Relative Time Corrections for Historical Analog Seismograms Using the Single-Day Ambient Noise Correlation Function

2020 ◽  
Vol 110 (6) ◽  
pp. 3185-3195
Author(s):  
Thomas Lee ◽  
Miaki Ishii ◽  
Paul Okubo
Keyword(s):  
Correlation Function ◽  
Noise Correlation ◽  
Relative Time ◽  
P Waves ◽  
Arrival Times ◽  
Volcano Observatory ◽  
Local Earthquake ◽  
Noise Correlation Function ◽  
Using Data ◽  
Time Accuracy

ABSTRACT This study examines analog seismograms that were generated when most seismic stations had their own clock for timing, making precise comparison of time between different stations difficult. Availability of accurate relative timing facilitates differential travel-time analyses, such as seismic tomography and local earthquake relocations, to be performed using data originally recorded on paper or other physical media. These analyses allow for the investigation of longer-term processes like the earthquake cycle or climate change. We take advantage of the continuous nature of seismic noise to determine the relative time correction between two stations by leveraging the symmetry of the noise correlation function. This procedure is applied to two Global Positioning System-timed stations in the Hawaiian Volcano Observatory network demonstrating subsecond time accuracy. The technique is then applied to analog records from comparable stations between 7 and 10 August in 1988, and relative time corrections of up to about 6 s are obtained. These corrections are confirmed by the relative arrival times of teleseismic P waves of earthquake doublets.

scholarly journals Observations and Analysis of Uncorrelated Rain

2005 ◽  
Vol 62 (11) ◽  
pp. 4071-4083 ◽  
Author(s):  
Michael L. Larsen ◽  
Alexander B. Kostinski ◽  
Ali Tokay
Keyword(s):  
Correlation Function ◽  
Pair Correlation ◽  
Two Dimensional ◽  
Statistical Tool ◽  
Arrival Times ◽  
Temporal Precision ◽  
Spatially Correlated ◽  
Radar Meteorology ◽  
Rain Events ◽  
Using Data

Abstract Most microphysical models in precipitation physics and radar meteorology assume (at least implicitly) that raindrops are completely uncorrelated in space and time. Yet, several recent studies have indicated that raindrop arrivals are often temporally and spatially correlated. Resolution of this conflict must begin with observations of perfectly uncorrelated rainfall, should such “perfectly steady rain” exist at all. Indeed, it does. Using data with high temporal precision from a two-dimensional video disdrometer and the pair-correlation function, a scale-localized statistical tool, several ∼10–20-min rain episodes have been uncovered where no clustering among droplet arrival times is found. This implies that (i) rain events exist where current microphysical models can be tested in an optimal manner and (ii) not all rain can be properly described using fractals.

scholarly journals Recovering and monitoring the thickness, density and elastic properties of sea ice from seismic noise recorded in Svalbard

2021 ◽  
Author(s):  
Agathe Serripierri ◽  
Ludovic Moreau ◽  
Pierre Boue ◽  
Jérôme Weiss ◽  
Philippe Roux
Keyword(s):  
Mechanical Properties ◽  
Correlation Function ◽  
Sea Ice ◽  
Elastic Properties ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Ice Thickness ◽  
Noise Correlation ◽  
Sea Ice Thickness ◽  
Noise Correlation Function

Abstract. Due to global warming, the decline in the Arctic sea ice has been accelerating over the last four decades, with a rate that was not anticipated by climate models. To improve these models, there is the need to rely on comprehensive field data. Seismic methods are known for their potential to estimate sea-ice thickness and mechanical properties with very good accuracy. However, with the hostile environment and logistical difficulties imposed by the polar regions, seismic studies have remained rare. Due to the rapid technological and methodological progress of the last decade, there has been a recent reconsideration of such approaches. This paper introduces a methodological approach for passive monitoring of both sea-ice thickness and mechanical properties. To demonstrate this concept, we use data from a seismic experiment where an array of 247 geophones was deployed on sea ice in a fjord at Svalbard, between March 1 and 24, 2019. From the continuous recording of the ambient seismic field, the empirical Green's function of the seismic waves guided in the ice layer was recovered via the so-called 'noise correlation function'. Using specific array processing, the multi-modal dispersion curves of the ice layer were calculated from the noise correlation function, and then inverted for the thickness and elastic properties of the sea ice via Bayesian inference. The evolution of sea-ice properties was monitored for 24 days, and values are consistent with the literature, as well as with measurements made directly in the field.

scholarly journals Computer Assisted Localization of a Heart Arrhythmia

2018 ◽  
Author(s):  
Chris Vogl ◽  
Peng Zheng ◽  
Stephen P. Seslar ◽  
Aleksandr Y. Aravkin
Keyword(s):  
Diagnostic Procedure ◽  
Feasibility Problem ◽  
Computer Assisted ◽  
Optimization Approach ◽  
Arrival Times ◽  
Heart Arrhythmia ◽  
Simulation Based ◽  
Heart Anatomy ◽  
Using Data ◽  
Diagnostic Catheter

AbstractWe consider the problem of locating a point-source heart arrhythmia using data from a standard diagnostic procedure, where a reference catheter is placed in the heart, and arrival times from a second diagnostic catheter are recorded as the diagnostic catheter moves around within the heart.We model this situation as a nonconvex feasibility problem, where given a set of arrival times, we look for a source location that is consistent with the available data. We develop a new optimization approach and fast algorithm to obtain online proposals for the next location to suggest to the operator as she collects data. We validate the procedure using a Monte Carlo simulation based on patients’ electrophysiological data. The proposed procedure robustly and quickly locates the source of arrhythmias without any prior knowledge of heart anatomy.

Seismic analysis of the 7 January 1998 Chemical plant explosion at Kean Canyon, Nevada

1999 ◽  
Vol 89 (4) ◽  
pp. 938-945 ◽  
Author(s):  
Gene A. Ichinose ◽  
Kenneth D. Smith ◽  
John G. Anderson
Keyword(s):  
Seismic Analysis ◽  
Correlation Method ◽  
Chemical Safety ◽  
P Waves ◽  
Arrival Times ◽  
Chemical Company ◽  
Optimal Separation ◽  
The Difference ◽  
Possible Cause

Abstract An accident at the Sierra Chemical Company Kean Canyon plant, 16 km east of Reno, Nevada, resulted in two explosions 3.52 sec apart that devastated the facility. An investigation into a possible cause for the accident required the determination of the chronological order of the explosions. We resolved the high-precision relative locations and chronology of the explosions using a cross-correlation method applied to both seismic and air waves. The difference in relative arrival times of air waves between the explosions indicated that the first explosion occurred at the northern site. We then determined two station centroid separations between explosions, which average about 73 m with uncertainties ranging from ± 17 to 41 m depending on the alignment of station pairs. We estimated a centroid separation of 80 m using P waves with a larger uncertainty of ± 340 m. We performed a grid search for an optimal separation and the azimuth by combining air-wave arrivals from three station pairs. The best solution for the relative location of the second explosion is 73.2 m S35°E from the first explosion. This estimate is well within the uncertainties of the survey by the U.S. Chemical Safety and Hazard Investigation Board (CSB). The CSB reported a separation of approximately 76.2 m S33°E. The spectral amplitudes of P waves are 3 to 4 times higher for the second explosion relative to the first explosion, but the air waves have similar spectral amplitudes. We suggest that this difference is due to the partitioning of energy between the ground and air caused by downward directivity at the southern explosion, and upward directivity at the northern explosion. This is consistent with the absence of a crater for the first explosion and a 1.8-m-deep crater for the second explosion.

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