Automatic onset phase picking for portable seismic array observation

Automatic phase picking is a critical procedure for seismic data processing, especially for a huge amount of seismic data recorded by a large-scale portable seismic array. In this study is presented a new method used for automatic accurate onset phase picking based on the proporty of dense seismic array observations. In our method, the Akaike＇s information criterion （AIC） for the single channel observation and the least-squares cross-correlation for the multi-channel observation are combined together. The tests by the seismic array observation data after triggering with the short-term average/long-term average （STA/LTA） technique show that the phase picking error is less than 0.3 s for local events by using the single channel AIC algorithm. In terms of multi-channel least-squares cross-correlation technique, the clear teleseismic P onset can be detected reliably. Even for the teleseismic records with high noise level, our algorithm is also able to effectually avoid manual misdetections.

Strong motion observations and recordings from the great Wenchuan Earthquake

The National Strong Motion Observation Network System （NSMONS） of China is briefly introduced in this paper. The NSMONS consists of permanent free-field stations, special observation arrays, mobile observatories and a network management system. During the Wenchuan Earthquake, over 1,400 components of acceleration records were obtained from 460 permanent free-field stations and three arrays for topographical effect and structural response observation in the network system from the main shock, and over 20,000 components of acceleration records from strong aftershocks occurred before August 1, 2008 were also obtained by permanent free-field stations of the NSMONS and 59 mobile instruments quickly deployed after the main shock. The strong motion recordings from the main shock and strong aftershocks are summarized in this paper. In the ground motion recordings, there are over 560 components with peak ground acceleration （PGA） over 10 Gal, the largest being 957.7 Gal. The largest PGA recorded during the aftershock exceeds 300 Gal.

Microzoning Study for Seismic Risk Reduction in the Areas Covered Soft Soil Deposit, Japan

Kanagawa Prefecture, Japan, is just located on the tectonic plate boundary between the Philippines Sea Plate and the North American Plate. This tectonic plate boundary is called Sagami Trough and located in Sagami Bay. The 1923 Great Kanto Earthquake （Mj7.9） occurred on this plate boundary sub-ducting from Sagami Trough, the damage due to this earthquake was so huge in Kanaawa Pref., especially, along the big river, called Sagami River, located at the middle part of Kanagawa Pref. which was mostly seriously damaged. It is caused by the soft soil deposit along the Sagami River. So, in this study, we first confirmed the results of single point microtrcemor observation of about 980 points in the target area, and at this time, we tried to investigate the surface soil structure by using the miniature array microtrcemor observation, and aimed to estimate the overall ground structure of Sagami Plain. The ground structure of Sagami plains is complex, but the northern part of the plain is relatively simple and soft soil layer is shallow and stable. But the plains of the southern part, especially the west side of the Sagami River were found to be fairly soft ground. Following above, the surface soil structure in north-south direction is very clearly changed depending on the distance from the sea coast. A changing gap on the basement is very quickly appeared about 10 km far from the coast. And also, we calculated the average Vs of the surface ground and confirmed the consistency with the current ground state while confirming the historical change and the topography situation.

Preliminary Analysis for Ground Structure around Source Region of 2008 Iwate-Miyagi Nairiku Earthquake

To obtain a detailed model of the three-dimensional ground structure, the microtoremor and gravity surveys were carried out around Kurikoma area, Japan, where is the source reagion of 2008 Iwate-Miyagi nairiku earthquake and is located about 90 km north of Sendai. Using the microtremor data, velocity structures of shallow sediments are estimated and the results at some of the sites are reported preliminarily. We could not find the detailed velocity structure to bedrock, because small arrays for the microtremor observation were applied, However, significant structures are observed for shallow velocity structure at some sites. Furthermore, gravity data provided Bouguer anomaly, which is one of gravity anomalies, around the target area. From the Bouguer anomaly, area with low anomaly is tbund around the south-eastern area of the fault plane.

Development and Prospect of Study on Soil Nonlinear Dynamic Characteristics under Strong-Motion

Ground motions are significantly influenced by dynamic characteristics of overburden soil layers near ground surface,as thick and soft soil layers would obviously amplify the ground motion strength. The conventional research method on soil nonlinear dynamic characteristics under strong motions is based on experiments in laboratories for the deficiency of observation data,but it is difficult to reliably simulate the complex factors of soils in actual earthquake durations,including loading paths,boundary conditions,and drainage conditions. The incremental data of the vertical downhole observation array,which is comprised of at least one observation point on ground surface and one observation point in a downhole rock base, makes it possible to study soil nonlinear dynamics according to in situ observation data,and provides new basic data and development opportunities to soil nonlinear dynamics studies.

Vibration characteristics of frozen soil under moving track loads

Vibration due to moving traffic loads is an important factor which induces frozen soil damage; this paper analyzed these vibration characteristics of frozen soil foundation under track loads. Firstly, seismic observation array （SOA） technology was applied to monitor the three dimensional dynamic characteristics of frozen soil under movable track load in a per- mafrost region and seasonal frozen soil area. Secondly, a numerical simulation for the response of frozen soil under movable track load was performed based on finite element analysis （FEA）, The results show that dynamic characteristics of frozen soil in perpendicular and parallel direction of the track are obviously different. In the direction perpendicular to the track, the vertical acceleration amplitude had an abrupt increase in the 9-10 m from the track line. In the direction parallel to the track, the acceleration in vertical and horizontal direction had a quick attenuation compared to the other direction. Lastly, various parameters were analyzed for the purpose of controlling the dynamic response of frozen soil and the vibration attenuation in frozen soil layer.

脉冲星计时阵列观测的随机背景信号对标量诱导引力波的限制

最近,NANOGrav、PPTA、EPTA和CPTA合作组各自独立报告了关于随机引力波背景的观测证据.尽管根据观测推断的引力波背景(幅度、频谱)与超大质量双黑洞并合的预言相一致,但这一观测也为搜寻宇宙早期的新物理现象提供了新的窗口.本文探讨了用早期宇宙中的标量诱导引力波来解释这一信号的可能性.作者采用参数化的拐折幂律谱作为随机引力波背景能谱的普适性描述,利用NANOGrav、PPTA和EPTA的新数据和贝叶斯推断的方法进行研究.本研究结果可以约束诱导引力波能谱的相关参数,并进一步对可能在早期宇宙中产生原初黑洞的各种暴胀模型给出限制,这些模型有望在未来的空间引力波观测实验中得到检验.

纳赫兹引力波对单态暗物质模型中电弱相变的影响

受脉冲星定时阵列合作组最近观测到的纳赫兹级随机引力波证据的启发,本文在标准模型的单态扩展中探讨了利用极端过冷的电弱相变解释这些观测结果的可能性,并考虑了相变对于暗物质的影响.研究结果表明,通过精细调节模型参数,相应的渗透温度可以连续降低到1 GeV甚至更低.在如此低的渗透温度下,单态暗物质可能在电弱相变之前就脱离热平衡,从而从热辐射中冻结出来.因此,相变期间产生的熵可以显著影响暗物质的残留密度.这减轻了单态扩展模型中同时解释重子生成和满足暗物质直接探测限制的压力,暗示着所考虑的新物理模型可能存在更广阔的参数空间,并可在未来的实验中得到验证.