甘肃礼县新生代玄武岩的特征及其与地震的关系

本文对甘肃礼县新生代玄武岩及邻区超基性、基性岩的岩石特性进行了简要的叙述，并测定了它们的化学成分，同时还在１×１０３ＭＰａ高压下测定了它们的地震波速度。文中还对玄武岩的物源深度及其与地震的关系进行了探讨。     

移动荷载对桥梁动力响应的影响研究——以开裂预应力混凝土简支梁为例

混凝土桥梁在工作过程中会产生裂缝,为分析移动荷载对开裂混凝土桥梁结构刚度的影响,对开裂梁动力响应进行分析。建立简支T梁桥有限元模型,并将移动荷载施加至有限元模型中。根据简支T梁桥破坏横向分布位置和强度的不同,研究不同工况下各梁荷载横向分布及不同移动速度对裂缝扩展宽度的影响。结果表明,数值模拟结果能较好地验证计算模型的准确性;在较大的移动荷载作用下,混凝土开裂,导致结构刚度减小、位移增大;随着移动荷载和速度的增加,开裂时间增加,结构刚度降低,持续时间增加,位移增大,使结构响应呈现明显非线性。     

基于统计学的地震显著平静阈值估计

提出具有统计学意义的地震显著平静阈值估算方法,用于中国大陆及川滇、新疆和华北地区中强震活动分析,在不同区域得到不同起始震级的显著平静阈值范围。结果显示:(1)中国大陆7级、6级和5级地震显著平静的阈值范围分别为3.9—6.2年、7.9—9.6个月和62—70天;(2)川滇地区6级和5级地震显著平静的阈值范围分别为2.1—2.9年和7.0—8.5个月;(3)新疆地区6级和5级地震显著平静的阈值范围分别为2.6—4.0年和8.5—10.5个月;(4)华北地区6级和5级地震显著平静的阈值范围分别为11.7—23.4年和5.2—7.7年。     

汶川8.0级地震的余震触发作用和对断层的应力加卸载作用

采用可变滑动震源模型,计算和研究了汶川M_S 8.0地震产生的应力变化及对后续6次强余震的应力触发作用,并定量分析了汶川地震对附近活动断裂带的库仑应力加卸载作用。结果显示:汶川地震产生的库仑破裂应力变化分布图案复杂性强,主要由发震断裂复杂的空间展布形态以及震源断层活动具有逆冲兼右旋走滑两种性质决定。汶川地震产生的库仑破裂应力变化对多数强余震存在一定的触发作用。汶川地震的发生对附近的断裂带有不同程度的影响,其中青川断裂中段和北段、岷江断裂南段和灌县-江油断裂南段,主要是以强烈的库仑破裂应力加载作用占主导地位,有利于强余震序列的孕育、加速以至于发生;东昆仑断裂带和鲜水河断裂带受到了轻微的应力加载作用;龙泉山断裂带、华莹山断裂带和西秦岭北缘断裂带主要受到了轻微的卸载作用。     

Rapid report of the 8 January 2022 ​MS 6.9 Menyuan earthquake,Qinghai, China

The M_S 6.9 Menyuan earthquake in Qinghai Province, west China is the largest earthquake by far in 2022. The earthquake occurs in a tectonically active region, with a background b-value of 0.87 within 100 ?km of the epicenter that we derived from the unified catalog produced by China Earthquake Networks Center since late 2008. Field surveys have revealed surface ruptures extending 22 ?km along strike, with a maximum ground displacement of 2.1 ?m. We construct a finite fault model with constraints from InSAR observations, which showed multiple fault segments during the Menyuan earthquake. The major slip asperity is confined within 10 ?km at depth, with the maximum slip of 3.5 ?m. Near real-time back-projection results of coseismic radiation indicate a northwest propagating rupture that lasted for ～10 ?s. Intensity estimates from the back-projection results show up to a Mercalli scale of IX near the ruptured area, consistent with instrumental measurements and the observations from the field surveys. Aftershock locations (up to January 21, 2022) exhibit two segments, extending to ～20 ?km in depth. The largest one reaches M_S 5.3, locating near the eastern end of the aftershock zone. Although the location and the approximate magnitude of the mainshock had been indicated by previous studies based on paleoearthquake records and seismic gap, as well as estimated stressing rate on faults, significant surface-breaching rupture leads to severe damage of the high-speed railway system, which poses a challenge in accurately assessing earthquake hazards and risks, and thus demands further investigations of the rupture behaviors for crustal earthquakes.     

Effect of Poissonos ratio on stress state in the Wenchuan MS8.0 earthquake fault

The Wenchuan M_S8.0 earthquake occurred on the Longmenshan fault which inclines at a dip angle exceeding 60 degrees. Since most thrust earthquakes occur on faults with dip angles of about 30 degrees, it is enigmatic why the Wenchuan earthquake occurred on such a steep fault. In this study we use a simple finite element model to investigate how the stress state in the fault changes with the variation of Poisson's ratio. The results show that, with the Poisson's ratio in the fault increasing, the magnitudes of the principal stresses increase and the maximum shear stress decrease, and, especially, the angle between the maximum principal stress and the fault plane decreases, which will enhance the driving force to overcome the frictional resistance on the fault. The increase of Poisson's ratio in the fault may be an important factor to affect the occurrence of the fault earthquakes with large angles between maximum principal stress and fault plane.

     

张北6.2级地震前后地磁Z分量的日变化

利用河北省及邻省、市共１７个地磁台相对观测Ｚ分量资料,总结分析了张北６．２级地震前后的日变化。认为,一次较强地震前可能有多次异常出现,日变反向可作为中短期异常,而后出现的日变低点位移,当分界线连续在某区出现,地震可能进入短临阶段。日变反向的极值区附近和低点位移连续汇集地区可能是未来震中。对于震前出现的多次异常进行追踪预报,可能效果较好。     

Conductivity of NaCl solution at 0.4–5.0 GPa and 25–500 °C

NaCI-H₂O is the most fundamental ternary system in geology. Until now, the measurements of electrical conductivity of NaCl solutions are still little at high pressures (> O.5 GPa) We measured the conductivity of 0.01 m NaCl solution at 0.4–5.0 GPa and 25-500°C. The results are consistent with that of Quist and Marshall (1968) at 0.4 GPa. The conductivity of NaCl solution increases with increasing temperature. The results also show that the conductivity of NaCl solution changes little with increasing pressure below 1.5 GPa and changes rapidly with increasing pressure above 1.5 GPa. The rapid increase of the conductivity of NaCl solution may play an important role in many geological processes (such as the genesis of ore deposits under hydrothermal condition) and other fields. Project supported by the National Natural Science Foundation of China.     

Early J2 basalts in SE China: Incipience of large-scale late Mesozoic magmatism

Magmatism in SE China was dormant during 204–180 Ma, but was reactivated in 180–170 Ma (early J₂), and then became more and more intensive towards the end of early Cretaceous. The small-scale early J₂ magmatism is the incipience to long-term and large-scale magmatism in this region. A near east-west (EW) trend volcanic belt was distributed across south Hunan, south Jiangxi and southwest Fujian was formed during early J₂ time. Along this belt from the inland toward the coast, the lithology of basalts changes from alkali into tholeiite, and the amount of erupted volcanic rocks and the proportions of rhyolites coexisting with the basalts increase. On the basis of geochemical characteristics of these basalts, we infer that the melting degree of source rocks and the extent of fractional crystallization and crustal contamination all increased whereas the depth of mantle source decreased from the inland to the coast, which led to the variations of geological characteristics of the volcanic belt. In early J₂, the western spreading Pacific plate began to subduct underneath SE China continental block, reactivating near EW trend deep fault that was originally formed during the Indosinian event. The stress of the western spreading Pacific plate and the extent of asthenosphere upwelling increased from the inland to the coast, which is consistent with the generation and evolution of early J₂ basalts.