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We provide high‐resolution seismic imaging of the central Garlock fault using data recorded by two dense seismic arrays that cross the Ridgecrest rupture zone (B4) and the Garlock fault (A5). Analyses of fault zone head waves and P‐wave delay times at array A5 show that the Garlock fault is a sharp bimaterial interface with P waves traveling ∼5% faster in the northern crustal block. The across‐fault velocity contrast agrees with regional tomography models and generates clear P‐wave reflections in waveforms recorded by array B4. Kirchhoff migration of the reflected waves indicates a near‐vertical fault between 2 and 6 km depth. The P‐wave delay times imply a ∼300‐m‐wide transition zone near the Garlock fault surface trace beneath array A5, offset to the side with faster velocities. The results provide important constraints for derivations of earthquake properties, simulations of ruptures and ground motion, and future imaging studies associated with the Garlock fault. Plain Language Summary Along the northern edge of the Mojave Desert, the Garlock fault intersects the San Andreas fault and is the second largest (∼300 km long) fault in Southern California. It can host M > 7 earthquakes that pose significant seismic hazard to densely populated communities. However, the subsurface structure of the Garlock fault is not well understood due to the sparse seismic network and lack of seismic activity nearby. The 2019 Ridgecrest earthquake sequence in the Eastern California Shear Zone led to a rapid deployment of several dense linear arrays with ∼100 m spacing and apertures of a few kilometers, which cross the Ridgecrest rupture zone and also the Garlock fault. The recorded seismic data is used here to illuminate the internal structure of the central Garlock fault. Analyses of P‐wave delay times and waves refracted along and reflected by the fault interface indicate a near‐vertical Garlock fault that separates two distinctive crustal blocks with different wave speeds. The resolved high‐resolution fault zone image can have important implications for multiple studies associated with the Garlock fault. Key Points We image the central Garlock fault using data of aftershocks of the 2019 Ridgecrest earthquake recorded by two dense linear arrays A P‐wave velocity contrast across the fault (∼5% faster in the north) generates clear fault zone head and reflected waves Kirchhoff migration of P waves reflected by the fault indicates a near‐vertical interface with a sharp impedance contrast

The reflection of time-harmonic waves in a waveguide with a nonlinear boundary stiffness is considered with applications to rods and beams. Incident waves at frequencies that are multiples of a fundamental frequency give rise to reflected propagating and nearfield waves at the same frequencies. An infinite set of equations is developed for the reflection coefficients, which depend on the amplitudes and phases of the incident waves. Nonlinear boundary conditions are applied, and equations is truncated by using the harmonic balance method and solved numerically. The case of zero linear boundary stiffness, i.e. essential nonlinearity, is studied. First, the case where there is only one incident wave is considered. An approximate solution is found when retaining only two reflected waves. Numerical examples are presented, energy being seen to leak into the higher harmonics. The minimum magnitudes of the reflection coefficients of axial and flexural vibrational waves at the fundamental frequency and the maximum energy that can leak into the higher harmonics are determined. Accuracy and convergence when retaining different numbers of reflected harmonics are illustrated. The case of two incident waves is then considered. Multiple incident waves affect the leakage of energy to higher harmonics and can have a significant effect on the reflection coefficient for the fundamental harmonic. With some parameters, a much lower reflection coefficient is obtained for the wave at the fundamental frequency as compared to the case of one incident wave. It is seen that with two incident flexural waves, the reflection coefficients can be multi-valued for certain values of the system parameters. A numerical study is performed to show the region of multiple solutions.

Zeng, C.-S.; Zhan, J.-M., and Hu, W.-Q., 2022. Numerical study on compound-slope seawalls with different types of protective facings. Journal of Coastal Research, 38(1), 182–195. Coconut Creek (Florida), ISSN 0749-0208. The compound seawall is an important infrastructure to protect the coast effectively against tide and wave impacts. In this paper, a hybrid realizable k – ∊/laminar model and a volume of fluid interface capture method were used to study compound-slope seawalls with different types of protective facings. An analytical method was used to separate the incident wave and the reflected wave, and the numerical results for a compound-slope seawall with a hollow-block protective facing structure were verified by experimental results. The monitored wave surface, incident wave, and reflected wave data in the numerical simulation were compared with the experimental results, and the results show that the numerical model can simulate the interaction process of waves and compound-slope seawalls well. Furthermore, a series of numerical simulation studies on compound-slope seawalls under different protective facing structures with different wave heights, wave periods, water depths, and structure slopes was conducted. The results show that the hollow-block protective facings have a significant weakening effect on the reflected wave height, wave run-up, and wave force when the wave is moderate, which is important for the safety of seawall and onshore building structures.

—Deep seismic surveys along profile 5-AP were carried out in the northeastern shelf zone of the Arctic from the Chukchi fold region on the continent to the deep North Chukchi Basin. To process the experimental material of this profile, mathematical modeling based on the time field method was used, as well as the method of migration of fields of refracted and reflected waves recorded at large distances from the source. As a result, with a high degree of reliability, it was possible not only to identify new features of the structure of the Earth’s crust and upper mantle of this region, but also to determine the rheological properties of the material making them up and the degree of its rigidity or plasticity. This made it possible to propose a new model of the possible geodynamic evolutionary history of this region.

The construction of the Rajamandala hydroelectric power plant civil works has experienced critical problems that arise in the implementation process, with the occurrence of cracks cavities conditions in the headrace tunnel locations. We applied the cross-hole seismic tomography to detect important heterogeneities and mechanical proprieties of the formations between two boreholes in this case inferred cracks cavities condition. The seismic source is inside the borehole “a sparker” and the receivers “hydrophones” are in an adjacent one, the sparker is lowered into the borehole one step at the time. Seismic waves, propagating in the tunnel wall rock, spread widely, and are reflected and refracted when encountering interfaces between rocks with different acoustic impedances. Reflected waves returning to the receivers are recorded. After the processing of the first arrivals of the P waves we obtain a cross section of the seismic velocities in between the two wellbores. With the cross-hole seismic tomography, the basis could be provided to the tunnel construction and parameter adjustments to guarantee the construction safety. Our result shown that there is a weak zone above the tunnel with low Vp zone (~1.2 km/s) may be related to weak zone (may be fracture, unconsolidated rock, and fluid-filled rock or landslide caving). Checker-board resolution test is also conducted to determine the tomogram areas that are reliable to be interpreted. Our challenges are we have poor resolution due to not enough raypath. The Cross-hole seismic tomography can effectively and safely guide the excavation of the tunnel section working surface in combination with reconstructed images and excavation technology.

The problem of blocking technogenic fractures with a suspension mixture is relevant in order to prevent additional water inflow to producing wells. The aim of the work is to evaluate the effect of colmatation of a fracture by polymer-dispersed compositions using a mathematical model of transport of a suspension through a fracture. It is assumed that the suspension particles are larger than the size of the pore channels and do not penetrate into the reservoir. To solve the problem, a system of continuum mechanics equations is used. The leading edge of the suspension slug is a contact discontinuity. It is determined that at the moment of the approach of this discontinuity to the end of the fracture, a reflected wave of the volume fraction of particles is formed, which moves towards the flow and characterizes the blocking of the fracture. At the same time, due to the need to maintain the same flow rate and reduction of the size of the fracture, there is a sharp increase in the downhole pressure, which does not allow the fracture to be completely blocked. The maximum blocked fracture size is determined. The obtained estimates are compared with field data.

Blockages in sewers and drains often result in overflows and flooding that cause significant environmental pollution and public health risks, particularly in hospitals, where the consequences can be catastrophic. Due to their low “visibility”, sewers and drains are inherently difficult to monitor and maintain, resulting in a reactive management approach whereby maintenance or repair is carried out only after a system failure has occurred. This paper investigates the feasibility of applying the reflected wave technique, a unique sonar-like monitoring approach capable of identifying changes in the geometry of closed-pipe conduits, as a means of proactive system monitoring. The technique uses a 10 Hz sinusoidal air pressure wave which is transmitted into the drainpipe. When the pressure wave encounters a system boundary, a reflection is generated which alters the measured test pressure response. Analysis of the reflections generated by a changed system boundary, such as the formation of a blockage, can provide information related to the location of that boundary within the system. An experimental setup was developed to simulate a horizontal drain using standard pipework of 100 mm diameter and 70 m length. The technique was able to detect applied blockages with cross-sectional coverage of 30% and 75%, and lengths ranging from 30 mm to 3000 mm. Accuracy was improved when the pressure sensor was positioned closer to the blockage. When the sensor was 3.4 m from the blockage, location estimates were very accurate (−2% to 3% error). At a 14 m distance from the blockage, the error increased to between 4% and 33%. The accuracy of blockage detection and location improved with increasing blockage cross-sectional area and length. Overall, the reflected wave technique could provide a potentially continuous monitoring solution for blockage detection in sewers and drains.

AbstractThe solution of the problem of blocking a technogenic fracture in the reservoir by a suspension mixture is considered. The mathematical model based on the mass conservation laws for the disperse particles and carrier fluid is used. The flow velocity of disperse particles through the fracture is calculated from the Poiseuille law and the carrier fluid outflow to the reservoir is described by Darcy’s law. It is found that the leading front of suspension slug corresponds to a contact discontinuity. It is shown that a reflected wave in the form of a discontinuity of the volume fraction of disperse particles begins to move counter the flow when the front of suspension slug reaches the fracture end and the fracture begins to be blocked up from this end. It is established that the movement of the reverse wave is gradually slowing down; therefore, blocking the entire fracture is turned out to be problematic.

The main purpose of this work was to investigate the performance of heated shock tube (ST) with different pressure ratios and diaphragm positions numerically and experimentally. The numerical model was developed to simulate the fluid flow inside a shock tube test facility located at Qatar University. The shock tube was a cast‐iron hollow tube with 6 m length, 50 mm internal diameter and 10 mm thickness. ST driver and driven sections were filled with helium–argon mixture and air. The driven section was heated up to 150°C using coils. At the middle of the ST, the diaphragm was made of aluminium sheet (0.5 mm) layers. Five different pressure ratios were implemented during the experiment, and performance evaluation depended on the strength of the incident shock Mach number. The inviscid numerical model solver used transient two‐dimensional time‐accurate Navier–Stokes CFD. The model introduced a parametric study regarding three different diaphragm positions (1m, 2m and 3m) and five pressure ratios (6–10) for each position. In addition to yielding the incident and reflected wave Mach number, reflected wave temperature was also considered a shock tube performance indicator. The incident Mach numbers for the diaphragm middle position from the experiment were compared against those conducted from the model, and good matching was observed. The parametric study results showed that at high‐pressure ratios, diaphragm Positions 1 and 3 could generate a 7.4% increase in shock wave Mach number compared with the diaphragm position‐2 model. Moreover, the diaphragm position‐3 model tends to have a 2% increase in the temperature behind the reflected shock wave compared with the other two positions. The parametric study results showed that at high‐pressure ratios, diaphragm Positions 1 and 3 are able to generate a 7.4% increase in shock wave Mach number compared with the diaphragm position‐2 model. Moreover, the diaphragm position‐3 model tends to have a 2% increase in the temperature behind the reflected shock wave compared with the other two positions.

Decrease in arterial compliance leads to an increased pulse pressure, as explained by the Windkessel effect. Pressure waveform is the sum of a forward running and a backward running or reflected pressure wave. When the arterial system stiffens, as a result of aging or disease, both the forward and reflected waves are altered and contribute to a greater or lesser degree to the increase in aortic pulse pressure. Two mechanisms have been proposed in the literature to explain systolic hypertension upon arterial stiffening. The most popular one is based on the augmentation and earlier arrival of reflected waves. The second mechanism is based on the augmentation of the forward wave, as a result of an increase of the characteristic impedance of the proximal aorta. The aim of this study is to analyze the two aforementioned mechanisms using a 1-D model of the entire systemic arterial tree. A validated 1-D model of the systemic circulation, representative of a young healthy adult was used to simulate arterial pressure and flow under control conditions and in presence of arterial stiffening. To help elucidate the differences in the two mechanisms contributing to systolic hypertension, the arterial tree was stiffened either locally with compliance being reduced only in the region of the aortic arch, or globally, with a uniform decrease in compliance in all arterial segments. The pulse pressure increased by 58% when proximal aorta was stiffened and the compliance decreased by 43%. Same pulse pressure increase was achieved when compliance of the globally stiffened arterial tree decreased by 47%. In presence of local stiffening in the aortic arch, characteristic impedance increased to 0.10 mmHg s/mL vs. 0.034 mmHg s/mL in control and this led to a substantial increase (91%) in the amplitude of the forward wave, which attained 42 mmHg vs. 22 mmHg in control. Under global stiffening, the pulse pressure of the forward wave increased by 41% and the amplitude of the reflected wave by 83%. Reflected waves arrived earlier in systole, enhancing their contribution to systolic pressure. The effects of local vs. global loss of compliance of the arterial tree have been studied with the use of a 1-D model. Local stiffening in the proximal aorta increases systolic pressure mainly through the augmentation of the forward pressure wave, whereas global stiffening augments systolic pressure principally though the increase in wave reflections. The relative contribution of the two mechanisms depends on the topology of arterial stiffening and geometrical alterations taking place in aging or in disease.