Appraising relative earthquake location errors

1992 ◽  
Vol 82 (2) ◽  
pp. 836-859 ◽  
Author(s):  
Gary L. Pavlis
Keyword(s):  
Travel Time ◽  
Upper Bound ◽  
Large Scale ◽  
Velocity Structure ◽  
Order Approximation ◽  
Earthquake Location ◽  
Travel Times ◽  
Spatial Error ◽  
Location Errors ◽  
Error Terms

Abstract Earthquake location estimates suffer from two types of errors: (1) systematic offsets caused by large scale earth structure, and (2) scatter of locations of different earthquakes relative to each other. I show that relative location errors are controlled by four separate error terms: (1) scatter caused by random, measurement error; (2) nonlinear effects; (3) mislocations caused by interaction of errors in modeling travel times with variations in the number and quality of arrivals recorded by different events; and (4) mislocations caused by variations in how errors in modeling travel times vary with position inside the real Earth. The first can be handled by conventional statistical methods. The second can be bounded using a second-order approximation, provided one can provide a reasonable estimate for an upper bound on the total spatial error that might be present in the location estimate. I demonstrate that the size of each of the two error terms related to inadequate knowledge of the Earth's velocity structure can be bounded provided we can determine an upper bound on travel-time errors as a function of distance. I describe an empirical approach for determining such a bound using differences between the sum of squared residuals of earthquakes located with all available data and the same event located with a single arrival deleted. This calculation is repeated for all arrivals and used to construct an upper bound on travel-time errors as a function of distance. The concepts developed are applied to bound errors in locations of earthquakes in the Garm region of central Asia, and they demonstrate the utility of these ideas in sorting out events with minimal relative error.

Strategic Evacuation for Hurricanes and Regional Events with and without Autonomous Vehicles

2021 ◽  
pp. 036119812110074
Author(s):  
Jooyong Lee ◽  
Kara M. Kockelman
Keyword(s):  
Travel Time ◽  
Large Scale ◽  
Scheduling Algorithm ◽  
Autonomous Vehicle ◽  
Time Span ◽  
Network Congestion ◽  
Travel Times ◽  
Total Delay ◽  
Evacuation Time ◽  
Conflicting Objectives

A scheduling algorithm is developed for optimal planning of large-scale, complex evacuations to minimize total delay plus travel time across residents. The algorithm is applied to the eight-county Houston-Galveston region and land use setting under the 2017 Hurricane Harvey scenario with multiple destinations. Autonomous vehicle (AV) use under central guidance is also tested, to demonstrate the evacuation time benefits of AVs. Higher share of AVs delivers more efficient evacuation performance, thanks to greater reliability on evacuation order compliance, lower headways, and higher road capacity. Furthermore, 100% AV use delivers lower overall evacuation costs and network clearance times and less uncertainty in travel times (via lower standard deviation in). Based on evaluations of different evacuation schedules, a 50% compressed evacuation time span resulted in longer travel times and network congestion. A 50% longer evacuation time span reduced residents' total travel time and network congestion, but increased the evacuation cost. As expected, evacuation efficiency falls when evacuees do not comply with evaucation schedules. Large shares of AVs will not be possible in the near future, so methods to enhance evacuees' compliance behavior (e.g., enforced and prioritized evacuation orders) should be considered until a meaningful level of AV technical maturity and penetration rate is available. This paper demonstrates the benefits of scheduled departure times, AV use, and evacuation order compliance, which help balance conflicting objectives during emergencies.

Constructing P-velocity models to fit restricted sets of travel-time data

1969 ◽  
Vol 59 (3) ◽  
pp. 1407-1414
Author(s):  
George Backus ◽  
Freeman Gilbert
Keyword(s):  
Travel Time ◽  
Standard Error ◽  
Experimental Error ◽  
Velocity Structure ◽  
Travel Times ◽  
Time Data ◽  
Velocity Models ◽  
Travel Time Data ◽  
Earth Models ◽  
Finite Set

abstract A scheme recently proposed by the authors for constructing Earth models which fit a given finite set of gross Earth data is applied to the problem of constructing a P-velocity structure which, within experimental error, fits the observed travel times in the range Δ = 25°(5°)95°. Three such models are obtained, all of which fit the observed travel times with residuals less than 0.06s, whereas 0.5s is the estimated standard error of the observations. The models differ mainly in the outer 700 km of the mantle.

scholarly journals Teleseismic P-residual study in the Italian region - inferences on large scale anisotropic structure of the subcrustal lithosphere

1998 ◽  
Vol 41 (1) ◽  
Author(s):  
J. Plomerová ◽  
V. Babuska ◽  
R. Scarpa
Keyword(s):  
Travel Time ◽  
Upper Mantle ◽  
Large Scale ◽  
Velocity Structure ◽  
P Wave ◽  
Anisotropic Structure ◽  
Low Velocity ◽  
Arrival Times ◽  
Station Corrections ◽  
Lateral Variations

Jeffreys-Bullen (absolute) and relative P-wave travel-time residuals were analyzed over Italy and its surrounding using P arrival times from the ISC bulletins supplemented by the data from local observatories. We analyzed the travel-time station corrections by two independent methods to obtain information on lateral variations of the velocity structure over the area and a view of possible upper mantle anisotropy. In the first method, the station corrections are computed as a constant and two cosine terms with appropriate phase shifts. Besides a static term, the second method allows us to study the relative residuals in dependence both on azimuths and incidence angles and thus to investigate their spatial variations and to map lateral variations of anisotropic structure of the subcrustal lithosphere. The high and low-velocity directions inferred from the spatial distribution of the relative residuals as well as the high- and low-velocity upper mantle heterogeneities reflect the geodynamic development of the region, governed by the collision between the African and Eurasian plates

Evaluation Results of the Amsterdam, Netherlands, Practical Trial with In-Car Travel and Route Advice

2017 ◽  
Vol 2621 (1) ◽  
pp. 38-45 ◽  
Author(s):  
Isabel Wilmink ◽  
Eline Jonkers ◽  
Maaike Snelder ◽  
Gerdien Klunder
Keyword(s):  
Travel Time ◽  
Traffic Flow ◽  
Large Scale ◽  
User Behavior ◽  
Route Guidance ◽  
Travel Times ◽  
Guidance Services ◽  
Social Navigation ◽  
Total Travel Time ◽  
Message Signs

Travel and route guidance services are widely available. Social navigation services that provide travelers with advice aimed at minimizing driver travel time, while also taking into account the effect on travel times of other travelers, are relatively new. Theoretically, social navigation has been shown to reduce total travel time by 10% to 30%. This paper presents the evaluation results of a large-scale field trial for pretrip and on-trip route advice with load balancing, in which about 20,000 participants were active. The evaluation provided insight into the potential effects of in-car information services, such as effects on user behavior, traffic flow effects, and technical aspects. Participants used mostly the pretrip advisories. Compliance with the on-trip route advice was 50%, which was considered high (compared with compliance with route advice on variable message signs). An effect on traffic flow could not be measured, as penetration rates were (despite thousands of users) still too low. An offline study using measured travel times combined with a traffic model, however, showed that substantial delay reductions can be achieved for the Amsterdam, Netherlands, region. Participants’ appreciation of the service resulted in a mixed picture with positive and negative ratings. The main practical contribution of this paper is that the results can be used to develop social navigation services. Empirical insights about route advice compliance can be seen as the main scientific contribution.

scholarly journals “In cities, it’s not far, but it takes long”: comparing estimated and replicated travel times to reach life-saving obstetric care in Lagos, Nigeria

2021 ◽  
Vol 6 (1) ◽  
pp. e004318
Author(s):  
Aduragbemi Banke-Thomas ◽  
Kerry L M Wong ◽  
Francis Ifeanyi Ayomoh ◽  
Rokibat Olabisi Giwa-Ayedun ◽  
Lenka Benova
Keyword(s):  
Travel Time ◽  
Friction Surface ◽  
Obstetric Care ◽  
Travel Times ◽  
Night Time ◽  
Google Maps ◽  
Surface Approach ◽  
Low Resource ◽  
Life Saving ◽  
The Cost

BackgroundTravel time to comprehensive emergency obstetric care (CEmOC) facilities in low-resource settings is commonly estimated using modelling approaches. Our objective was to derive and compare estimates of travel time to reach CEmOC in an African megacity using models and web-based platforms against actual replication of travel.MethodsWe extracted data from patient files of all 732 pregnant women who presented in emergency in the four publicly owned tertiary CEmOC facilities in Lagos, Nigeria, between August 2018 and August 2019. For a systematically selected subsample of 385, we estimated travel time from their homes to the facility using the cost-friction surface approach, Open Source Routing Machine (OSRM) and Google Maps, and compared them to travel time by two independent drivers replicating women’s journeys. We estimated the percentage of women who reached the facilities within 60 and 120 min.ResultsThe median travel time for 385 women from the cost-friction surface approach, OSRM and Google Maps was 5, 11 and 40 min, respectively. The median actual drive time was 50–52 min. The mean errors were >45 min for the cost-friction surface approach and OSRM, and 14 min for Google Maps. The smallest differences between replicated and estimated travel times were seen for night-time journeys at weekends; largest errors were found for night-time journeys at weekdays and journeys above 120 min. Modelled estimates indicated that all participants were within 60 min of the destination CEmOC facility, yet journey replication showed that only 57% were, and 92% were within 120 min.ConclusionsExisting modelling methods underestimate actual travel time in low-resource megacities. Significant gaps in geographical access to life-saving health services like CEmOC must be urgently addressed, including in urban areas. Leveraging tools that generate ‘closer-to-reality’ estimates will be vital for service planning if universal health coverage targets are to be realised by 2030.

Estimation of Path Travel Time Distributions in Stochastic Time-Varying Networks with Correlations

2021 ◽  
pp. 036119812110184
Author(s):  
Monika Filipovska ◽  
Hani S. Mahmassani ◽  
Archak Mittal
Keyword(s):  
Time Dependence ◽  
Travel Time ◽  
Correlation Structure ◽  
Time Varying ◽  
Travel Times ◽  
Trajectory Data ◽  
Time Varying Networks ◽  
Transportation Research ◽  
Search Approach ◽  
Stochastic Time

Transportation research has increasingly focused on the modeling of travel time uncertainty in transportation networks. From a user’s perspective, the performance of the network is experienced at the level of a path, and, as such, knowledge of variability of travel times along paths contemplated by the user is necessary. This paper focuses on developing approaches for the estimation of path travel time distributions in stochastic time-varying networks so as to capture generalized correlations between link travel times. Specifically, the goal is to develop methods to estimate path travel time distributions for any path in the networks by synthesizing available trajectory data from various portions of the path, and this paper addresses that problem in a two-fold manner. Firstly, a Monte Carlo simulation (MCS)-based approach is presented for the convolution of time-varying random variables with general correlation structures and distribution shapes. Secondly, a combinatorial data-mining approach is developed, which aims to utilize sparse trajectory data for the estimation of path travel time distributions by implicitly capturing the complex correlation structure in the network travel times. Numerical results indicate that the MCS approach allowing for time-dependence and a time-varying correlation structure outperforms other approaches, and that its performance is robust with respect to different path travel time distributions. Additionally, using the path segmentations from the segment search approach with a MCS approach with time-dependence also produces accurate and robust estimates of the path travel time distributions with the added benefit of shorter computation times.

scholarly journals Equity Effects of Congestion Charges: An Exploratory Analysis with MATSim

2017 ◽  
Vol 2670 (1) ◽  
pp. 75-82 ◽  
Author(s):  
Lucas Meyer de Freitas ◽  
Oliver Schuemperlin ◽  
Milos Balac ◽  
Francesco Ciari
Keyword(s):  
Travel Time ◽  
Large Scale ◽  
Agent Based ◽  
Promising Tool ◽  
Travel Time Savings ◽  
Time Savings ◽  
Time Changes ◽  
High Level ◽  
Congestion Charging ◽  
Equity Effects

This paper shows an application of the multiagent, activity-based transport simulation MATSim to evaluate equity effects of a congestion charging scheme. A cordon pricing scheme was set up for a scenario of the city of Zurich, Switzerland, to conduct such an analysis. Equity is one of the most important barriers toward the implementation of a congestion charging system. After the challenges posed by equity evaluations are examined, it is shown that agent-based simulations with heterogeneous values of time allow for an increased level of detail in such evaluations. Such detail is achieved through a high level of disaggregation and with a 24-h simulation period. An important difference from traditional large-scale models is the low degree of correlation between travel time savings and welfare change. While traditional equity analysis is based on travel time savings, MATSim shows that choice dimensions not included in traditional models, such as departure time changes, can also play an important role in equity effects. The analysis of the results in light of evidence from the literature shows that agent-based models are a promising tool to conduct more complete equity evaluations not only of congestion charges but also of transport policies in general.

scholarly journals Dynamic Bus Travel Time Prediction Models on Road with Multiple Bus Routes

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Cong Bai ◽  
Zhong-Ren Peng ◽  
Qing-Chang Lu ◽  
Jian Sun
Keyword(s):  
Travel Time ◽  
Dynamic Model ◽  
Kalman Filtering ◽  
Prediction Models ◽  
Support Vector ◽  
Travel Times ◽  
Travel Time Prediction ◽  
Real World Data ◽  
Time Prediction ◽  
Bus Travel Time

Accurate and real-time travel time information for buses can help passengers better plan their trips and minimize waiting times. A dynamic travel time prediction model for buses addressing the cases on road with multiple bus routes is proposed in this paper, based on support vector machines (SVMs) and Kalman filtering-based algorithm. In the proposed model, the well-trained SVM model predicts the baseline bus travel times from the historical bus trip data; the Kalman filtering-based dynamic algorithm can adjust bus travel times with the latest bus operation information and the estimated baseline travel times. The performance of the proposed dynamic model is validated with the real-world data on road with multiple bus routes in Shenzhen, China. The results show that the proposed dynamic model is feasible and applicable for bus travel time prediction and has the best prediction performance among all the five models proposed in the study in terms of prediction accuracy on road with multiple bus routes.

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