Microtremor-based analysis of the dynamic response characteristics of a site containing grouped earth fissures

In this study,the Beibu earth fissure site in the northeastern part of Weihe Basin,which contains four nearly parallel earth fissures,was studied.A long straight microtremor measuring line,containing 49 measuring points across four earth fissures,was established to investigate the dynamic response of this site using Fourier spectrum,response acceleration spectrum,Arias intensity,and HVSR analyses.The main results are as follows:(1)The fundamental frequencies of 44 measuring points obtained from HVSR analysis are concentrated within 1.67 Hz-2.25 Hz,and the existence of the earth fissures has little effect on the fundamental frequency changes.(2)There is an amplification effect near a single earth fissure.The dynamic responses are large at the measuring points near the earth fissure,and the values decrease with increasing distance from the earth fissure.In areas between two adjacent earth fissures,these values decrease and are even lower than those in sites without amplification effects.(3)In this earth fissure site,the general area(or less affected area)and affected areas were delineated based on the amplification effect.In engineering applications,construction design should avoid these affected areas and existing structures should be reinforced to satisfy the seismic fortification requirements.

Microtremor-based analysis of the dynamic response characteristics of earth-fissured sites in the Datong basin, China

This study conducted microtremor testing along six survey lines that cross three typical earth fissures in the Datong basin to determine the dynamic response characteristics of earth fissure sites with regard to the Fourier amplitude spectrum,response spectrum,and Arias intensity.The results show the following.(1)The predominant frequency of an earth fissure site is mainly affected by the thickness and the shear wave velocity of the soil layer and is minimally effected by the presence of an earth fissure.(2)Earth fissures have a pronounced amplification effect on dynamic response.Fourier amplitude,response acceleration,and Arias intensity are high near an earth fissure and decrease with an increase in distance from the earth fissure,tending toward stability at a distance of 20 m.(3)The area that is seriously affected by this amplification is within 6-8 m of an earth fissure,and the general affected area is farther out than this,to a distance of 25 m.(4)New construction should be avoided in an area affected by the amplification,and existing buildings in general and seriously affected areas need to be reinforced to increase their seismic fortification intensity.

Development characteristics and formation analysis of the Liangjia Village earth fissure in the Weihe Basin,China

Liangjia Village earth fissure,one of the 79 earth fissures along the Kouzhen-Guanshan fault located in the northern Weihe Basin,causes severe damage to buildings and farmlands.Since the late 1950s,40 earth fissures have occurred in a similar east-west(EW)direction parallel to the Kouzhen-Guanshan fault,and a further 39 earth fissures have occurred with north-west,east-north,or north-east orientations intersecting the fault.In this study,a case study of Liangjia Village earth fissure was conducted to investigate the mechanisms of fissure generation in detail.Geotechnical and geophysical methods including measurements,trenching,drilling,and seismic exploration were used to reveal the basic characteristics,geological background,and origin model of the Liangjia Village earth fissure.This earth fissure,with a total length of 800 m in 2014,runs EW parallel to the Kouzhen-Guanshan fault,and it has damaged buildings and farmlands by forming sinkholes,gullies,subsidence,and a scarp.The trenching results indicated that this fissure underwent multi-phase activity.Analysis of geological drilling and shallow seismic profiling results showed that the fissure also possessed characteristics of a synsedimentary fault.Regarding its genesis,the fissure was formed through the combined actions of three factors:an earthquake created the fissure,the Kouzhen-Guanshan fault controlled its development,and loess erosion and groundwater runoff subsequently enlarged the fissure.Regional extension first generated many buried faults along the hanging wall of the Kouzhen-Guanshan fault before seismic activity caused the buried faults to propagate to the surface,where loess erosion and ground-water runoff promoted the formation of the current earth fissure.