scholarly journals Resolving the location of small intracontinental earthquakes using Open Access seismic and geodetic data: lessons from the 18 January 2017 mb 4.3, Niger, earthquake

2022 ◽  
Author(s):  
Timothy Craig ◽  
Steven Gibbons
Keyword(s):  
Open Access ◽  
Seismic Station ◽  
Body Wave ◽  
Time Frame ◽  
Geodetic Data ◽  
Arrival Times ◽  
Rupture Length ◽  
Seismological Data ◽  
Seismic Location ◽  
Test Ban

A low-magnitude earthquake was recorded on January 18, 2017, in the T\'{e}n\'{e}r\'{e} desert in Niger. This intraplate region is exceptionally sparsely covered with seismic stations and the closest open seismic station, G.TAM in Algeria at a distance of approximately 600 km, was unusually and unfortunately not operational at the time of the event. Body-wave magnitude estimates range from $m_b 4.2$ to $m_b 4.6$ and both seismic location and magnitude constraints are dominated by stations at teleseismic distances. The seismic constraints are strengthened considerably by array stations of the International Monitoring System for verifying compliance with the Comprehensive Nuclear Test-Ban-Treaty. This event, with magnitude relevant to low-yield nuclear tests, provides a valuable validation of the detection and location procedure for small land-based seismic disturbances at significant distances. For seismologists not in the CTBT system, the event is problematic as data from many of the key stations are not openly available. We examine the uncertainty in published routinely-determined epicenters by performing multiple Bayesloc location estimates with published arrival times considering both all published arrival times and those from open stations only. This location exercise confirms lateral uncertainties in seismologically-derived location no smaller than 10 km. Coherence for InSAR in this region is exceptionally high, and allows us to confidently detect a displacement of the order 6 mm in the time-frame containing the earthquake, consistent with the seismic location estimates, and with a lateral length scale consistent with an earthquake of this size, allowing location constraint to within one rupture length ($\leq 5$ km) -- significantly reducing the lateral uncertainty compared with relying on seismological data only. Combining Open Access-only seismological and geodetic data, we precisely constrain the source location, and conclude that this earthquake likely had a shallow source. We then discuss potential ways to continue the integration of geodetic data in the calibration of seismological earthquake location.

Velocity changes across the Ganos segment of the North Anatolian Fault Zone in NW Turkey from systematic variations in body wave arrival times

2021 ◽  
Author(s):  
Esref Yalcinkaya ◽  
Marco Bohnhoff ◽  
Patricia Martinez-Garzon ◽  
Ethem Görgün ◽  
Ali Pınar ◽  
...  
Keyword(s):  
Body Wave ◽  
Waveform Analysis ◽  
Marmara Region ◽  
Rupture Directivity ◽  
Data Set ◽  
High Resolution Data ◽  
Arrival Times ◽  
The North ◽  
Nw Turkey ◽  
Geological Units

<p>Imaging and characterizing transform fault sections that are capable to produce large earthquakes is crucial for evaluating seismic hazard and subsequent risk for nearby population centers. The Marmara Fault near the megacity of Istanbul is one of the best defined seismic gaps in the world and its complexity is captured by seismological, geodetic and geological data. A local dense seismic array (MONGAN) provides a high resolution data set allowing to image the Ganos fault separating two different geological units in the western Marmara region. First results of the waveform analysis from this array present systematic early-phase arrivals at the seismic stations located on the northern block of the Ganos fault which comprises geological units including older and more compact materials than that of the southern block. This difference in the arrival times causes the earthquake epicenters to shift further north than the real locations. In this preliminary results, the early-arrivals will be evaluated according to source azimuths and distances, and possible earth models and wave paths will be discussed. The results have implications for rupture directivity during future earthquakes as input for hazard and risk models for the Marmara region.</p>

scholarly journals Monitoring long-term changes of glacial seismic activity with continuous seismological observations: a case study from Spitsbergen

2016 ◽  
Author(s):  
W. Gajek ◽  
J. Trojanowski ◽  
M. Malinowski
Keyword(s):  
Seismic Activity ◽  
Seismic Station ◽  
Flow Analysis ◽  
Seismic Signal ◽  
Signal Frequency ◽  
Steady Increase ◽  
Fuzzy Logic Algorithm ◽  
Temperature And Precipitation ◽  
Seismological Data

Abstract. Changes in the global temperature balance have proved to have a major impact on the cryosphere and therefore retreating glaciers are the symbol of the warming climate. Long-term measurements of geophysical parameters provide the insight into the dynamics of those processes over many years. Here we explore the possibility of using data recorded by permanent seismological stations to monitor glacial seismic activity. Our study focuses on year-to-year changes in seismicity of the Hansbreen glacier (southern Spitsbergen). We have processed 7-year-long continuous seismological data recorded by a broadband station located in the fjord of Hornsund, obtaining seismicity distribution between 2008 and 2014. To distinguish between glacier- and non-glacier-origin events with the data from only one seismic station in the area, we developed a new fuzzy logic algorithm based on the seismic signal frequency and the energy flow analysis. Our research has revealed that the number of detected glacier-origin events over the last two years has doubled. We also observed that the annual events distribution correlates well with the temperature and precipitation data. In order to further support our observations, we have analysed 5-year-long seismological data recorded by a broadband station located in Ny-Ålesund (western Spitsbergen). Distribution of glacier-origin tremors detected in the vicinity of the Kronebreen glacier shows a steady increase from year to year, however not as significant as for the Hornsund dataset.

Abstract P257: Getting to the Golden Hour: Correlating “Door-To” Times with 60-Minute Administration of tPA in an Academic Medical Center

2011 ◽  
Vol 4 (suppl_2) ◽  
Author(s):  
Ann M Leonhardt ◽  
Curtis G Benesch ◽  
Kate C Young
Keyword(s):  
Medical Center ◽  
Academic Medical Center ◽  
Rank Correlation ◽  
Correlation Coefficients ◽  
Time Frame ◽  
Arrival Times ◽  
Golden Hour ◽  
Stroke Team ◽  
Time Standards ◽  
Scheduling Protocols

Introduction: The efficacy of intravenous tPA for the treatment of acute stroke diminishes over time. The AHA/ASA and NINDS recommend a goal door to needle time of 60 minutes or less. Objective: Identify potential barriers to tPA administration within 60 minutes of arrival. Methods: Retrospective review of tPA adsinistration using “Get With the Guidelines” (GWTG) and institutional records from January 1, 2009 through December 31, 2010 (n=100). Spearman rank correlation coefficients were calculated for the NINDS recommended time standards, age and NIH Stroke Scale (NIHSS) score. We used a receiver-operator curve (ROC) to identify the door to CT time predictive of tPA administration ≤ 60 minutes. Results: Median door to physician, door to CT, and door to stroke team times were within the recommended goals. Door to CT (ρ=0.53, p<0.0001), and door to stroke team (ρ=0.33, p<0.01) times were positively correlated with door to tPA times. Last known well to arrival (ρ= -0.28, p<0.01) and NIHSS (ρ= -0.32, p<0.01) were negatively correlated with door to tPA times; patients with higher NIHSS and longer last-known-well to arrival times received tPA in a shorter time frame. Age and door to physician time were not correlated with tPA treatment times. After adjusting for the other benchmarks and NIHSS, only door to CT remained significantly correlated with door to IV tPA (partial correlation coefficient=0.40, p<0.001). The ROC curve showed that a goal time of 20 minutes or less for door to CT initiation had the best sensitivity and specificity for predicting tPA administration within 60 minutes. Conclusion: In keeping with the recommended time goals, median times for the intermediate steps were within target. Our median tPA times, however, did not meet the 60 minute goal. Door to CT initiation was the variable that most strongly correlated with door to needle times. Process issues such as order entry and scheduling protocols may be barriers to obtaining CT within the 20 minute time frame identified by our analysis. Other barriers after the CT scan is obtained must be identified to facilitate faster tPA administration. Further evaluation of these factors is warranted to better ensure the timely delivery of tPA to stroke patients, thereby improving patient outcomes.

Seismic Rays

2017 ◽  
Author(s):  
John A. Adam
Keyword(s):  
Inverse Problem ◽  
Seismic Tomography ◽  
Seismic Waves ◽  
Seismic Station ◽  
Three Dimensional ◽  
Arrival Times ◽  
The Earth ◽  
Straight Lines ◽  
Ray Path ◽  
Uniform Composition

This chapter focuses on the underlying mathematics of seismic rays. Seismic waves caused by earthquakes and explosions are used in seismic tomography to create computer-generated, three-dimensional images of Earth's interior. If the Earth had a uniform composition and density, seismic rays would travel in straight lines. However, it is broadly layered, causing seismic rays to be refracted and reflected across boundaries. In order to calculate the speed along the wave's ray path, the time it takes for a seismic wave to arrive at a seismic station from an earthquake needs to be determined. Arrival times of different seismic waves allow scientists to define slower or faster regions deep in the Earth. The chapter first presents the relevant equations for seismic rays before discussing how rays are propagated in a spherical Earth. The Wiechert-Herglotz inverse problem is considered, along with the properties of X in a horizontally stratified Earth.

scholarly journals Unexpected Shallow Earthquake of August 1st, 2020 in the North of Indramayu, West Java, Indonesia

2021 ◽  
Vol 873 (1) ◽  
pp. 012043
Author(s):  
Jaya Murjaya ◽  
Pepen Supendi ◽  
Dwikorita Karnawati ◽  
Subagyo Pramumijoyo
Keyword(s):  
Seismic Station ◽  
Moment Tensor ◽  
Focal Mechanism Solution ◽  
West Java ◽  
Waveform Data ◽  
Arrival Times ◽  
S Waves ◽  
The North ◽  
Focus Depth ◽  
Deep Focus

Abstract During the last one hundred years, there are no shallow seismicity in the north of Java. This area is dominated by intermediate and deep focus earthquakes due to the subducted Indo-Australian slab. An earthquake with magnitude ML 4.5 struck Indramayu, north of West Java on August 1, 2020. According to the Agency for Meteorology, Climatology, and Geophysics (BMKG), the earthquake was felt III MMI scale in Indramayu and its vicinity. We used waveform data from BMKG seismic station in West Java, then we picked P-and S-waves arrival times from each station and hypocenter location was determined by Geiger method. We have detected Pn before Pg phase on four BMKG seismic stations, indicating a shallow crustal earthquake. Our inversion show that the earthquake occurred in 6.1805° S, 108.2612° E with 5 km focus depth at 16:24:38 GMT+7. Our focal mechanism solution was determined by using moment tensor inversion shows a strike-slip faulting, which corresponds to the active fault in the north of Indramayu.

Predicting Near-Term Train Schedule Performance and Delay Using Bi-Level Random Forests

2019 ◽  
Vol 2673 (5) ◽  
pp. 564-573 ◽  
Author(s):  
Mohammad Amin Nabian ◽  
Negin Alemazkoor ◽  
Hadi Meidani
Keyword(s):  
Time Frame ◽  
Learning Approaches ◽  
Arrival Times ◽  
Primary Level ◽  
Passenger Train ◽  
Proposed Model ◽  
Level Model ◽  
Schedule Performance ◽  
Near Term ◽  
Delay Prediction

Accurate near-term passenger train delay prediction is critical for optimal railway management and providing passengers with accurate train arrival times. In this work, a novel bi-level random forest approach is proposed to predict passenger train delays in the Netherlands. The primary level predicts whether a train delay will increase, decrease, or remain unchanged in a specified time frame. The secondary level then estimates the actual delay (in minutes), given the predicted delay category at primary level. For validation purposes, the proposed model has been compared with several alternative statistical and machine-learning approaches. The results show that the proposed model provides the best prediction accuracy compared with other alternatives. Moreover, constructing the proposed bi-level model is computationally cheap, thereby being easily applicable.

scholarly journals The New Seismotectonic Atlas of Greece (v1.0) and Its Implementation

Geosciences ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 447
Author(s):  
Ioannis Kassaras ◽  
Vasilis Kapetanidis ◽  
Athanassios Ganas ◽  
Andreas Tzanis ◽  
Chrysanthi Kosma ◽  
...  
Keyword(s):  
Data Processing ◽  
Risk Mitigation ◽  
Active Tectonics ◽  
Geological Mapping ◽  
Geodetic Data ◽  
Joint Analysis ◽  
Seismological Data ◽  
Geodynamic Processes ◽  
Gis Environment ◽  
Of Greece

Knowledge and visualization of the present-day relationship between earthquakes, active tectonics and crustal deformation is a key to understanding geodynamic processes, and is also essential for risk mitigation and the management of geo-reservoirs for energy and waste. The study of the complexity of the Greek tectonics has been the subject of intense efforts of our working group, employing multidisciplinary methodologies that include detailed geological mapping, geophysical and seismological data processing using innovative methods and geodetic data processing, involved in surveying at various scales. The data and results from these studies are merged with existing or updated datasets to compose the new Seismotectonic Atlas of Greece. The main objective of the Atlas is to harmonize and integrate the most recent seismological, geological, tectonic, geophysical and geodetic data in an interactive, online GIS environment. To demonstrate the wealth of information available in the end product, herein, we present thematic layers of important seismotectonic and geophysical content, which facilitates the comprehensive visualization and first order insight into seismic and other risks of the Greek territories. The future prospect of the Atlas is the incorporation of tools and algorithms for joint analysis and appraisal of these datasets, so as to enable rapid seismotectonic analysis and scenario-based seismic risk assessment.

Potential effect of seasonally varying station thresholds on joint-maximum-likelihood magnitude estimates from bulletin data 

2021 ◽  
Author(s):  
Sheila Peacock
Keyword(s):  
Maximum Likelihood ◽  
Body Wave ◽  
Monitoring Network ◽  
Test Site ◽  
Potential Effect ◽  
Likelihood Method ◽  
Different Seasons ◽  
Noise Threshold ◽  
Test Ban ◽  
Magnitude Estimates

&lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;p&gt;Accurate seismic body-wave magnitudes (m&lt;sub&gt;b&lt;/sub&gt;) are important in nuclear test-ban treaty verification.&amp;#160; Network mean magnitudes are known to be biased when the effect of noise obscuring signal at some stations in the monitoring network is ignored.&amp;#160; To overcome this bias a joint-maximum-likelihood method is used to invert bulletin amplitude and period measurements at a network of stations from a number of closely spaced sources, to estimate unbiased network m&lt;sub&gt;b&lt;/sub&gt; values and station corrections. For each station a noise threshold is determined independently using the Kelly &amp; Lacoss (1969) method, assuming that large samples of amplitudes reported in a bulletin (in this case from the International Seismological Centre, ISC) follow a Gutenberg-Richter distribution. Where stations report arrivals sufficiently frequently, the noise threshold can be estimated separately for different seasons, to highlight variations caused by, for instance, storms or freezing of nearby ocean.&amp;#160; The noise thresholds at some stations differ by up to 0.4 magnitude units between seasons.&amp;#160; Sensitivity of maximum-likelihood magnitude estimates of a group of announced explosions at the Nevada Test Site to variations in threshold at Canadian Arctic stations (compared with using the annual mean) is generally small (&lt;&amp;#8764;0.01-0.02 units), and greatest for low-magnitude events in the &amp;#8220;noisy&amp;#8221; season, when the station magnitudes are below the seasonal threshold but above the annual average threshold.&lt;/p&gt; &lt;p&gt;UK Ministry of Defence &amp;#169; Crown copyright 2021/AWE&lt;/p&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt;

The collection of seismic station readings

1966 ◽  
Vol 290 (1422) ◽  
pp. 461-471
Keyword(s):  
Reference Point ◽  
Arrival Time ◽  
Seismic Station ◽  
Reference Points ◽  
Origin Time ◽  
Arrival Times ◽  
Starting Point ◽  
Recording Station ◽  
Set Up ◽  
International Seismological Centre

The chief problem of the International Seismological Centre in Edinburgh is to determine focal parameters of seismic events from a stream of station reports. These station reports are identifiable only by the arrival time of the seismic impulse at the given station, as the source location and tim e are not, in general, known when the readings are made. As several events may sometimes occur within a few minutes of each other, and as the P waves from each event may take up to 20 min to reach the points of detection, considerable overlapping is to be expected. One proposal, which will be discussed, is to set up a pattern of reference points covering the Earth, and to subtract the travel time between each reference point and the recording station from the arrival time given in the station report. Each subtraction yields an estimate of what the origin time would have been if the source had been located close to the reference point. If a source actually is close to one of the reference points, the apparent source times form a much sharper ‘bunch’ in a time series than do the arrival times from which they were derived. In addition to assisting recognition, the process yields a provisional epicentre and a set of first residuals and, as such, provides a favourable starting point for the following computations.

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