NEWS

ＮＥＷＳＴｈｅＳｅｃｏｎｄＩｎｔｅｒｎａｔｉｏｎａｌＣｏｎｆｅｒｅｎｃｅｏｎＨｙｄｒｏ－Ｓｃｉｅｎｃｅａｎｄ－Ｅｎｇｉｎｅｅｒｉｎｇ（ＩＣＨＥ－＇９５）ＩＣＨＥ－＇９５ｗａｓｖｅｒｙｓｕｃｃｅｓｓｆｕｌｌｙｈｅｌｄｏｎ２２－２６Ｍａｒｃｈ１９９５ｉｎ...     

Theoretical researches on three-dimensional coda wave scattering problem

Ｔｈｅｏｒｅｔｉｃａｌｒｅｓｅａｒｃｈｅｓｏｎｔｈｒｅｅ－ｄｉｍｅｎｓｉｏｎａｌｃｏｄａｗａｖｅｓｃａｔｔｅｒｉｎｇｐｒｏｂｌｅｍＹｏｎｇ－ＡｎＮＩＥ；ＪｉａｎＺＥＮＧａｎｄＤｅ－ＹｉＦＥＮＧ（聂永安，曾健，冯德益）（ＳｅｉｓｍｏｌｏｇｉｃａｌＢｕｒ...     

State of in-situ stress in different rocks

Ｓｔａｔｅｏｆｉｎ－ｓｉｔｕｓｔｒｅｓｓｉｎｄｉｆｆｅｒｅｎｔｒｏｃｋｓ（朱焕春，陶振宇）Ｈｕａｎ－Ｃｈｕｎ；ＺＨＵａｎｄＺｈｅｎ－ＹｕＴＡＯ（ＷｕｈａｎＵｎｉｖｅｒｓｉｔｙｏｆＨｙｄｒａｕｌｉｃａｎｄＥｌｅｃｔｒｉｃＥｎｇｉｎｅｅｒｉｎｇ，Ｗｕｈａ...     

Study on the feature selection and classifica－tion effect of precursory data of ground tilt

Ｓｔｕｄｙｏｎｔｈｅｆｅａｔｕｒｅｓｅｌｅｃｔｉｏｎａｎｄｃｌａｓｓｉｆｉｃａ┐ｔｉｏｎｅｆｅｃｔｏｆｐｒｅｃｕｒｓｏｒｙｄａｔａｏｆｇｒｏｕｎｄｔｉｌｔＺＨＥＮＧ－ＹＵＡＮＬＩ（李正媛），ＤＥ－ＦＵＣＨＥＮ（陈德福），ＹＩ－ＬＩＮＷＵ（吴奕麟）ａ...     

Effects of magnitude accuracy and complete－ness data on seismic hazard parameters

Ｅｆｆｅｃｔｓｏｆｍａｇｎｉｔｕｄｅａｃｃｕｒａｃｙａｎｄｃｏｍｐｌｅｔｅ┐ｎｅｓｄａｔａｏｎｓｅｉｓｍｉｃｈａｚａｒｄｐａｒａｍｅｔｅｒｓＨＵＩ－ＣＨＥＮＧＳＨＡＯ（邵辉成），ＪＩＡ－ＳＨＵＸＩＥ（谢家树），ＰＩＮＧＷＡＮＧ（王平）ａｎｄＹＡ－Ｘ...     

Contributors to this issue

ＣｏｎｔｒｉｂｕｔｏｒｓｔｏｔｈｉｓｉｓｓｕｅＷａｎ－ＺｈｅｎｇＣＨＥＮＧ（程万正）Ｄｅｐｕｔｙ－ｃｈｉｅｆａｎｄｓｅｎｉｏｒｅｎｇｉｎｅｅｒｏｆｔｈｅＲｅｓｅａｒｃｈＯｆｆｉｃｅＡｎａｌｙｓｉｓａｎｄＰｒｅｄｉｃｔｉｏｎｏｆＥａｒｔｈｑｕａｋｅｉｎ...     

The numerical method of Fourier eigen transform and its application in seismicity analysis

ＴｈｅｎｕｍｅｒｉｃａｌｍｅｔｈｏｄｏｆＦｏｕｒｉｅｒｅｉｇｅｎｔｒａｎｓｆｏｒｍａｎｄｉｔｓａｐｐｌｉｃａｔｉｏｎｉｎｓｅｉｓｍｉｃｉｔｙａｎａｌｙｓｉｓＢＩＮＧＣＨＥＮ１）（陈兵）ＺＨＩ－ＺＨＥＮＺＨＥＮＧ２）（郑治真）ＺＡＩ－ＳＥＮＪＩＡＮＧ...     

Expert system for earthquake prediction（ESEP）（2）－Knowledge representation and evidence combination

Ｅｘｐｅｒｔｓｙｓｔｅｍｆｏｒｅａｒｔｈｑｕａｋｅｐｒｅｄｉｃｔｉｏｎ（ＥＳＥＰ）（２）－ＫｎｏｗｌｅｄｇｅｒｅｐｒｅｓｅｎｔａｔｉｏｎａｎｄｅｖｉｄｅｎｃｅｃｏｍｂｉｎａｔｉｏｎＨｏｎｇ－ＳｈｕｎＦＡＮ（范洪顺）ａｎｄＢｉ－ＱｕａｎＷＡＮＧ（王碧泉...     

Research on the relationship between Earth＇s variable rotation and global seismic activity

ＲｅｓｅａｒｃｈｏｎｔｈｅｒｅｌａｔｉｏｎｓｈｉｐｂｅｔｗｅｅｎＥａｒｔｈ＇ｓｖａｒｉａｂｌｅｒｏｔａｔｉｏｎａｎｄｇｌｏｂａｌｓｅｉｓｍｉｃ　ａｃｔｉｖｉｔｙＤａ－ＷｅｉＺＨＥＮＧａｎｄＹｏｎｇ－ＨｏｎｇＺＨＯＵ（郑大伟，周永宏）（Ｓｈａｎｇｈａｉ...     

Identification method of weak seismic phases on the basis of wavelet packet trans-form

Ｉｄｅｎｔｉｆｉｃａｔｉｏｎｍｅｔｈｏｄｏｆｗｅａｋｓｅｉｓｍｉｃｐｈａｓｅｓｏｎｔｈｅｂａｓｉｓｏｆｗａｖｅｌｅｔｐａｃｋｅｔｔｒａｎｓ－ｆｏｒｍＸＩ－ＱＩＡＮＧＬＩＵ１）３）（刘希强）ＨＵＩ－ＬＡＮＺＨＯＵ１）（周惠兰）ＺＨＩ－ＺＨＥＮＺＨＥＮＧ...     

Dependence of the energy released during earthquake on ambient shear stress

Starting with dislocation model, using the result of the fracture mechanics: the slip displacement at the crack tip is proportional to the length of the crack and the applied ambient shear stressτ ₀ ² , we consider the dislocation in the earthquake to be the slip displacement at the crack tip and have obtained the analysis expresses of displacement and velocity pulse for the circular crack and have calculated the seismic wave energy radiated by earthquake. The seismic wave energyE ∞M ₀ τ ₀ ² f(v) _r , i. e.E is proportional to the seismic momentM ₀ and the square of the ambient shear stressτ ₀ ² and increases with the rupture velocityv _r . In frequency domain, integrating the square of source velocity spectrum derived from our the scaling law model, we have also obtained the seismic wave energyE released by earthquake and earthquake radiated effficiencyη.E ∞M ₀ τ ₀ ² also. If takingτ ₀ = 10.0 MPa, E=4.79M ₀. This result is consistent with the estimate by Vassiliou and Kanamori (1982). Theη=5.26%. The distribution of the seismic wave energy is that most of the energy contains in the frequency range between the first corner frequencyf _c1 and thirdf _c3, amount to 92.3% the energy in the rangef<f _c1 is about 3.85% and 3.85% whenf>f _c3. Thef _c3 is about 8Hz forM ⩾ 6, thus most of radiated energy is below 2Hz. This phenomenon had been verified by Vassiliou Kanamori. Previous results show the energy radiated by earthquake to be strongly dependent on ambient shear stress. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 146–152, 1993. This work was supported by the Deutsche Forschungsgemeinschaft, Bonn, F. R. Germany. The support is grateful acknowledged. The authors are also grateful to Professor Klussmann and Mr. Hasthoff for their lots of help.     

A study on the focal parameters of Shidian M =5.9 earthquake sequences in 2001

On the basis of about 300 earthquake wave forms observed in the Shidian M _S=5.9 sequences on April 12, 2001 recorded in Kunming Digital Seismic Network, the spectra of shear wave have been used to estimate the focal parameters of these earthquake sequences. The results show that within the magnitude range of 1.5–5.3, the seismic moments are 10¹⁰–10¹⁶ N·m, the corner frequencies are 0.2–0.8 Hz, radii of the focal rupture are 200–2 500 m and the stress drops are 0.1×10⁵–20×10⁵Pa. Through the statistical analyses of variation of corner frequency f _c and stress drop Δσ with time, it is discovered that the average corner frequency of the foreshock sequences is obviously lower than that of the aftershock sequences. Contrarily, the average stress drops Δσ of the foreshock sequences are clearly higher than that of the aftershocks. It is considered that these variation characteristics of average corner frequency and stress drops before and after the main shock have index significance to the precursory information before a strong earthquake. The higher stress drops for the foreshock sequences show that the higher shear stresses have been stored in the area of main shock. After the main shock, most of the stresses have been released, so the aftershock sequences show a rupture process of lower stresses. Foundation item: Scientific and Technological Key Project of Yunnan Province (2001NG46)     

Source parameters of the earthquakes of the Baikal rift system

The dynamic parameters of the earthquake source—the seismic moment, the moment magnitude, the source radius, the stress drop, and the amplitude of displacement—are determined by the amplitude Fourier spectra of the body shear waves (S-waves) for 62 earthquakes of the Baikal rift system with the energy class of K _P = 9.1–15.7. In the calculations I used the classical Brune model. The seismic moment of the earthquakes being investigated changes from 3.65 × 10¹¹ N m to 1.35 × 10¹⁸ N m, and the radii of earthquake sources vary from 390 m to 1.84 km. The values of the drop in stress Δσ grow with an increase in the seismic moment up to 1.7 × 10⁸ Pa. For the group of weak earthquakes (M _w = 1.7–3.3), extremely low values of the drop in stress 10³–10⁴ Pa are observed. The maximum amplitude of displacement in the source amounts to 5.95 m. The empirical equations between the seismic moment and the other dynamic parameters of the source are determined. The regional dependence of the seismic moment and energy class is obtained: log M ₀ ± 0.60 = 1.03K _P + 3.17. The character of the relationship between the seismic moment and the corner frequency indicates that the classical scaling law of the seismic spectrum for the earthquakes in question is not fulfilled. The obtained estimates of the dynamic parameters are in satisfactory agreement with the published data concerning the analogous parameters of the other rift zones, which reflects the general regular patterns of the destruction of the lithosphere and the seismicity in the extension zones of the lithosphere.     

Estimation of seismic stress drop from the peak velocity of ground motion

ＥｓｔｉｍａｔｉｏｎｏｆｓｅｉｓｍｉｃｓｔｒｅｓｄｒｏｐｆｒｏｍｔｈｅｐｅａｋｖｅｌｏｃｉｔｙｏｆｇｒｏｕｎｄｍｏｔｉｏｎＪＩＡＺＨＥＮＧＱＩＮ（秦嘉政）ＺＵＹＩＮＬＩＵ（刘祖荫）ＸＩＡＯＤＯＮＧＱＩＡＮ（钱晓东）ＱＩＮＧＹＩＮＸＩＥ（谢庆...     

The regional characteristics of seismic activity in China

ＴｈｅｒｅｇｉｏｎａｌｃｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆｓｅｉｓｍｉｃａｃｔｉｖｉｔｙｉｎＣｈｉｎａＺｈｅｎ－ＬｉａｎｇＳＨＩ，ＪｉａｎＷＡＮＧａｎｄＸｉａｏ－ＤｏｎｇＺＨＡＮＧ（时振梁，王健，张晓东）（ＩｎｓｔｉｔｕｔｅｏｆＧｅｏｐｈｙｓｉｃｓ，Ｓ...     

Review of the source characteristics of the Great Sumatra–Andaman Islands earthquake of 2004

The December 26, 2004 Sumatra–Andaman Island earthquake, which ruptured the Sunda Trench subduction zone, is one of the three largest earthquakes to occur since global monitoring began in the 1890s. Its seismic moment was M ₀ = 1.00 × 10²³–1.15 × 10²³ Nm, corresponding to a moment-magnitude of M _w = 9.3. The rupture propagated from south to north, with the southerly part of fault rupturing at a speed of 2.8 km/s. Rupture propagation appears to have slowed in the northern section, possibly to ∼2.1 km/s, although published estimates have considerable scatter. The average slip is ∼5 m along a shallowly dipping (8°), N31°W striking thrust fault. The majority of slip and moment release appears to have been concentrated in the southern part of the rupture zone, where slip locally exceeded 30 m. Stress loading from this earthquake caused the section of the plate boundary immediately to the south to rupture in a second, somewhat smaller earthquake. This second earthquake occurred on March 28, 2005 and had a moment-magnitude of M _w = 8.5.     

Monitoring the West Bohemian earthquake swarm in 2008/2009 by a temporary small-aperture seismic array

The most recent intense earthquake swarm in West Bohemia lasted from 6 October 2008 to January 2009. Starting 12 days after the onset, the University of Potsdam monitored the swarm by a temporary small-aperture seismic array at 10 km epicentral distance. The purpose of the installation was a complete monitoring of the swarm including micro-earthquakes (M _L < 0). We identify earthquakes using a conventional short-term average/long-term average trigger combined with sliding-window frequency-wavenumber and polarisation analyses. The resulting earthquake catalogue consists of 14,530 earthquakes between 19 October 2008 and 18 March 2009 with magnitudes in the range of − 1.2 ≤ M _L ≤ 2.7. The small-aperture seismic array substantially lowers the detection threshold to about M _c = − 0.4, when compared to the regional networks operating in West Bohemia (M _c > 0.0). In the course of this work, the main temporal features (frequency–magnitude distribution, propagation of back azimuth and horizontal slowness, occurrence rate of aftershock sequences and interevent-time distribution) of the recent 2008/2009 earthquake swarm are presented and discussed. Temporal changes of the coefficient of variation (based on interevent times) suggest that the swarm earthquake activity of the 2008/2009 swarm terminates by 12 January 2009. During the main phase in our studied swarm period after 19 October, the b value of the Gutenberg–Richter relation decreases from 1.2 to 0.8. This trend is also reflected in the power-law behavior of the seismic moment release. The corresponding total seismic moment release of 1.02×10¹⁷ Nm is equivalent to M _L,max = 5.4.     

Source mechanism and source parameters of May 28, 1998 earthquake,Egypt

On May 28, 1998, a moderate size earthquake of mb 5.5 occurred offshore the northwestern part of Egypt (latitude 31.45°N and longitude 27.64°E). It was widely felt in the northern part of Egypt. Being the largest well-recorded event in the area for which seismic data from the global digital network are available, it provides an excellent opportunity to study the tectonic process and present day stress field occurring along the offshore Egyptian coast. The source parameters of this event are determined using three different techniques: modeling of surface wave spectral amplitudes, regional waveform inversion, and teleseismic body waveform inversion. The results show a high-angle reverse fault mechanism generally trending NNW–SSE. The P-axis trends ENE–WSW consistently with the prevailed compression stress along the southeastern Hellenic arc and southwestern part of the Cyprean arc. This unexpected mechanism is most probably related to a positive inversion of the NW trending offshore normal faults and confirms an extension of the back thrusting effects towards the African margin. The estimated focal depth ranges from 22 to 25 km, indicating a lower crustal origin earthquake owing to deep-seated tectonics. The source time function indicates a single source with rise time and total rupture duration of 2 and 5 s, respectively. The seismic moment (M _o) and the moment magnitude (M _w) determined by the three techniques are 1.03 × 10¹⁷ Nm, 5.28; 1.24 × 10¹⁷ Nm, 5.33; and 1.68 × 10¹⁷ Nm, 5.42; respectively. The calculated fault radius, stress drop, and the average dislocation assuming a circular fault model are 7.2 km, 0.63 Mpa, and 0.11 m, respectively.     

Empirical predictors of annual bed load travel distance,and implications for salmonid habitat restoration and protection

Measurements of annual travel distance (L_b) of bed load sediment at 16 locations in Alaska, the intermountain USA, west coast USA and Scotland are strongly correlated with bankfull channel width (r² = 0·86, p < 0·001). Travel distance of particles is probably limited by trapping in bars, which have a longitudinal spacing proportional to channel width. Increased abundance of woody debris reduces bar spacing and may reduce L_b. Longer cumulative duration of bed load transporting flows in a year appears to increase L_b. Other predictors of annual travel distance such as stream power per unit length, drainage area and bankfull discharge were less well correlated with L_b (r² ranging from 0·27 to 0·51). Stream power per unit bed area, basal shear stress and slope were not significantly related to L_b (r² < 0·05). Most correlations were improved when regressions were limited to data from the west coast USA. Travel distance estimates can be used to help identify reaches that may take longer to recover from large, short‐term increases in sediment supply. Published in 2001 by John Wiley & Sons, Ltd.     

The space and time distribution characteristics of the shear stress field for the sequence of the Wuding earthquake

Follow Chen and Duda's model of spectral fall-off of (3, the dependence of peak parameters of ground motion, peak displacement dm, peak velocity vm and peak acceleration am, upon the environment stress (0-values are studied using near source seismic digital recordings for the sequence of the Wuding, Yunnan, M = 6.5 earthquake, in which, as a new thought, the peak parameters are assumed to be related to the medium Q-value. Three formulae for estimating the environment stress (0-values by the peak parameters of three types of ground motions are derived. Using these formulae, the environment stress (0-values are calculated for the sequence of the Wuding earthquake. The result show that (0-values calculated by the three formulae are constant largely, the averages of (0 are in the range of 5.0～35 MPa for most earthquakes. It belongs to the high-stress earthquakes sequence: the high-stress values are restricted to the relatively small area closely near to the epicenter of the main shock. The fine distribution structure for the contours of the environment stress (0-values is related closely to the strong aftershocks. The analysis of spatial and temporal feature of (0-values suggests that the earthquakes sequence in a rupture process generated at the specific intersection zone of seismo-tectonics under high-stress background.