Distribution of Intra-Crustal Low Velocity Zones beneath Yunnan from Seismic Ambient Noise Tomography

Previous studies have reached consensus that low velocity zones are widespread in the crust beneath Yunnan region. However, the relationships between the low velocity zones and large faults, earthquake distribution are less investigated by available studies. By analyzing the seismic ambient noise recorded by Yunnan Seismic Networks and Tengchong volcano array, we construct a 3D crustal shear wave velocity model for the Yunnan region, which provides more details of the distribution of intra-crustal low velocity zones all over Yunnan. The distribution of low velocity zones shows different features at different depths. At shallow depths, the results are well correlated with near surface geological features. With increasing depth, the low velocity zones are gradually concentrated on the northern part of our study area, most likely reflecting variations in crustal thickness beneath the Yunnan region. The low velocity zones are truncated at depth by several large faults in Yunnan. It is interesting that most strong earthquakes（Ms≥5.0） occurred in Yunnan are distributed in low velocity zones or the transition zones between low and high velocity anomalies within the upper-to-middle crust. The crustal structure is composed of a brittle, seismically active upper-to-middle crust and a warm, aseismic lower crust.

Tensile properties analysis of CFRP-titanium plate multi-bolt hybrid joints

Hybrid joints have better tensile properties than pure bonded and bolted bolts,and are increasingly used in the aerospace field.Tensile tests are carried out for the Hybrid Bonded/Bolted(HBB)joints of Carbon Fiber Reinforced Polymer(CFRP)laminate and titanium alloy plate under different bolt numbers,and the corresponding load–displacement curves are obtained.At the same time,based on Continuum Damage Mechanics(CDM)theory,which is derived from 3D Hashin failure criteria,and a Cohesive Zone Model(CZM),the tensile strength prediction model of the composite laminate-titanium alloy plate multi-bolted HBB joint was established,and the numerical simulation results were in good agreement with the experimental height,which validate the feasibility of the model.The difference in the bearing capacity of HBB joints under different numbers of bolts is compared and analyzed.On this basis,the influence of inter-bolt distance on the tensile properties of the HBB joints is explored.The results show that the double-nail HBB joints can effectively improve the end warpage and low bearing capacity of the single-nail HBB joints.The tensile failure load of the double-nail HBB joints under the standard lap width(30 mm)is 82.6%higher than that of the single nail,the tensile failure load of the three-bolt HBB joints is 34.1%higher than that of the double nail.For the three-bolt HBB joint,the joint strength is controlled by the adhesive and the external bolt,while the internal bolt is redundant,the hybrid joint can be simplified by reducing the middle bolt.The inter-bolt distance has a great influence on the failure load of the hybrid joint.Increasing the inter-bolt distance can effectively improve the bearing capacity of the structure.

Fault Slip Model of 2013 Lushan Earthquake Retrieved Based on GPS Coseismic Displacements

Lushan Earthquake （-Mw 6.6） occurred in Sichuan Province of China on 20 April 2013, was the largest earthquake in Longmenshan fault belt since 2008 Wenchuan Earthquake. To better understand its rupture pattern, we focused on the influences of fault parameters on fault slips and performed fault slip inversion using Akaike＇s Bayesian Information Criterion （ABIC） method. Based on GPS coseismic data, our inverted results showed that the fault slip was mainly confined at depths. The maximum slip amplitude is about 0.7 m, and the scalar seismic moment is about 9.47x10TM N.m. Slip pattern reveals that the earthquake occurred on the thrust fault with large dip-slip and small strike-slip, such a simple fault slip represents no second sub-event occurred. The Coulomb stress changes （ACFF） matched the most aftershocks with negative anomalies. The in- verted results demonstrated that the source parameters have significant impacts on fault slip distri- bution, especially on the slip direction and maximum displacement.

Recovering Period of Postseismic Fluid Pressure in Fault Valve

The present study aims to reveal the recovering period of the postseismic fluid pressure in fault zone, offering an insight into earthquake recurrence. Numerical modeling is performed based on a 2D simple layered fault-valve model to simulate the fluid activities within the earthquake fault. In order to demonstrate the features of postseismic fluid pressure in natural state, the interference of tectonic movements is not considered. The recovering period of postseismic fluid pressure includes a sudden- changing period and a much longer fluctuating period. Modeling results show that fault permeability and porosity are sensitive parameters and reversely proportional to the recovering period of the fluid pressure in earthquake fault zone. When the permeability reduces from 10^-15 to 10^-18 m^2, the recovering period increases from 400 to 2 000 yrs, correspondently. The upper and lower fluid pressures are sepa- rated by the valve seal, causing their fluctuations in opposite tendencies.