面向高密度地震动观测的ARM信号采集系统

地震动观测是地震烈度速报与地震预警的前提和基础。而高密度台站是地震动观测的重要发展方向之一。高密度地震动观测背景下,如何在不影响其计量性能的前提下,降低硬件成本是亟待解决的问题。针对此问题,以ARM处理器为核心设计了一种高精度、多通道、低成本的信号采集系统,它以CPLD作为协处理器,控制24 bit AD进行8通道同步信号采集,并对信号进行必要的预处理,之后CPLD将AD采集的信号存储在FIFO中,由ARM控制FIFO,读出FIFO中存储数据传输给ARM。通过实验数据的分析,信号采集系统的电压噪声均方根小于25μV,其动态范围大于107 d B。

Numerical simulation of ground motion amplification in Modong area, Lushan

The April 20,2013,Ms 7.0 Lushan Earthquake was a major earthquake that followed the Ms 8.0 Wenchuan Earthquake on May 12,2008.Frequent earthquakes have caused heavy casualties and property loss in Western Sichuan.Earthquake disasters are often closely related to the amplification effect of ground motion.Studying the ground motion characteristics of near-surface geological structures helps to understand the distribution of potential earthquake disasters.In this study,we investigated ground motion amplification in the downtown area of Lushan using numerical simulation and aftershock data from the Lushan Earthquake.Using the Lushan earthquake aftershock data from nine seismic stations distributed in the area,the amplification effect of the sites was determined using the"reference site spectral ratio"method.The results show that the frequency of the ground motion amplification in the area was in the range 5–10 Hz,and the corresponding amplification peak was from 3 to 14.Among the study sites,the amplification(14 times)at L07 was the most prominent.To study further the amplification characteristics,shear-wave velocity models for the structures under these sites were established using passive-source Rayleigh surfacewave exploration.One-dimensional(1 D)and two-dimensional(2 D)seismic amplification effects were simulated using horizontally propagating shear-wave modeling.Except Site L07,the 1 D simulation results of each site well reflected the variation feature of the seismic amplification on the frequency band below the observed peak frequency,although the overall simulated amplification peaks were smaller than the observed results.The 2 D simulation of the remarkable amplification phenomenon at L07 was in better agreement with the observation result than was the 1 D simulation,indicating that the seismic amplification in the Modong area is influenced by lateral variation of the Quaternary sediments.

The effect of mining face＇s direction on the observed seismic activity

A major natural hazard associated with LGOM （Legnica-Glogow Copper Mining） mining is the dynamic phenomena occurrence, physically observed as seismic tremors. Some of them generate effects in the form of relaxations or bumps. Long-term observations of the rock mass behaviour indicate that the degree of seismic hazard, and therefore also seismic activity in the LGOM area, is affected by the great depth of the copper deposit, high-strength rocks as well as the ability of rock mass to accumulate elastic energy. In this aspect, the effect of the characteristics of initial stress tensor and the orientation of considered mining panel in regards to its components must be emphasised. The primary objective of this study is to answer the question, which of the factors considered as ＂influencing＂ the dynamic phenomena occurrence in copper mines have a statistically significant effect on seismic activity and to what extent. Using the general linear model procedure, an attempt has been made to quantify the impact of different parameters, including the depth of deposit, the presence of goaf in the vicinity of operating mining panels and the direction of mining face advance, on seismic activity based on historical data from 2000 to 2010 concerned with the dynamic phenomena recorded in different mining panels in Rudna mine. The direction of mining face advance as well as the goaf situation in the vicinity of the mining panel are of the greatest interest in the case of the seismic activity in LGOM. It can be assumed that the appropriate manipulation of parameters of mining systems should ensure the safest variant of mining method under specific geological and mining conditions.

Verification of Parameters of Major Historical Earthquakes in the North Yellow Sea

Based on existing historical data and observations from the Dalian seismic station,this paper rechecks the parameters of the three historical earthquakes of 1916,1917 and 1944 in the North Yellow Sea,near the Yalu River region.The results show that their relocated epicenters are located at contemporarily intense seismic active zones,consistent with the results derived from the data of the Dalian seismic station.The results are valuable in both revising earthquake catalogues and understanding the local background seismicity.

The Rhythm of Earthquake Activity and an Analysis on the Earthquake Tendency of the World, the Chinese Continent and North China

Based on the Morlet complex wavelet transformation,the authors put forward a kind of new method for distinguishing periods of seismic activity and quietude and a new physical thought on the time-dependent wavelet accumulation energy spectrum with periods, the time-frequency distribution of wavelet vibration period spectrum and period-specific wavelet vibration spectrum. By applying the above methods to a time series which is composed of earthquake accumulation energy per year for the world, the Chinese continent and North China, respectively, we obtained some new information about the rhythm of shallow earthquake activity. Considering the historic earthquakes and the rhythm characteristics of current strong earthquake activity, the earthquake tendency in the next years is discussed.

A Discussion on the Generality of Precursor Waves on Well Water Level Records

Taking five underground water level observation wells with high earthquake response capability and located in Shanxi,Hebei and Inner Mongolia as study objects,this paper studies and discusses the generality of precursor waves in well water levels before strong earthquakes. It is indicated that the precursor waves often happen before strong earthquakes,with the ratio of occurrence up to 65% ( 41 /63 ) ; the precursor waves have poor generality in different observation wells,which may be related to the different well-aquifer system of different observation wells and the different source parameters of earthquakes. Compared to the seismic water level fluctuations in a single well,the number of precursor wave times recorded in well water levels before strong earthquakes is slightly less than that of seismic water level fluctuations,with a ratio between 39. 7% and 50. 7%, respectively. The number of observation wells with precursor wave recordings before earthquakes accounts for up to 66. 7% of the total number of observation wells. The precursor wave in well water level records has a certain generality in terms of the number of times recorded and the spatial distribution,except for its manifestation characteristics.

A Discussion on Fault Activity Based on Cross-fault Observations in the Capital Circle Region of China and Its Relationship with Earthquakes

In this paper, we made a systematic study on more than 40 years of observational data of ten temporary fault-crossing measurement sites in the capital circle region of China. We calculated horizontal and vertical components of fault slip, and horizontal extension or compression components. Considering the tectonic characteristics of the capital circle region and regional seismicity, we analyzed the present fault activity of the capital circle region and the relationship with earthquakes. The results show the complexity of fault activity in the region： the level of activity of all faults is low, most faults are left-lateral strike-slip faults; there is less vertical activity than horizontal activity and crustal movement is controlled by horizontal movement; fault activity and earthquake activity have a certain relationship, regional fault activity increases before an earthquake, and fault activity has certain abnormal features before strong earthquakes.

A Study on the Characteristics of Anomalies and Their Dynamic Relationship before the April 14, 2010 M_S 7.1 Yushu Earthquake

The authors studied the seismic activity, precursory anomalies and abnormal animal behavior before the April 14, 2010 Ms 7.1 Yushu earthquake. Analysis showed that anomalies were not rich before the Ms 7.1 Yushu earthquake, but prominent anomalies were observed, such as the long and mid-term trend anomaly characterized by the seismic quiescence of Ms6. 0, MsS. 0 and Ms4.0 earthquakes, and the anomalies in precursor observation of surface water temperature in Yushu and Delingha and electromagnetic measurement in Ping＇an. There were a large number of animal behavior anomalies appearing one week before the earthquake. An M4.7 earthquake occurred 130 minutes before the main shock. In this paper, we studied the dynamic process of the Yushu earthquake preparation using the earthquake focal mechanism solutions on the Bayan Har block boundary since 1996. The results show that the Kalakunlun M7.1 earthquake in 1996, the Mani M7.5 earthquake and the Yushu Ms7.1 earthquake have the same dynamic process. Long and mid-term trend anomalies may be related to the dynamics of evolution of different earthquakes. This paper also discusses the recurrence interval of strong earthquakes, foreshock identification and precursor observation of the Yushu Ms7. 1 earthquake.