Velocity-density Relation Research Articles

Sound velocities and thermal equation of state of fcc-iron-nickel alloys at high pressure and high temperature: Implications for the cores of Moon and several planets

Fcc-Fe-Ni alloy is believed to be the most dominant solid constitute of moderate-sized terrestrial planetary cores. Investigating the physical properties, especially the density and sound velocity of Fe-Ni alloys and comparing them with seismic observations is an indispensable approach to constructing compositional models for planetary interiors. In this study, we conducted sound velocity measurements on Fe-Ni alloys with 10 wt.% and 20 wt.% Ni up to ∼13.5 GPa and 1073 K, using the ultrasonic interferometry technique in a multi-anvil apparatus in conjunction with synchrotron radiation. By fitting the experimental data to finite strain equations, the bulk and shear moduli and their pressure and temperature derivatives are derived, yielding KS0 =145.8(14) GPa, G0 = 73.2(7) GPa, KS0’ = 5.89(24), G0’ = 2.89(8), (∂KS/∂T)P = -0.0181(12) GPa/K and (∂G/∂T)P = -0.0393(10) GPa/K for fcc-Fe80Ni20. An examination of the density-velocity relationship shows that compressional wave velocity is insensitive to temperature within the current pressure and temperature range, while shear wave velocity exhibits a large reduction with increasing temperature. Extrapolation of the sound velocities following the finite strain theories suggests that much slower Vs should be expected at pressure and temperature conditions corresponding to those of the lunar core. Possible core density and velocity profiles for other moderate planets and satellites, such as Mars, Mercury, and Ganymede are also calculated.

Modeling and Simulation of Vehicle Velocity-Density on Buah Batu Road Using Decision Tree Regression

This study aims to explore and simulate the traffic flow model on Buah Batu Road using the velocity-density function generated by the Decision Tree Regression method. The model utilizes a macroscopic approach, specifically the Lightill, Whitham, and Richards (LWR) model, which considers vehicle interactions. Observational data were collected directly from Buah Batu Road and processed to produce a velocity-density function, which shows that vehicle speed decreases as density increases, following a non-linear but step-like pattern. The velocity function generated by the Decision Tree Regression indicates that for low density (ρ < 0.102), the average speed is predicted to be around 3.681 to 4.551, while at high density (ρ > 0.273), the speed drops to around 1.411 or lower. The simulation was conducted on a 60-meter road segment with a total simulation time of 5 minutes and a grid resolution of 300 points. At the beginning of the simulation, a peak density of 0.70 was recorded in the 15-25 meter segment, which then shifted and decreased to 0.50 in the 30-50 meter segment by the end. The results indicate that vehicle movement reduces density and improves traffic flow. Thus, the Decision Tree Regression method has proven effective in modelling and simulating the velocity-density relationship to understand traffic dynamics on Buah Batu Road.

Three-dimensional joint inversion of surface wave dispersion and gravity data using a petrophysical approach: an application to Los Humeros Geothermal Field

SUMMARY We present a method to jointly invert surface wave dispersion data and gravity measurements for 3-D shear wave velocity and density models. We implemented a petrophysical approach to combine the kernels of both methodologies in a single process. The synthetic experiments show that jointly inverted models recover shear wave velocity and density better than separate inversions. In particular, density models benefit from the good vertical resolution of surface wave dispersion data, while shear velocity models benefit from the good lateral resolution of gravity data. We also proposed two methods to stabilize the solution when using high-grade polynomials. We applied the methodology to the Los Humeros Geothermal area to demonstrate its applicability in a complex geological scenario. Compared with separate inversion, the joint inversion contributes to enhancing key aspects of the geothermal system by (i) delimitating better the geometry of the caldera deposits in the first 0–2.8 km deep by increasing the vertical resolution in density, (ii) delimitating better the lateral borders of low-Vs bodies at different depths interpreted as a part of a complex magmatic chamber system and (iii) estimating the local shear wave velocity–density relationship that conforms to other known relationships for sedimentary and igneous rocks but with some differences that bring us additional information.

A bathtub model with nonlinear velocity–density relation

The bathtub model is an applicable and effective tool for simulating the characteristics of traffic dynamics in downtown areas during morning rush hour, especially the characteristics of hypercongested traffic. In order to reduce the complexity of the research, previous studies have adopted a linear velocity–density relationship. This has limitations in analyzing the cost and duration of hypercongestion in traffic dynamics. In this paper, we develop a bathtub model with one kind of nonlinear velocity–density Relation, i.e., Pipes–Munjal Relation, based on continuous scheduling preferences and analyze its solutions in both no-toll user equilibrium and social optimum states. Due to the intractability in solving this bathtub model, there exists local analytical solutions, but for a complete solution of the model, only numerical solutions are available. The results indicate that as the value of n increases, the model can simulate traffic dynamics with higher cost and longer duration of hypercongestion under equilibrium, and can simulate traffic states with lower system cost under social optimum. We also explore the results of implementing optimal time-varying toll to realize social optimum. This study expands the relevant theories of bathtub models and provides a new perspective for traffic congestion.

Nonreciprocal interactions in crowd dynamics: Investigating the impact of moving threats on pedestrian speed preferences

Nonreciprocal interaction crowd systems, such as human–human, human–vehicle, and human–robot systems, often have serious impacts on pedestrian safety and social order. A more comprehensive understanding of these systems is needed to optimize system stability and efficiency. Despite the importance of these interactions, empirical research in this area remains limited. Thus, in our study we explore this underresearched area, focusing on scenarios where nonreciprocity plays a critical role, such as mass stabbings, which pose a substantial risk to public safety. We conducted the first experiments on this system and analysed high-accuracy data obtained from these experiments. Specifically, we conduct laboratory experiments on three scenarios: single exits, dual exits, and obscured chases. Then, we introduce an equation to describe the mechanism behind a direct threat zone, which significantly affects pedestrian behaviour. The extent of the direct threat zone is determined by the speed of the moving threat and the radius of danger occurrence. The equation can provide insights for different nonreciprocal interaction crowd systems, where the subjects of the nonreciprocal interactions can be a pedestrian, an autonomous robot or a vehicle. We further categorize potential threats into direct, adjacent, and rear-view zones, quantifying the level of threat for pedestrians. Our study revealed that a pedestrian’s desired velocity correlated positively with potential threat intensity, increasing until near the direct threat zone. An emerging steady state is observed when escape routes are blocked by moving threats. This deviation affects the density–velocity relationship, making it distinct from the general relationship. This deviation signifies unique pedestrian behaviour in the presence of moving threats. Additionally, the rate of change in the angle for pedestrian motion in various desired directions is synchronized. This indicates the emergence of collective intelligence in nonreciprocal interaction crowd systems. As a result, our study may constitute a pioneering step towards understanding nonreciprocal interactions in crowd systems through laboratory experiments. These findings may enhance pedestrian safety and inform not only government crowd management strategies but also individual self-protection measures.

Experimental study on the movement characteristics of adversarial people in the corridor

With the continuous development of pedestrian dynamics, the movement characteristics of multiple types of people (elderly, children, disabled people, etc.) under various scenarios (flood, fire, special building structure, etc.) have been extensively and deeply studied. The relevant conclusions and movement rules are of great significance for guiding the design of building structures and crowd evacuation instructions. However, there is a lack of research on the movement of adversarial crowds with different movement purposes and strong interactions. The analysis of its movement characteristics and the movement modelling of interaction rules need to be further explored through controlled experiments. Therefore, this paper focuses on the study of the movement characteristics of the adversarial crowd and carries out a realistic experiment in which pedestrians in the corridor escape from attackers to complete the evacuation. The purpose was to address the following questions: the impact of attackers and corridor width on pedestrian movement. It was found that the attacker's movement pause would increase the desired velocity of the crowd, and thus the velocity-density relationship was different from the traditional fundamental diagram. The width of the corridor has a great impact on the movement speed and the collision probability of the crowd. Based on the results of the experiment, a model was established and simulation experiments were carried out by changing the width of the corridor. It is hoped that the results of this paper can provide help for emergency evacuation guidance for pedestrians in the future.

Deriving Vp velocity and density properties of complex litho-structural units from the analysis of geophysical log data: A study from the Southern Apennines of Italy

This study is aimed to define a velocity and density database for the main litho-structural units of the Val d’Agri area of the Southern Apennines (Italy). Here we analyze fifteen digital borehole data comprising sonic log, check shot and density log data with dedicated graphic and statistical tools. We compare velocities acquired with two techniques: check-shots and sonic logging, discussing factors influencing them and their variations with a depth trend. In general, we observe that the comparison between the check shots and the sonic logs velocities gives consistent results. The detailed analysis of well logs and velocity distribution histograms, allow us to distinguish the following eight litho-structural units and their representative velocities and densities: Liguride tertiary flysches; Apennine Carbonate Platform, Lagonegro - Clastics, Lagonegro -Carbonates; Irpinia 1; Irpinia 2 and 3; Volturino foredeep turbidites; Apulian Carbonate Platform. The density values were calculated through the velocity density relationship using the Gardner equation, and subsequently compared with the measured density values. The comparison shows good correlations with the adopted Gardner coefficient of a = 0.30 and an exponent m = 0.25 for carbonatic succession, while a Gardner coefficient of a = 0.25 and an exponent m = 0.28 for clastic lithologies.The obtained results represent a key input for the future velocity and gravity modellings and for the time to-depth conversion of seismic reflection profiles, describing the vertical and lateral lithological heterogeneities between carbonate platforms, deep-sea basinal units and clastic/turbidite successions in the complex tectonic settings of the Southern Apennines.The approach applied in this work, based on a shared analytical and graphical analysis of borehole data, can be readily extended to other case studies worldwide, being the analyzed formations lithologically comparable to many other fold-and-thrust belt rocks.

Passenger Queuing Analysis Method of Security Inspection and Ticket-Checking Area without Archway Metal Detector in Metro Stations

In order to avoid the congestion in front of the entrance gate units, it is necessary to analyse and optimise the queuing situation at the planning and design stage. The security inspection area and the ticket-checking area were jointly considered, and a queuing congestion analysis method was proposed. Firstly, the research problem was stated. Then, the problem of calculating the number of passengers in each subarea at any time was transformed into the problem of calculating the transit time of each passenger in each subarea. The transit time was divided into basic transit time and additional transit time. Based on the velocity-density relationship, a quantisation method for basic transit time was proposed related to passenger arrival time. The additional transit time was determined by the moment when the passengers left the subarea according to the sequence of arrival of passengers, the number of queuing passengers in the subarea and the congestion of the subarea to be entered. Finally, the queuing situation of passengers in each subarea at any moment was obtained through passenger flow recursion. Examples showed that the proposed method can deal with multiple working conditions and avoid the tedious and time-consuming scene construction process of the microsimulation software.

Road tolling problem on a two-link parallel network based on the fundamental diagram

This paper studies a road tolling problem in which a road user travels from A to B either via road 1 by paying or via road 2 without charge. The route choice also obeys the user-equilibrium principle. However, the travel time is formulated as a strictly increasing function of the density through the velocity–density relationship or fundamental diagram, which significantly improves the formulation in the classical traffic assignment problem. Accordingly, the influence of toll rate on the road users, the administration department and the road runner is analyzed in detail, by assuming that the user demand is rigid and maximizing the total traffic flow and the runner’s benefits from the collection of toll fees.

Interpretation of gravity and magnetic data in the Central Indian Ocean

The crustal deformation in the Central Indian Ocean is due to major undulations of the oceanic crust, longitudinal fracture zones, and sea-floor topography. The gravity and magnetic data along with six long profiles across the Central Indian Ocean Basin on W–E tracks between 6°S – 1°S latitudes and 77°E – 90°E longitudes are used to study this deformation. It has been observed that the crustal depths obtained from spectral analysis of gravity and magnetic data are in good agreement with 2D forward gravity modelling results which supports seismic results. The computed seismic velocities for the sediments are 2.0 – 5.7 km/s and 6.1 – 7.7 km/s for the oceanic igneous layer and 8.3 – 8.5 km/s for the oceanic upper mantle are used to determine the densities of oceanic crust with the velocity-density relationship. The average basement depths for all the gravity and magnetic profiles are obtained as ~5 km with deviations of about 1 – 2 km from the mean and for the deeper marker, the crustal depths vary from 9 km to 12 km. In the case of curie isotherm, the crustal depths vary from 9 km to 12 km for all magnetic profiles which may indicate deformation. The crustal top depths vary in the range of 3.5 – 8 km (3.2 – 6 km) and the bottom depth varies in the range of 8.2 – 13.5 km (8.5 – 13 km) for magnetic field anomaly data using the spectral method (the Werner method). The crustal top depths vary in the range of 3.6 – 6.5 km and the bottom depth varies in the range of 7.5 – 11.5 km for free-air anomaly data using the spectral method. The above depths are almost correlated with interpreted 2D gravity modelling and available Seismic results.

EFFECT OF THREE-WHEELED VEHICLES ON THE CAPACITY OF A TRAFFIC STREAM

Due to the tremendous development of the number and types of vehicles and a large number of traffic congestions, the phenomenon of the spread of three-wheeled vehicles, which is characterized by ease of movement, has recently appeared in Iraq because of a small space it occupies for its movement. The increase in their numbers exceeds the number of heavy vehicles in most urban areas in Iraq. Therefore, the current study has been devoted to studying the effect of those vehicles with three tires using a simulation program that has been previously developed and has been calibrated to suit the normal sections where the characteristics of these vehicles were included in terms of speed and length. Different ratios were used, ranging from (0-15) % for the first lane only. Some general traffic characteristics were examined, such as velocity-flow and flow-density and density-velocity relationship. The results showed that the presence of this type of vehicle has a significant impact on reducing road efficiency and increasing traffic congestion. The study recommends that a particular lane with a width of 2m on both directions of the roads be designated for the movement of these vehicles and keep them away from interference in the traffic flow of other cars.

Verification of Gardner's equation and derivation of an empirical equation for anhydrite rocks in Sirte basin, Libya: case study

Bulk density is a physical property of rocks measured in the laboratory on rock samples or obtained from oil field logging tools. When bulk density is not measured, a synthetic bulk density log can be calculated, for which Gardner's equation is the most widely used. However, Gardner's equation might not be appropriate for regions in which the density–velocity relationship does not conform to Gardner's curves. Here, we verified the applicability of Gardner's equation to calculation of synthetic bulk density of anhydrite rocks in the Sirte Basin (Libya) and compared the results to those obtained from an equation derived from the available measured bulk density and sonic logs. We used fifteen wells to calibrate Gardner's equation and three wells to derive an equation for the anhydrite rocks. The anhydrite rocks were 10–510 feet thick. The bulk density calculated by Gardner's equation differed only slightly from the measured log values, with the exception of the eastern part of the Sirte Basin. The average of the differences in bulk density between the measured values and Gardner's equation results were 0.022–0.040 g/cm3, and between the measured values and the derived equation results 0.002–0.045 g/cm3, both with a standard error of about 0.01 of the bulk density estimated results. We conclude that while Gardner's equation is more appropriate for estimating the bulk density of anhydrite rocks in the eastern part of the basin, the derived equation could be more appropriate for the western region.

Generation mechanism and simulation research of zipper phenomenon of pedestrian flow in corridor

In this study, the unidirectional pedestrian flow in the corridor is taken as a research object, the generation mechanism of the pedestrian zipper phenomenon is analyzed, and a velocity correction model based on the Voronoi diagram is established for the simulation research. First, the generation mechanism of the pedestrian zipper phenomenon is analyzed from the perspective of optimal visual field and walking comfort of pedestrians. Then the visual attention and visual occlusion of pedestrians are used to describe the factors which affect the zipper deviation during pedestrian movement, the local density of pedestrians is used to describe the walking comfort of pedestrians, the zipper sensitivity coefficient is adopted to describe the willingness of pedestrians to move objectively, and the mechanism of lateral deviation of a single pedestrian is considered to obtain the optimal deviation position of pedestrians. Besides, the Voronoi diagram is introduced to effectively determine the pedestrians surrounding the target pedestrian within the visual field. And the influence of surrounding pedestrians with different distances and directions on the moving velocity of the target pedestrian based on the Voronoi diagram is considered. Then, a velocity correction model of pedestrians based on the Voronoi diagram is constructed, whether the pedestrian has a subjective willingness to deviate is considered, and the deviation rule is embedded to simulate and reproduce the zipper phenomenon of pedestrians. The simulation results truly reproduce the normal pedestrian flow through the corridor and show that our model can overcome the deficiency of the jitter and overlap phenomenon of the traditional social force model. The self-organized pedestrian flow with uniform distribution and the pedestrian zipper effect can also be observed. Furthermore, through the simulation results, we can see that the number of zipper layers for pedestrians is proportional to the width of the corridor. The comparison of simulated pedestrian data with the empirical data indicates that the fundamental diagram of velocity-density relation of our model is in good agreement with the empirical data. A comparison between with and without considering the zipper effect shows that the larger the proportion of pedestrians actively willing to laterally deviate, the more helpful it will be to improve the moving velocity, comfort and space utilization of pedestrians in the corridor.

Fuzzy Social Force Model for Pedestrian Evacuation under View-Limited Condition

Pedestrian evacuation dynamics in a classroom is always a complex process influenced by many fuzzy factors. It is very difficult and inappropriate to quantify the impact of these fuzzy factors by using the mathematical formula. Existing microscopic simulation models have made many efforts to use accurate mathematical method to model the fuzzy interaction behaviors between pedestrians under the view-limited condition. This study tries to fill this gap by establishing a microscopic simulation model which can represent the fuzzy behaviors of pedestrians under view-limited condition. The developed fuzzy social force model (FSFM) combines fuzzy logic into conventional social force model (SFM). Different from existing models and applications, FSFM adopts fuzzy sets and membership functions to describe the pedestrian evacuation process. Seven fuzzy sets are defined for this process, such as stop/go, moving direction, desired force, force from obstacles, force from pedestrian, force from indicators, and acceleration. Membership function of each input factor is calibrated based on the observed data. Model performance is verified by comparing speed distribution, velocity-density relationship, and results of simulation and observation evacuation time. Besides, the proposed model is applied to assess the number and space distribution of exit indicators and stickers. By comparing simulation results with existing models, the paper concludes that FSFM is able to well reproduce pedestrian movement dynamics in real world under view-limited condition.

Macroscopic Modelling of Pedestrian Flows Based on Conservation Law

Overcrowded of sidewalks can reduce the level of satisfaction of pedestrians. The large crowd on the sidewalks results in slowing down time of the pedestrian to arrive in their destination. This studt, focuses on pedestrian flows modelling using the macroscopic model. Numerical approximation of the macroscopic model is formulated as scalar hyperbolic conservation laws. The Lax-Wendroff scheme is used to discretize the equation of conservation laws. The simulation results show that the numerical approximation in term of density confirms the exact solution. In this simulation, the velocity function is obtained by curve fitting of observation data using linear regression method. The observation data, which are consist of velocity-density relation, are obtained from observation of pedestrian flows. The study case of this research conducts on the sidewalks of Braga Street, Bandung, Indonesia. There are two velocity functions used in the simulation, i.e. c 1 = 0.58206 + −0.94476ρ and c 2 = 0.59926 + −0.78052ρ, respectively. In performing the velocity function c 2, the pedestrian leader position is approximately 1 meter in front of the pedestrian leader using the velocity function c 1 at final time T = 20 seconds and T = 30 seconds. Overall, the numerical experiment shows that the pedestrian leader using the velocity functions c 2 is faster than by using c 1.

Experimental study on pedestrians’ uni- and bi-directional movement on staircases under emergency conditions

Staircases are main vertical evacuation passages in multi-story buildings characterized by different pedestrian flow from horizontal passages, such as corridors. Experiments were conducted to investigate crowd ascending and descending dynamics with different numbers of pedestrians in both uni- and bidirectional scenarios. Evacuation processes were recorded by video cameras and velocity sensors, and movement parameters were extracted from the recordings. Typical evacuation features on the staircase such as overtaking behavior, queuing behavior, repelling behavior, and packed and staggered motion mode are observed. The study explores velocity on the staircase as well as the fundamental diagram of velocity–density relationship. Experimental results show that ascending pedestrians could move upwards faster than descending pedestrians under emergency conditions. The stair landing can provide a wide and flat place for pedestrians to accelerate in unidirectional evacuation cases, but has a negative effect on evacuation velocity in bidirectional flow. The distribution of velocity in bidirectional evacuation is more convergent than in the unidirectional scenario. The study findings enrich evacuation modeling and improve the assessment of the pedestrians’ performance on staircases.

A new heuristics model of simulating pedestrian dynamics based on Voronoi diagram* *Project supported by the National Natural Science Foundation of China (Grant Nos. 71771013 and 71621001), in part by the National Key Research and Development Program of China (Grant No. 2019YFF0301403), in part by the Singapore Ministry of Education (MOE) AcRF Tier 2 (Grant No. MOE2016-T2- 1-044), and in

A new heuristics model based on the Voronoi diagram is presented to simulate pedestrian dynamics with the non-crowded state, in which these mechanisms of preference demand evading and surpassing, microscopic anti-deadlock, and site-fine-tuning are considered. The preference demand describes the willingness determination of detouring or following other pedestrians. In the evading and surpassing mechanisms, in order to achieve a balance between avoiding conflicts and minimizing detour distances, a new pair of concepts: “allow-areas and denial-areas” are introduced to divide the feasible region for pedestrians detour behaviors, in which the direction and magnitude of detour velocity are determined. A microscopic anti-deadlock mechanism is inserted to avoid deadlock problem of the counter-directional pedestrian. A site-fine-tuning mechanism is introduced to describe the behavior of avoiding getting too close to the neighbors in pedestrian movement. The presented model is verified through multiple scenarios, including the uni- or bi-direction pedestrian flow in the corridor without obstacles, the uni-direction pedestrian flow in the corridor with obstacles, and the pedestrian evacuation from a room with single-exit. The simulation results show that the velocity–density relationship is consistent with empirical data. Some self-organizing phenomena, such as lanes formation and arching are observed in the simulation. When pedestrians detour an obstacle, the avoiding area before the obstacle and the unoccupied area after the obstacle can be observed. When pedestrians evacuate through a bottleneck without panic, the fan-shaped crowd can be found, which is consistent with the actual observation. It is also found that the behavior of following others in an orderly manner is more conducive to the improvement of the overall movement efficiency when the crowd moves in a limited space.

A geophysical perspective on the lithosphere–asthenosphere system from Periadriatic to the Himalayan areas: the contribution of gravimetry

The structure of the lithosphere–asthenosphere system as imaged from the complementary inversion of seismological and gravimetric data can provide significant clues to understand the processes of orogeny and cratonization and to better formulate the theory of plate tectonics within a sound geodynamic context. In this paper, we review some studies sharing a common synergic methodology that uses the geometry of cellular shear-wave velocity models of the crust and uppermost mantle to constrain a 3D density model obtained by means of linear inversion of gravimetric data. These studies, which were applied to selected areas along an ideal stream running from the Periadriatic region to the Himalayas, despite having different resolution, show some basic common features in the density distribution of the upper mantle whose unveiling may be precluded to gravity models achieved by assuming velocity–density relationships. In fact, one of the main conclusions of the discussed studies is that lithospheric slabs under the investigated orogenic belts, as identified by seismic wave velocity, are, as a rule, not marked by high density. This fact casts serious doubts about the effectiveness of slab-pull and confirms one of the key issues of polarized plate tectonics, mostly fuelled by tidal drag.

True-amplitude versus trace-normalized full waveform inversion

SUMMARY Full waveform inversion (FWI) is a powerful method to estimate high-resolution physical parameters of the subsurface by iteratively minimizing the misfit between the observed and synthetic seismic data. Standard FWI algorithms measure seismic misfit between amplitude-preserved seismic data (true-amplitude FWI). However, in order to mitigate the variations in sources and recording systems acquired on complex geological structures and the physics that cannot be modelled using an approximation of the seismic wave equation, the observed and synthetic seismic data are normalized trace-by-trace and then used to perform FWI. Trace-by-trace normalization removes the amplitude effects related to offset variations and only keeps the phase information. Furthermore, trace-by-trace normalization changes the true amplitude difference because of different normalization factors used for the corresponding synthetic and observed traces. In this paper, we study the performance of true-amplitude FWI and trace-normalized-residual-based FWI in the time domain. The misfit function of trace-normalized-residual-based FWI is defined such that the adjoint source used in gradient calculation is the trace-normalized seismic residual. We compare the two inversion schemes with synthetic seismic data simulated on laterally invariant models and the more complex 2-D Marmousi model. In order to simulate realistic scenarios, we perform the elastic FWI ignoring attenuation to noisy seismic data and to the synthetic data modelled using a viscoelastic modelling scheme. Comparisons of seismic data and adjoint sources show that trace-by-trace normalization increases the magnitude of seismic data at far offsets, which are usually more cycle-skipped than those at near offsets. The inverted results on linear-gradient models demonstrate that trace-by-trace normalization increases the non-linearity of FWI, so an initial model with sufficient accuracy is required to guarantee the convergence to the global minimum. The inverted results and the final seismic residuals computed using seismic data without trace-by-trace normalization demonstrate that true-amplitude FWI provides inverted models with higher accuracy than trace-normalized-residual-based FWI, even when the unknown density is updated using density–velocity relationship in inversion or in the presence of noise and complex physics, such as attenuation.

Crustal thickness over the NW Pacific and its tectonic implications

Igneous emplacement on the NW Pacific oceanic crust via mantle activity, such as hot spots and mantle plumes, results in perturbations of crustal thickness. Therefore, mapping crustal thickness variations is key for understanding these mantle structures and processes. Improvements in resolution and accuracy of marine gravity anomalies promote the use of Moho gravity inversion effects, especially for large-scale applications. For improving the Moho gravity inversion accuracy, density variations of the lithospheric mantle are modelled via lithospheric age-temperature-density relationship since age grid with a resolution of 2 arc-minutes is available, and density variations of the mantle beneath lithosphere are modelled via seismic wave velocity-density relationship since velocity structure with penetration to 700 km is available. Comparisons between the Moho geometries by gravity inversion and seismic interpretation demonstrate that the mantle density modelling improves the Moho inversion accuracy. Our crustal map shows that (1) the crustal thickness of 26% of the NW Pacific region is thicker than 7 km; (2) the southern end of the Emperor seamounts was emplaced on the western flank of the Hess Rise, and a part of the central Hawaiian seamounts was emplaced on the eastern end of the Mid-Pacific Mountains; (3) the magma production of Hawaiian seamounts is greater than that of the Emperor seamounts; (4) the leakiness of the fracture along which the Line Islands formed decreases in the order of the central, southern and northern segments.