to death. This current study was to demonstrate the role of pulegone against Glypican-1 for the treatment of Alzheimer’s disease through an in-silico approach. Methods: All the information and studies were gleaned from molecular docking. With the use of docking software, Docking was implemented between the target protein GPC1 (PDB ID: 4YWT) and the entire ligands. We preferred GPC1 (PDB ID: 4YWT) as a target protein and several natural compounds such as Rosmarinic acid, Allo ocimene, and Pulegone as ligands. When the preparation of protein is done, in PyRx software we introduced the entire ligand for the process of virtual screening. As reported by the result of PyRx and Lipinski’s Rule of Five, the finest compound against GPC1 with its smallest amount of binding energy was Pulegone. Results: For the procedure of molecular docking between the receptor protein GPC1 (PDB ID: 4YWT) and Pulegone a software called AutoDock Vina was used. The outcome showed 9 poses with distinct binding energy, RMSD LB (Root means square deviation Lower Bound), RMSD UB (Root mean square deviation Upper Bound). Through PyMol (an open-access tool for the visualization of the molecule), the interaction amidst Pulegone and GPC1 can be visualized. Conclusion: The merely compound which can restrain the activity of GPC1 (PDB ID: 4YWT) was Pulegone, based on the in-silico approach. Therefore in the advanced studies, Pulegone can be a capable medicine acquired from natural sources for dealing with Alzheimer’s disease.

Multipath Broadband Localization, Bathymetry, and Sediment Inversion

Transmission of linearly frequency modulated pulses generates receptions at a vertical line array that can be cross correlated with the source signal to provide estimates of the oceanic waveguide impulse response. For short ranges, distinct path arrivals can be identified including the direct, surface reflection, bottom reflection, and sediment reflection. Accurate estimation of arrival times of such paths is tightly related to successful inversion for source location and water column depth and sound speed and, subsequently, estimation of sediment sound speed and thickness. To achieve accurate estimation, particle filtering is applied to the received time series at 16 phones combined with a simple cross-correlation method. Using linearization, arrival time probability density functions are connected to the geometry and water column sound-speed parameters, providing point estimates as well as probability densities. These are then employed in sediment sound speed and thickness estimation. The results, obtained from the application of the method to data collected during the Seabed Characterization Experiment, are consistent with prior information on the site.

Evolution of the correlation wavefield extracted from seismic event coda

The seismic correlation wavefield constructed from stacked cross-correlograms of event signals displays a wide range of features as a function of inter-station distance. The character of such correlation arrivals changes markedly with the segment of the wavefield employed. All such correlation arrivals arise from the interaction of seismic phases that have a common slowness at the pair of stations being correlated. It takes some time before a clear correlation field is established, but after 1 h from event initiation a weak version of the regular wavefield emerges accompanied by many phases that have no counterpart in the direct source excitation. Such arrivals are produced by the interaction of seismic phases with common propagation legs, and have time-distance behaviour controlled by the differences in accumulated phase. The regular phases fade with time and then distinct arrivals in the correlation field arise when there are many ways in which combinations of seismic phases have the same difference in propagation legs. There are many more such possibilities for steeply travelling waves in the late coda, so that a relatively stable correlation field develops. The properties of the correlation field as a function of time can be well described by using a representation in terms of generalized rays supplemented by the contribution from the fundamental mode Rayleigh wave.

The nature of Earth's correlation wavefield: late coda of large earthquakes

The seismic correlation wavefield constructed from the stacked cross-correlograms of the late coda of earthquake signals at stations across the globe provides a wealth of observed pulses as a function of inter-station distance. The interval from 3 to 10 h after the onset of major earthquakes is employed for the period range from 15 to 50 s. The observations can be well matched by synthetic seismograms for a radially stratified Earth. Many of the correlation phases have similar time behaviour to those in the regular wavefield, but others have no correspondence. All such correlation phases can be explained by the interaction of arrivals with a common slowness at the each of the stations being correlated. Using a generalized ray description of the seismic wavefield, the time-distance behaviour of these correlation phases arises from differences in accumulated phase on different propagation paths through the Earth. Distinct arrivals emerge from the correlation field when there are many ways in which combinations of seismic phases can arise with the same difference in propagation legs. The constituents of the late coda are dominated by steeply travelling waves, and in consequence features associated with multiple passages through the whole Earth emerge distinctly, such as high-order multiples of PKIKP .

Extended wave-equation imaging conditions for passive seismic data

The information obtained from seismic monitoring at injection sites is often limited to seismic event properties (e.g., location, origin time, moment tensor), the accuracy of which greatly depends on the assumed or estimated elastic velocity models. Current traveltime-based methods to calibrate velocity models rely on having distinct arrivals. In surface seismic monitoring, however, the signal-to-noise ratio of arrivals is often too poor for pick-based methods, and migration techniques are needed. Wave-equation migration can image microseismic sources without the need for picking or knowledge of the onset time by reconstructing the wavefield through the model space and applying an imaging condition. We have devised extended imaging conditions for passive seismic wave-equation imaging algorithms, and we have found that they represent a key step toward verifying and updating elastic velocity models. By extending imaging conditions away from zero lag in time and space, we can better evaluate the focusing of a given event based on a self-consistency principle that direct arrival waves focus at zero lag only when the velocity models were correct. We have determined that given an elastic medium and multicomponent recordings, we can propagate and correlate microseismic P- and S-wavefield modes to compute extended imaging conditions that are sensitive to P- and S-wave velocity perturbations. The extended image volume is robust to sparsely sampled data and high levels of noise and is sensitive to velocity model errors. The extended image volume can be used to determine relative P- and S-wave velocity updates to improve focusing.

Persistent shallow background microseismicity on Hekla volcano, Iceland: A potential monitoring tool

Hekla is one of Iceland's most active volcanoes. Since 1970 it has erupted four times with a period of quiescence of 14years since the last eruption. We detected persistent levels of background microseismicity with a temporary seismic network in autumn 2012. An amplitude based as well as an arrival-time based location method was applied to two populations of events and located them at shallow depths on the northern flank, close to the summit. This seismicity has not been identified previously by the permanent seismic network in Iceland as it is below its detection threshold. The detected events were either short, higher frequency events with distinct arrivals located beneath the summit on the northern flank of Hekla or longer, emergent, lower frequency events about 4km northeast of the summit at 200–400m depth below the surface. Estimated moment magnitudes were MW=-1.1 to -0.1 and MW=-0.9 to -0.0 and local magnitudes ML=-0.5 to +0.3 and ML=-0.3 to +0.3, respectively. This seismicity does not show any correlation with gas output but is located at the steepest slopes of the edifice. Hence we suggest that the current shallow microseismicity at Hekla is structurally controlled. This offers a possible opportunity of using near summit microseismicity as a tool for monitoring emerging unrest at Hekla. Microseismicity rates will be very sensitive to small stress perturbations due to magma migration at depth. Currently in the absence of microseismicity monitoring, Hekla switches from apparently quiescent to fully eruptive on the order of only 1h.

Impulse propagation in the nocturnal boundary layer: Analysis of the geometric component

On clear dry nights over flat land, a temperature inversion and stable nocturnal wind jet lead to an acoustic duct in the lowest few hundred meters of the atmosphere. An impulsive signal propagating in such a duct is received at long ranges from the source as an extended wave train consisting of a series of weakly dispersed distinct arrivals followed by a strongly dispersed low-frequency tail. The leading distinct arrivals have been previously shown to be well modeled by geometric acoustics. In this paper, the geometric acoustics approximation for the leading arrivals is investigated. Using the solutions of the eikonal and transport equations, travel times, amplitudes, and caustic structures of the distinct arrivals have been determined. The time delay between and relative amplitudes of the direct-refracted and single ground reflection arrivals have been investigated as parameters for an inversion scheme. A two parameter quadratic approximation to the effective sound speed profile has been fit and found to be in strong agreement with meteorological measurements from the time of propagation.

Depth-Recursive Tomography of the Bohemian Massif at the CEL09 Transect—Part A: Resolution Estimates and Deblurring Aspects

The refraction CEL09 profile from the CELEBRATION 2000 project intersects the main terranes of the Bohemian Massif in the NW–SE direction: the Saxothuringian, the Tepla-Barrandian, the Moldanubian and the Moravo-Silesian. In its easternmost part, it crosses the Western Outer Carpathians overthrust westward onto the Bohemian Massif. Only the first 450 km were surveyed with the densest deployment of shot points providing data suitable for a reliable geological interpretation. The first-arrival depth-recursive tomography was applied here to derive a P-wave velocity image of the upper and middle crust (Part A). The proper interpretation of the obtained velocity features is the subject of the accompanying paper (Part B). The attained resolution in the velocity image is shown to be superior as compared with the previous CEL09 models based also on the more uncertain later arrivals of reflection waves. The applied DRTG (depth-recursive tomography on grid) method is based on a regular network of refraction grid rays generated for iteratively updated starting models. Only the distinct first arrivals with minimum uncertainty are used for the DRTG inversions to yield the maximum resolution. Thanks to the full control of the data fit by the grid rays used, the statistical lateral resolution could be determined at single grid depths for the chosen confidence levels. Thus, the lateral sizes of the anomalies that can be yet resolved are determined in dependence on their depths and their velocity excesses. The defocusing of the imaged features is studied on the basis of the spatial responses to spike excitation. The calculated spatial responses also allowed the edge smearing of the velocity anomalies to be assessed. Special attention is paid to the imaging of low-velocity zones that are usually suppressed by the smoothing measures used in standard tomographic methods. An improvement was achieved if the smoothing was suggested with regard to the occurrence of the low-velocity zones repeatedly appearing in higher iterations. The gained deblurring effect concerns both the negative and positive anomalies as documented on the velocity features interpreted in the accompanying paper.

Using relative amplitude and travel times from geometric acoustics to determine nocturnal effective sound speeds.

On clear dry nights over flat land, a temperature inversion and stable nocturnal wind structure lead to an acoustic duct in the lowest few hundred meters of the atmosphere. An impulsive signal undergoes strong dispersion during propagation and is received at long ranges from the source as an extended wave train consisting of a series of distinct arrivals followed by a low frequency tail. The leading distinct arrivals have been shown to coincide with the direct and single reflection geometric ray paths. At a range of 2 Km from the source, these ray paths propagate through the lowest 50–70 m of the atmosphere while larger range arrivals reach higher into the atmosphere. Using the solutions of the eikonal and transport equations, travel times, amplitudes, and caustic structures of the arrivals can be determined. Arrival details can then be used to fit a low order Taylor series expansion of the effective sound speed profile. Approximations of the atmospheric conditions in the duct will be presented along with both predicted and measured arrival waveforms and meteorological data from the time of propagation.

Some Notes on Discrete Trains of Infrasonic Waves Produced by Point Sources

The most prominent trains of infrasonic waves are produced by strong point disturbances in the atmosphere, such as nuclear explosions in the megaton range. The infrasonic records at the La Paz Bolivia observatory indicate that the signals resulting from such explosions have a sharp beginning similar to seismic records. The results of analysing the data from four signals presumed to have resulted from nuclear explosions in the atmosphere are given in Table 1. The great circle path length from the source location to La Paz, and the arrival times for the short and long path arrivals are also given in the table. The long path arrival for all events, except that of 1968 August 24, was somewhat masked by the irregular noise at the tail of the short path signal. Readings on all received signals were taken at four distinct times. Values are not given for some readings on the long path arrivals, due to low signal conditions. The periods given in the table indicate normal dispersion properties, with the very long period gravity waves arriving first. The remaining readings appear irregular both in period and in travel time, with no distinct wave arrivals noted. The observed dispersion is somewhat dependent on the size of the explosion exciting the waves, but a greater influence is the wind and temperature variation with altitude. Seasonal effects are evidenced by observing the travel time for the events of 1968 December 27 and 1970 October 14. The difference between the short and long path arrivals is changing, probably due to different seasonal wind profiles.

Observations of micromultipath formation at very long ranges in shallow water.

Long- and very-long-range shallow-water transmission is observed for low-frequency m-sequences transmissions with center frequencies of 50, 100, and 250 Hz. The source is suspended from a ship that is holding position at each of three ranges: 10, 20, and 80 km. The receiver is a bottomed horizontal array. The array is used to resolve out-of-plane arrival angles to a small fraction of a degree by observing phase rolls of the spatial coherence function of the various arriving wavefronts. At the 10 and 20 km ranges, distinct pulse arrivals are observed in one-to-one correspondence to normal mode arrivals predicted with PE propagation models. But at the 80 km range, a large number of distinct arrivals appear with intensities or arrival times inconsistent with deterministic normal mode or ray arrivals. One possibility is that these are micromultipaths from out-of-plane paths after reflections from facets or sloping bottom contours. In fact, each of the arrivals has a unique horizontal arrival angle, and the steeper the out-of-plane angle, the later the arrival—an observation that is verified with broadband PE propagation model computations for both random faceted and gently sloping bottoms.

On the fast arrivals seen in impulse propagation in the nocturnal boundary layer.

On clear dry nights over flat land, an acoustic duct forms in the atmospheric boundary layer. The duct is formed by a temperature inversion in the lowest few hundred m of the atmosphere and by the stiff wind, known as the nocturnal jet, which commonly develops above the temperature inversion. An impulsive signal undergoes strong dispersion as it propagates in the nocturnal duct and is received at long ranges from the source as an extended wave train consisting of a series of distinct arrivals followed finally by a low frequency tail. The first arrival is of interest here. Through its interaction with the nocturnal jet, the first arrival is often anomalously fast. Accompanying the increased propagation speed is a marked decrease in amplitude. It will be shown that an explanation for this behavior is given by geometrical acoustics.

Propagation of impulsive sound in the nocturnal boundary layer.

On clear, dry nights a sound channel, the nocturnal duct, forms in the lowest few hundred meters of the atmosphere. Impulsive sound propagating in a nocturnal duct undergoes severe distortion due to multipath effects and dispersion. At long ranges from the source, the signal from a single impulse is received as an extended wave train beginning with a series of distinct arrivals and ending with a low frequency tail. The nature and form of each of the arrivals will be described. The influence of elevated wind jets and the associated convergence zones will be discussed. Possible applications to signature identification and source ranging will be presented.

Predictions for the influence of the nocturnal jet on the long range propagation of impulsive signals

On clear nights, inland over flat ground, one generally finds a temperature inversion in the first hundred meters or so of the atmosphere. Near the ground, winds tend to be light, increasing with altitude. Above the temperature inversion one finds a stiff geostrophic wind known as the nocturnal jet. Theoretical predictions, based on ray theory and expansions in vertical modes, for the effect of the nocturnal jet on the long range propagation of impulsive signals are presented. For sufficiently short ranges, less than 3 km or so, the nocturnal jet has no effect. At these ranges only the temperature inversion and the light winds in the inversion play a role. At longer ranges the nocturnal jet significantly alters the arrival structure of the propagated signal. It is predicted that, due to coincident arrivals from the inversion and from the nocturnal jet, there is a segment of ranges about 1 km long, beginning at about 4 km, in which the amplitude of the first arrival becomes anomalously large and then splits into two distinct arrivals.

A High-Frequency Secondary Event During the 2004 Parkfield Earthquake

By using seismic records of the 2004 magnitude 6.0 Parkfield earthquake, we identified a burst of high-frequency seismic radiation that occurred about 13 kilometers northwest of the hypocenter and 5 seconds after rupture initiation. We imaged this event in three dimensions by using a waveform back-projection method, as well as by timing distinct arrivals visible on many of the seismograms. The high-frequency event is located near the south edge of a large slip patch seen in most seismic and geodetic inversions, indicating that slip may have grown abruptly at this point. The time history obtained from full-waveform back projection suggests a rupture velocity of 2.5 kilometers per second. Energy estimates for the subevent, together with long-period slip inversions, indicate a lower average stress drop for the northern part of the Parkfield earthquake compared with that for the region near its hypocenter, which is in agreement with stress-drop estimates obtained from small-magnitude aftershocks.

Anomalous Acoustic Signals Recorded by the CERI Seismic Network

Previous studies have shown a variety of atmospheric disturbances ( e.g. , sonic booms, meteoroid falls, thunder, and explosions) can be detected by a seismograph if the acoustic pressure wave energy is sufficiently strong. Kanamori et al . (1991) and Cates and Sturtevant (2002) used the seismic network in southern California to study sonic booms generated by the space shuttle and aircraft. Ishihara et al . (2003) used seismic data from a dense seismographic array in the northeastern region of Honshu Island, Japan, to determine the trajectory of a meteoroid. Kappus and Vernon (1991) analyzed the acoustic signature of thunder from a seismic instrument located at Kislovodsk, USSR. Atmospheric shock waves generated by sonic booms, meteoroid falls, and explosions have been observed in the Center for Earthquake Research and Information (CERI) Cooperative Seismic Network (Johnston 1987; Langston 2004). On 28 January 2004 at 01:58 UTC, 11 short-period and nine broadband CERI network stations (figure 1) recorded high signal-to-noise ratio signals generated by an unknown source (figure 2). A preliminary analysis of the waveforms and slow velocity across the network suggested that these signals were not generated by an earthquake but by an acoustic source. CERI also received several calls from the public in southern Missouri reporting large booming noises around the time when the event was recorded by the CERI network (G. Patterson, personal communication, 2005). One of these reports was from a medical worker in a two-story building in Poplar Bluff, Missouri. She reported that everyone on the second floor felt a hard jarring shake and heard a loud explosion, but few felt it on the first floor. The seismic signals have durations of 30 to 70 s with distinct later arrivals. For example, see stations PARM and WADM shown on figure 2. Figure 1. Location map showing the 20 …

Individual longitudinal Pochhammer-Chree modes in observed experimental signals

Plane waves and the Pochhammer-Chree solutions are both used to describe longitudinal axially symmetric wave propagation in solid cylinders. For interpreting experiments, plane waves provide a physical explanation for signals with multiple distinct arrivals. For signals without distinct arrivals the Pochhammer-Chree solutions are often used for interpretation, but the complexity of the solutions makes accurate interpretations difficult. This paper discusses some previous misinterpretations and shows how the Pochhammer-Chree solutions relate to signals with and without distinct arrivals by considering more than just the dispersion curves from the solutions.