Earthquake Seismic Moment, Rupture Radius and Stress-drop from P-wave Displacement Amplitude vs Time Curves

The reliable determination of earthquake source parameters is a relevant task of seismological investigations which ground nowadays on high quality seismic waveforms collected by near-source dense arrays of ground motion sensors. Here we propose a parametric modelling technique which analyzes the time-domain P-wave signal recorded in the near-source range of small-to-large size earthquakes. Assuming a triangular moment-rate function and a uniform speed, circular rupture model, we develop the equations to estimate the seismic moment, rupture radius and stress-drop from the corner-time and plateau level of the average logarithm of the P-wave displacement vs time curves (LPDT). The constant-Q, anelastic attenuation effect is accounted by a post-processing procedure that evaluates the Q-unperturbed moment-rate triangular shape.<br>The methodology has been validated through the application to the acceleration records of the 2016-2017 Central Italy and 2007-2019 Japan earthquake sequences covering a wide moment magnitude range (Mw 2.5 - 6.5) and recording distance < 100 km. After correcting for the anelastic attenuation function, the estimated average stress-drop and the confidence interval (〈∆σ〉=0.60 (0.42-0.87) MPa and 〈∆σ〉=1.53 (1.01-2.31) for crustal and subcrustal events of Japan and 〈∆σ〉=0.36(0.30-0.44) MPa for Central Italy) show, for both regions, a self-similar, constant stress-drop scaling of the rupture duration/radius with seismic moment. The smaller sensitivity of the spatially averaged, time-varying peak displacement amplitude to the radiation from localized high slip patch on the fracture surface, could explain the retrieved smaller average stress-drops for sub-crustal earthquakes in Japan and M>5.5 events in Central Italy relative to previous estimates using spectral methods.<br><br>

Earthquake Seismic Moment, Rupture Radius and Stress-drop from P-wave Displacement Amplitude vs Time Curves

The reliable determination of earthquake source parameters is a relevant task of seismological investigations which ground nowadays on high quality seismic waveforms collected by near-source dense arrays of ground motion sensors. Here we propose a parametric modelling technique which analyzes the time-domain P-wave signal recorded in the near-source range of small-to-large size earthquakes. Assuming a triangular moment-rate function and a uniform speed, circular rupture model, we develop the equations to estimate the seismic moment, rupture radius and stress-drop from the corner-time and plateau level of the average logarithm of the P-wave displacement vs time curves (LPDT). The constant-Q, anelastic attenuation effect is accounted by a post-processing procedure that evaluates the Q-unperturbed moment-rate triangular shape.<br>The methodology has been validated through the application to the acceleration records of the 2016-2017 Central Italy and 2007-2019 Japan earthquake sequences covering a wide moment magnitude range (Mw 2.5 - 6.5) and recording distance < 100 km. After correcting for the anelastic attenuation function, the estimated average stress-drop and the confidence interval (〈∆σ〉=0.60 (0.42-0.87) MPa and 〈∆σ〉=1.53 (1.01-2.31) for crustal and subcrustal events of Japan and 〈∆σ〉=0.36(0.30-0.44) MPa for Central Italy) show, for both regions, a self-similar, constant stress-drop scaling of the rupture duration/radius with seismic moment. The smaller sensitivity of the spatially averaged, time-varying peak displacement amplitude to the radiation from localized high slip patch on the fracture surface, could explain the retrieved smaller average stress-drops for sub-crustal earthquakes in Japan and M>5.5 events in Central Italy relative to previous estimates using spectral methods.<br><br>

Stress Drop, Seismogenic Index and Fault Cohesion of Fluid-Induced Earthquakes

Sometimes, a rather high stress drop characterizes earthquakes induced by underground fluid injections or productions. In addition, long-term fluid operations in the underground can influence a seismogenic reaction of the rock per unit volume of the fluid involved. The seismogenic index is a quantitative characteristic of such a reaction. We derive a relationship between the seismogenic index and stress drop. This relationship shows that the seismogenic index increases with the average stress drop of induced seismicity. Further, we formulate a simple and rather general phenomenological model of stress drop of induced earthquakes. This model shows that both a decrease of fault cohesion during the earthquake rupture process and an enhanced level of effective stresses could lead to high stress drop. Using these two formulations, we propose the following mechanism of increasing induced seismicity rates observed, e.g., by long-term gas production at Groningen. Pore pressure depletion can lead to a systematic increase of the average stress drop (and thus, of magnitudes) due to gradually destabilizing cohesive faults and due to a general increase of effective stresses. Consequently, elevated average stress drop increases seismogenic index. This can lead to seismic risk increasing with the operation time of an underground reservoir.

PULL AND BENDING FORCE CARBON FIBER COMPOSITE

Based on the test data, it can be seen that the average stress value on the carbon fiber composite with the fiber direction of 0 ° -30 ° -60 ° has the highest tensile stress value in the TA 2 specimen, namely 121.439 MPa, the highest strain value in the TA 1 specimen is 0.031, the value The highest modulus of elasticity in the TA 3 specimen is 438,460 MPa, while for the fiber direction 0 ° -45 ° -90 ° the highest tensile stress value in the TB 3 specimen is 670.691 MPa, the highest strain value in the TB 3 specimen is 0.096, the highest elasticity modulus value in the specimen TB1 is 1076,993 MPa.

Prediction of Rotor Burst Using Strain-Based Fracture Criteria to Comply with the Engine Airworthiness Regulation

Relative to the rotor overspeed compliance governed by civil aviation airworthiness regulation, nowadays Area-Average Stress method is commonly used approach. However, in order to effectively apply the Area-Average Stress method in analyzing burst speed, large amount of testing data is needed to define an important element of this method: a correction factor. This prerequisite hinders the use of this method for many companies which have limited test data. Meanwhile, analysis of rotor burst speed based on Strain-based Fracture Criteria using true stress-strain curves and burst tests has been done on the LPT rotor, and a work procedure obtaining the most critical burst speed for certification is proposed. The analysis results, which had a good correlation with test results, showed that Strain-based Fracture Criteria can accurately predict the burst speed considering the most adverse combination of dimensional tolerances, temperature, and material properties, and rotor dimensional growth under the overspeed condition. Both are required by the aircraft engine airworthiness overspeed regulation. Compared to the Area-Average Stress method, Strain-based Fracture Criteria reflects the physical essence of the rotor burst more realistically and can be simply verified without requiring too much test data, therefore it has a good application prospect in the aircraft engine airworthiness.

Prediction of Rotor Burst Using Strain-Based Fracture Criteria to Comply With the Engine Airworthiness Regulation

Relative to the rotor overspeed compliance governed by civil aviation airworthiness regulation, nowadays Area-Average Stress method is commonly used approach. However, in order to effectively apply the Area-Average Stress method in analyzing burst speed, large amount of testing data is needed to define an important element of this method: a correction factor. This prerequisite hinders the use of this method for many companies which have limited test data. Meanwhile, analysis of rotor burst speed based on Strain-based Fracture Criteria using true stress-strain curves and burst tests has been done on the LPT rotor, and a work procedure obtaining the most critical burst speed for certification is proposed. The analysis results, which had a good correlation with test results, showed that Strain-based Fracture Criteria can accurately predict the burst speed considering the most adverse combination of dimensional tolerances, temperature, and material properties, and rotor dimensional growth under the overspeed condition. Both are required by the aircraft engine airworthiness overspeed regulation. Compared to the Area-Average Stress method, Strain-based Fracture Criteria reflects the physical essence of the rotor burst more realistically and can be simply verified without requiring too much test data, therefore it has a good application prospect in the aircraft engine airworthiness.

Characterization of Major Fault Systems in the Kachchh Intraplate Region, Gujarat, India, by Focal Mechanism and Source Parameters

The focal mechanism and source parameters of 41 local earthquakes (Mw 4.0–5.1) that occurred in the Kachchh rift basin, which is seismically one of India’s most active intraplate regions, are determined to characterize various active fault systems in that region. The tectonics in the rift basin are heterogeneous and complex. In the present study, it was found that one-third of the earthquakes exhibit reverse mechanism and three-fourth are either strike slip or have some components of strike slip. Thus, we conclude that transverse tectonics are currently dominant in the Kachchh rift. These transverse faults are preferably oriented in the northeast–southwest and northwest–southeast directions in the eastern and western parts of the rift, respectively. The movement is sinistral and dextral on faults that are oriented in the northeast–southwest and northwest–southeast directions, respectively. These transverse faults are almost vertical (dip&gt;70°) and mostly blind with no surface expressions. Most of the significant faults that strike east–west dip toward the south and are listric. The stress drop of these 41 earthquakes ranges between 2.3 and 10.39 MPa. It was found that the stress drop of earthquakes may depend on the focal mechanism and is independent of focal depths. The average stress drop is found to be the highest (7.3 MPa) for the earthquakes that show a dominant normal mechanism accompanied by strike slip (5.4 MPa) and reverse (4.7 MPa). The average stress drop of the Kachchh intraplate region is 5.3 MPa, which is consistent with other intraplate regions of the world. A conceptual model of the fault system in the Kachchh region is proposed, based on the results obtained in the present study.

Collapse Analysis of Ship Hull Girder Using Hydro-Elastoplastic Beam Model: Part 2

In Part 1 study, a time-domain collapse analysis method of ship hull girder was developed and named FE-Smith method. Hull girder was treated as elastoplastic beam model and Smith’s method was used for collapse analysis of cross sections. A concept of average stress-average plastic strain relationship was introduced so that nonlinear collapse behavior of members can be treated as pseudo strain-hardening/softening behavior. Fluid-structure interaction effects were considered. Uniform cross-section beam was assumed as a most fundamental study. In this Part 2, a container ship is taken as subject model. Not only FE-Smith analysis but also non-linear FE analyses using shell model for collapse parts are performed for comparison purpose. Two types of average stress-average strain curves are considered for FE-Smith analysis, i.e. obtained by Gordo-Soares formulae and by shell FEM. Applicability of FE-Smith method is examined comparing with more precise but time-consuming methods. Some parametric studies are also performed. Wave response will be reported in the next papers.

Predicting the values of average stresses during the ice–water phase transition in mesoporous silicon-based structures in the temperature range 233...273 K

Theoretical model has been developed for predicting the average stress values during melting of water frozen in silicon-based mesoporous structures in the temperature range 233...273 K, caused by the difference in the thermal expansion coeffi cients of the heterogeneity elements in the materials studied. Numerical calculations were carried out using and dependences of the average stress tensor components on the volumetric water content in the mesoporous silicon matrix were investigated.