The Computation Of Apparent Stress And Its Scaling Law And Analysis Of Spatial And Temporal Distribution

In order to get some information about the stress state of earth crust of capi-tal region of China, we calculate spectral parameters of 117 earthquakes which wererecorded by capital region earthquake network. These parameters include: apparentstress, stress drop, corner frequency, seismic moment and rapture radius. We selectthe records that have epicenter distance less than 200km to ensure higher signal-to-noise waveform, and each event must be recorded by at least 4 stations. We calculatethese spectral parameters from the horizontal component of S wave. Firstly, transformwaveform from time domain to frequency domain, and then use lag-FFT to get morestable results. We consider the geometry e?ect and inelastic attenuation in focal spectraadjusting. The low ?at level and corner frequency is calculated by genetic algorithmby finding a pair of low ?at level and corner frequency which minimize the deviationbetween theory and real spectra. Earthquake radiated energy can be calculated by in-tegrating the real focal spectra and apply a high frequency compensation to it. Anearthquake which listed in NEIC broadband energy catalog was chosen , it happened inMay 17th, 2008, 32.240?N,104.982?E. It turn out that the result is reliable.The result indicate that the value of apparent stress is between 0.2MPa and4.5MPa, mostly between 0.1MPa and 1MPa, and the apparent stress does not vary withseismic moment. Combining this result and NEIC energy catalog, it come to the con-clusion that apparent stress does not increase with seismic moment in 8 (1013?1021Nm)orders of seismic moment. The relation between seismic moment and local magnitudeis lg M0 = 1.27ML + 10.1, the relation of corner frequency and seismic moment islg fc = ?0.302 lg M0 + 4.79, the relation between earthquake radiated energy and localmagnitude is lg Es = 1.56ML + 4.31, the relation between rapture radius and seismicmoment is lg M0 = 2.38 lg r + 8.0. The relation between seismic moment and radiatedenergy e?ciency was also analyzed. Radiated energy e?ciency increases with seismicmoment if seismic moment relative low, and decreases when seismic moment relative high. This character of relation between radiated energy e?ciency and seismic momentconsist with velocity weakening module, which was analyzed by Chaw with numericalsimulation.The curve of apparent stress versus time was got by rolling average method. Itindicates that the average apparent stress vary between 0.2MPa and 2MPa, apparentstress decreased and stayed stable after a max in April 2004, it increased to anotherpeak in the first half of 2005, then suddenly failed to minimum value of the whole re-search time period, The WenAn Ms5.1 earthquake was happened in this lowest period.TangShan area was analyzed because one half of the earthquakes happened in there.The apparent stress of capital region and TangShan area have the following same char-acteristics: (1) bigger earthquakes happened under low apparent stress background (2)apparent stress was enhanced before bigger earthquake will happen (3) the characteris-tics of apparent stress varies with time are similar. The spatial distribution of apparentstress was got by rolling average method. It indicates that the high value of apparentstress locates in northern TangShan, southern-west of XingTai and ZhangJiaKou, andthe max value located in XingTai. Generally speaking, the central part of capital regionhave lower apparent stress value, while the edge area have higher value, the low appar-ent stress value is surrounded by higher apparent stress value. The spatial distributionof the raw value was also analyzed, and found that the distribution of apparent stressis relatively uniform in ZhangJiaKou area and random in other region. The results cano?er a reference about stress status of capital region.