On July 20, 1995 an M_L= 4.1 earthquake occurred in Huailai basin, northwest of Beijing, with epicenter coordinates 40.326°N, 115.448°E and focal depth 5.5 km. Following the main shock, microseismicity sharp...On July 20, 1995 an M_L= 4.1 earthquake occurred in Huailai basin, northwest of Beijing, with epicenter coordinates 40.326°N, 115.448°E and focal depth 5.5 km. Following the main shock, microseismicity sharply increased in the basin. This earthquake sequence was recorded by Sino-European Cooperative Huailai Digital Seismograph Network (HDSN) and the hypocenters were precisely located. Using 8 aftershocks as empirical Green(s function (EGF) we calculated the source time function (STF) of the ML=4.1 event respectively, and by superposing these results, we obtained the average time function which has better signal to noise ratio. The final result shows that the ML=4.1 earthquake consisted of two events, one of which was stronger, the other was weaker, STFs from each station demonstrate an obvious (seismic Doppler effect(. Through a trial-and-error method, the following results were drawn: for the 1st event, the rupture length is 0.44 km, rupture velocity is 4.0 km/s, while for the 2nd event those parameters are 0.25 km, 3.0 km/s, the two events ruptured in the direction of 140° and 90° respectively (measured from the strike of the fault, anticlockwise positive), the two events were separated by 0.57 km in space, and 0.09 s in time. Using single EGF, we also retrieved the source time function of other 13 events with ML(2.1 in the Huailai earthquake sequence. These results were reached: each of the 13 events consisted of single event, with the duration of the source time functions ranging between 0.05～0.16 s. Using far-field ground displacement measurement method, the scalar seismic moment, stress drop and rupture radii of 25 events with 0.95(ML(4.1 were obtained. The trend that scalar seismic moment and stress drop increase with magnitude was obvious. In the magnitude range 0.9(ML(2.4, the obtained radii show no correlativity with magnitude, we tend to believe, in such small magnitude range, precise measurement for radii of such small events is beyond the data used in this study.展开更多
The soil constituents and relations between the variation of soil resources and plant communities in three adjacent sites representing the overgrazing, reclamation and comparatively undisturbed communities respectivel...The soil constituents and relations between the variation of soil resources and plant communities in three adjacent sites representing the overgrazing, reclamation and comparatively undisturbed communities respectively were quantified and examined in study area in Huailai Basin, Hebei Province, China. There have been significantly greater constituent of C, N, P in the soils of shrubland site. Corg, Ntotal, Navail and Pavail were between 1.18 and 3.90 times more concentrated in the soils of shrubland site in comparison with the other two sites. Although the Ptotal concentration was lower in shrubland soils than in overgrazed rangeland soils, the Pavail concentration, however, was significantly greater in the soils of shrubland site, and increased by 59.1% and even 289.6% in the soils of shrubland site comparing to those in the soils of range-land and millet field sites. Among the three sites, CV exceeding 40% were found for SO4, Cl, and F ion. The CV of organic carbon also exceeded 40% but only in the soils of millet field site. The highest CV were found for F, SO4 ion in the soils of shrubland and overgrazed rangeland sites, while for Cl and SO4 ion in those of millet field site. The results also showed that the introductions of shrubs are of vital importance for the accumulation of soil nutrients and maintenance of soil fertilities, and also for the restoration and reconstruction of desertified ecosystems.展开更多
The northern boundary fault of Huailai-Zhuolu basin,Hebei Province,has a total length of 58 km and a general strike of NE.The geometry and feature of activity of the 5 segments of the fault greatly differ from each ot...The northern boundary fault of Huailai-Zhuolu basin,Hebei Province,has a total length of 58 km and a general strike of NE.The geometry and feature of activity of the 5 segments of the fault greatly differ from each other.17 paleoseismic events have been recognized within 11 trenches excavated along the different segments of the fault.It is found that each segment is characterized by its distinct recurrence of paleoearthquakes.The recurrence intervals of strong earthquakes for each segment are 3500-7000 a for the shortest and 17,000-20,500 a for the longest.However,the recurrence interval of strong earthquakes for whole fault ranges between 750-8500 a.The boundary of the segments can be recognized as the junction,gap,bending,jog and salient of the fault.The length of the segment ranges between 7.5-14 km.展开更多
基金National Key Basic Research Project "Mechanism and Prediction of Continental Strong Earthquakes".
文摘On July 20, 1995 an M_L= 4.1 earthquake occurred in Huailai basin, northwest of Beijing, with epicenter coordinates 40.326°N, 115.448°E and focal depth 5.5 km. Following the main shock, microseismicity sharply increased in the basin. This earthquake sequence was recorded by Sino-European Cooperative Huailai Digital Seismograph Network (HDSN) and the hypocenters were precisely located. Using 8 aftershocks as empirical Green(s function (EGF) we calculated the source time function (STF) of the ML=4.1 event respectively, and by superposing these results, we obtained the average time function which has better signal to noise ratio. The final result shows that the ML=4.1 earthquake consisted of two events, one of which was stronger, the other was weaker, STFs from each station demonstrate an obvious (seismic Doppler effect(. Through a trial-and-error method, the following results were drawn: for the 1st event, the rupture length is 0.44 km, rupture velocity is 4.0 km/s, while for the 2nd event those parameters are 0.25 km, 3.0 km/s, the two events ruptured in the direction of 140° and 90° respectively (measured from the strike of the fault, anticlockwise positive), the two events were separated by 0.57 km in space, and 0.09 s in time. Using single EGF, we also retrieved the source time function of other 13 events with ML(2.1 in the Huailai earthquake sequence. These results were reached: each of the 13 events consisted of single event, with the duration of the source time functions ranging between 0.05～0.16 s. Using far-field ground displacement measurement method, the scalar seismic moment, stress drop and rupture radii of 25 events with 0.95(ML(4.1 were obtained. The trend that scalar seismic moment and stress drop increase with magnitude was obvious. In the magnitude range 0.9(ML(2.4, the obtained radii show no correlativity with magnitude, we tend to believe, in such small magnitude range, precise measurement for radii of such small events is beyond the data used in this study.
文摘The soil constituents and relations between the variation of soil resources and plant communities in three adjacent sites representing the overgrazing, reclamation and comparatively undisturbed communities respectively were quantified and examined in study area in Huailai Basin, Hebei Province, China. There have been significantly greater constituent of C, N, P in the soils of shrubland site. Corg, Ntotal, Navail and Pavail were between 1.18 and 3.90 times more concentrated in the soils of shrubland site in comparison with the other two sites. Although the Ptotal concentration was lower in shrubland soils than in overgrazed rangeland soils, the Pavail concentration, however, was significantly greater in the soils of shrubland site, and increased by 59.1% and even 289.6% in the soils of shrubland site comparing to those in the soils of range-land and millet field sites. Among the three sites, CV exceeding 40% were found for SO4, Cl, and F ion. The CV of organic carbon also exceeded 40% but only in the soils of millet field site. The highest CV were found for F, SO4 ion in the soils of shrubland and overgrazed rangeland sites, while for Cl and SO4 ion in those of millet field site. The results also showed that the introductions of shrubs are of vital importance for the accumulation of soil nutrients and maintenance of soil fertilities, and also for the restoration and reconstruction of desertified ecosystems.
文摘The northern boundary fault of Huailai-Zhuolu basin,Hebei Province,has a total length of 58 km and a general strike of NE.The geometry and feature of activity of the 5 segments of the fault greatly differ from each other.17 paleoseismic events have been recognized within 11 trenches excavated along the different segments of the fault.It is found that each segment is characterized by its distinct recurrence of paleoearthquakes.The recurrence intervals of strong earthquakes for each segment are 3500-7000 a for the shortest and 17,000-20,500 a for the longest.However,the recurrence interval of strong earthquakes for whole fault ranges between 750-8500 a.The boundary of the segments can be recognized as the junction,gap,bending,jog and salient of the fault.The length of the segment ranges between 7.5-14 km.
