The ~3.6 to 3.7 M Paucity in Global Earthquake Frequency: Potential Coupling to Zero Point Fluctuation Force and Quantum Energies

There has been protracted historical evidence of a relative paucity in the distribution frequency of global earthquakes within the M = 3.5 to 4.0 range. We observed a similar phenomenon for all recently recorded earthquakes from January 2009 through August 2013. Frequency distributions with increments of M = 0.1 verified the trough of the diminished incidence to be between M = 3.6 and 3.7 with an abrupt increase between M = 3.9 and 4.0. The calculated equivalent photon wavelength for the energies associated with M = 3.6 approaches Planck’s Length while the related time increment is the cutoff frequency for the Zero Point Fluctuation force coupled to gravity. The conspicuous congruence between Planck’s time and length and the lower than expected frequency based upon Gaussian assumptions of distribution for the discrete band of energy associated with this magnitude range of earthquakes suggests a conduit may exist between intrinsic features of Planck space-time and geophysical processes. The existence of such a connection would encourage alternative explanations for sun-seismic activities as due to solar instabilities. Instead, it may reflect influence upon both from alterations in the structure of space being traversed by the solar system as it moves through the galaxy.

Study on Variation of Fitting Goodness of Relation Between Earthquake Frequency and Magnitude before Moderately Strong Earthquakes (Ms≥5.0)

In this paper,characteristics of spatial and temporal variation of linear fitting goodness before some moderately strong earthquakes(Ms≥5.0)in the eastern part of China(east of longitude 180)are studied according to the famous Gutenberg-Richter’s relation expressed as lgN=a-bM,by using the moderate and small events that occurred in and around the source area.The results show that the linear goodness of fitting varies abnormally prior to these moderately strong earthquakes.In the early stage of the earthquake preparatory process,distribution of the energy released through small events in and around the source area is isostatic and the fitting goodness approximates 1,while the distribution of the energy turns to be isostatic before moderately strong earthquakes,leading to the obvious decrease of the linear goodness of fitting.This phenomenon could be a medium term anomaly and a medium term criterion for moderately strong earthquake prediction.

Continuous-cyclic variations in the b-value of the earthquake frequency-magnitude distribution

Seismicity of the Earth （M ≥ 4.5） was compiled from NEIC, IRIS and ISC catalogues and used to compute b-value based on various time windows. It is found that continuous cyclic b-variations occur on both long and short time scales, the latter being of much higher value and sometimes in excess of 0.7 of the absolute b-value. These variations occur not only yearly or monthly, but also daily. Before the occurrence of large earthquakes, b-values start increasing with variable gradients that are affected by foreshocks. In some cases, the gradient is reduced to zero or to a negative value a few days before the earthquake occurrence. In general, calculated b-values attain maxima 1 day before large earthquakes and minima soon after their occurrence. Both linear regression and maximum likelihood methods give correlatable, but variable results. It is found that an expanding time window technique from a fixed starting point is more effective in the study of b-variations. The calculated b-variations for the whole Earth, its hemispheres, quadrants and the epicentral regions of some large earthquakes are of both local and regional character, which may indicate that in such cases, the geodynamic processes acting within a certain region have a much regional effect within the Earth. The b-variations have long been known to vary with a number of local and regional factors including tectonic stresses. The results reported here indicate that geotectonic stress remains the most significant factor that controls b-variations. It is found that for earthquakes with Mw ≥ 7, an increase of about 0.20 in the b-value implies a stress increase that will result in an earthquake with a magnitude one unit higher.

Study on correlativity among some seismological prediction indexes related to earthquake frequency or energy

Correlation among various seismological prediction indexes related to earthquake frequency N or energy E for describing seismicity changes is studied by seismic data of 11 seismic zones (areas) in the Sichuan-Yunnan region. A statistical test for correlativity shows that seismicity indexes obtained from transformation of earthquake frequency N or energy E have correlation to a certain extent while they are used to describe seismicity changes. If the transformation is linear in all cases, the correlation coefficient is equal to 1. The smaller the transformation deviation from linearity, the bigger the correlation coefficient is.

Critical analysis of the ULF power depression as a possible Tohoku earthquake precursor

Among electromagnetic methods of short-term earthquake prediction,an approach is being actively developed based on the phenomenon of magnetic ultra-low-frequency(ULF)power depression occurring a few days before an earthquake.In particular,a nighttime geomagnetic power depression in the band 0.03-0.05 Hz was observed approximately 5 days before the catastrophic Tohoku 2011 earthquake.To verify the reliability of this method,we performed an extended analysis using data from magnetometer arrays JMA,MAGDAS,PWING,and INTERMAGNET.The selected stations included sites close to the epicenter(<300 km)and remote points(~10000 km).The band-integrated spectral power of nighttime magnetic noise decreased significantly from March 6-9,several days before the earthquake.However,such variations occur simultaneously not only at nearby stations but also at distant stations.During this event,the ULF power depression was caused by low global geomagnetic activity,as evidenced by the planetary index SME.Thus,the depression of geomagnetic ULF noise cannot be considered a reliable short-term precursor.

Typical earthquake-induced soft-sediment deformation structures in the Mesoproterozoic Wumishan Formation, Yongding River Valley, Beijing, China and interpreted earthquake frequency

The Mesoproterozoic Wumishan Formation, composed of dolomite is a widely distributed stratigraphic unit in the Beijing area. It was formed over a long period of time in the Yan-Liao aulacogen, a stable peritidal environment that was ideal for recording earthquakes in the form of soft-sediment deformation structures (SSDS). Numerous examples occur in the upper part of the Wumishan Formation, along the Yongding River Valley. In addition, brittle structures include intrastratal fault and seismically cracked breccias. The soft-sediment deformation structures include liquefied features (diapirs, clastic dykes, convolute bedding), compressional deformation features (accordion folds, plate-spine breccias, mound-and-sag structures), and extensional plastic features (loop-bedding). Based on the regional geological setting and previous research, movements along the main axial fault of the Yan-Liao aulacogen are considered as the triggers for earthquakes since the Early Mesoproterozoic. The number and distribution of the SSDS suggest the major earthquake frequency in the Wumishan Formation of 20 to 32 thousand years.

Preliminary investigation of building damage in Hatay under February 6,2023 Turkey earthquakes

On February 6,2023,an M_(w)7.8 earthquake hit the south of Kahramanmaras prefecture,Turkey,followed by another M_(w)7.5 earthquake after nine hours in the middle region of the Kahramanmaras prefecture.More than 84,000 buildings collapsed or were severely damaged,and more than 50,000 lives were lost in Turkey and Syria.Some of the authors,as members of Chinese rescue team,entered Antakya,Hatay prefecture,and investigated the damaged buildings.This paper first summarizes the damage patterns of buildings and provides three reasons for the massive number of collapsed buildings;i.e.,the lack of seismic measures for better ductility,site effects such as liquefaction and surface rupture,and pronounced low-frequency components of the ground motions.Next,the seismic responses of two typical buildings are calculated based on the geometric data estimated by visual inspection.The results imply that the resonance of the whole structure and the poorer ductility of key members resulted in the collapse of buildings.Finally,some conclusions are drawn.Note that although a large number of buildings were seriously damaged to collapse,the majority of buildings in the areas of extreme shaking were lightly or moderately damaged,which implies that well designed and constructed buildings were able to survive and protect human lives even in over-design earthquakes.

Experimental validation of a signal-based approach for structural earthquake damage detection using fractal dimension of time frequency feature

This article extends a signal-based approach formerly proposed by the authors, which utilizes the fractal dimension of time frequency feature （FDTFF） of displacements, for earthquake damage detection of moment resist frame （MRF）, and validates the approach with shaking table tests. The time frequency feature （TFF） of the relative displacement at measured story is defined as the real part of the coefficients of the analytical wavelet transform. The fractal dimension （FD） is to quantify the TFF within the fundamental frequency band using box counting method. It is verified that the FDTFFs at all stories of the linear MRF are identical with the help of static condensation method and modal superposition principle, while the FDTFFs at the stories with localized nonlinearities due to damage will be different from those at the stories without nonlinearities using the reverse-path methodology. By comparing the FDTFFs of displacements at measured stories in a structure, the damage-induced nonlinearity of the structure under strong ground motion can be detected and localized. Finally shaking table experiments on a 1：8 scale sixteen-story three-bay steel MRF with added frictional dampers, which generate local nonlinearities, are conducted to validate the approach.

A refined Frequency Domain Decomposition tool for structural modal monitoring in earthquake engineering

Output-only structural identification is developed by a refined Frequency Domain Decomposition（rFDD） approach, towards assessing current modal properties of heavy-damped buildings（in terms of identification challenge）, under strong ground motions. Structural responses from earthquake excitations are taken as input signals for the identification algorithm. A new dedicated computational procedure, based on coupled Chebyshev Type Ⅱ bandpass filters, is outlined for the effective estimation of natural frequencies, mode shapes and modal damping ratios. The identification technique is also coupled with a Gabor Wavelet Transform, resulting in an effective and self-contained time-frequency analysis framework. Simulated response signals generated by shear-type frames（with variable structural features） are used as a necessary validation condition. In this context use is made of a complete set of seismic records taken from the FEMA P695 database, i.e. all 44 ＂Far-Field＂（22 NS, 22 WE） earthquake signals. The modal estimates are statistically compared to their target values, proving the accuracy of the developed algorithm in providing prompt and accurate estimates of all current strong ground motion modal parameters. At this stage, such analysis tool may be employed for convenient application in the realm of Earthquake Engineering, towards potential Structural Health Monitoring and damage detection purposes.

Characteristics of frequency content of near-fault ground motions during the Chi-Chi earthquake

The frequency content of earthquake ground motion is very important because it affects the dynamic response of structural systems. In the paper, we use five scalar parameters (the response spectral predominant period Tp, smoothed spectral predominant period To, Fourier amplitude spectral mean period Tm, equivalent pulse period Tv, and the pseudo-velocity spectral predominant period Tpv) reflecting the characteristics of frequency content of strong ground motion to examine the near-fault three-component motions during the 1999 Chi-Chi earthquake. The result indicates that the frequency content of near-fault motions at the Hanging wall is less than that at the foot wall; Tp shows a smaller value than that of To and Tm and it emerges a reverse relation of three-component motions as compared with that of To and Tm; Tv and Tpv of the near-fault motions at the north end of the rupture display a similar trend to that generated by the rupture directivity effect of strike-slip faulting. We therefore conclude that these observations are useful in the formulation of near-fault design spectra for seismic codes and in zoning studies in seismic risk.

Variation of Seismic Frequency in the Yunnan Region After the Indonesia Earthquake With M_S8.7

The seismic frequency increased significantly in the Yunnan region after the Indonesia earthquake with M_S8.7 on December 26, 2004. This was estimated by analyzing the seismic frequency ratio between the influenced and normal times, the spatial distribution characteristics of the increased seismic frequency, the temporal-spatial distribution and types of seismic swarms. Seismic frequency increased at 71.3% of the statistical sites in the Yunnan area. The maximal increase ratio is 18.2.

Synthetic sensitivity analysis of high frequency radiation of 2011Tohoku-Oki(MW9.0) earthquake

Frequency-dependent rupture behavior of sub- duction zone interplate megathrust faults has been observed by back-projection method in different frequency bands （from 0.05 to 5 Hz）. It has been suggested that the down-dip region of the Tohoku megathrust radiated strongly at high frequencies （〉10 Hz） compared with that of the up-dip region. By assuming the same source tirne function of each fault patch, we perform a synthetic sensitivity analysis to compare the energy received from the shallower parts （and further way from the receiver sites） with that frona the deeper parts （and closer to the receiver sites） of the rupture. Our results indicate that regional onshore recordings are probably not adequate to constrain the presence of far-off shore high frequency radiations because of the strong attenuation of this region.

Research on Frequency of the Aftershock Sequence of the Wenchuan Earthquake Based on Coseismic Coulomb Stress Change

By the aftershock frequency estimation method based on the calculation of coseismic static Coulomb stress changes and rate-and state-dependent fault constitutive law,we calculate the frequency of "direct "aftershocks of the Wenchuan earthquake related to coseismic static Coulomb stress changes in its aftershock zone and the areas nearby.It shows that the frequency is significantly lower than the truth in the main rupture zone,especially in the southern rupture zone,due to the decrease of stress level on the rupture plane of the main shock resulting from coseismic Coulomb stress change.The study also shows that the effect of the Coulomb stress change on the duration of aftershock activity is associated with the lower limit magnitude.The duration is about 15-16 months for aftershocks above ML4.0,and close to 60 months for aftershocks above ML3.5.In this period,the ratio of the"direct"aftershocks caused by coseismic Coulomb stress change ranges between 44.7% to48.6%,which suggests that,even in the "effective"period of coseismic Coulomb stress changes,about half of the aftershocks on the main shock rupture plane are independent of coseismic Coulomb stress changes.It is pointed out that those aftershocks may be related to the afterslip or the viscoelastic relaxation,which are time dependent cases.

Site effects by generalized inversion technique using strong motion recordings of the 2008 Wenchuan earthquake

The generalized inversion of S-wave amplitude spectra from the free-field strong motion recordings of the China National Strong Motion Observation Network System （NSMONS） are used to evaluate the site effects in the Wenchuan area. In this regard, a total of 602 recordings from 96 aftershocks of the Wenchuan earthquake with magnitudes of M3.7-M6.5 were selected as a dataset. These recordings were obtained from 28 stations at a hypocenter distance ranging from 30 km to 150 km. The inversion results have been verified as reliable by comparing the site response at station 62WUD using the Generalized Inversion Technique （GIT） and the Standard Spectral Ratio method （SSR）. For all 28 stations, the site predominant frequency F and the average site amplification in different frequency bands of 1.0-5.0 Hz, 5.0-10.0 Hz and 1.0-10.0 Hz have been calculated based on the inversion results. Compared with the results from the horizontal-to-vertical spectral ratio （HVSR） method, it shows that the HVSR method can reasonably estimate the site predominant frequency but underestimates the site amplification. The linear fitting between the average site amplification for each frequency band and the V20 （the average uppermost-20 m shear wave velocity） shows good correlation. A distance measurement called the asperity distance DAspt is proposed to reasonably characterize the source-to-site distance for large earthquakes. Finally, the inversed site response is used to identify the soil nonlinearity in the main shock and aftershocks of Wenchuan earthquake. In ten of the 28 stations analyzed in the main shock, the soil behaved nonlinearly, where the ground motion level is apparently beyond a threshold ofPGA 〉 300 cm/s^2 or PGV 〉 20 cm/s, and only one station coded 51SFB has evidence of soil nonlinear behavior in the aftershocks.

Short-term and imminent geomagnetic anomalies of the Wenchuan M_S8.0 earthquake and exploration on earthquake forecast

The diurnal variation of the geomagnetic vertical component is exhibited mainly by changes of phase and amplitude before strong earthquakes. Based on data recorded by the network of geomagnetic observatories in China for many years, the anomalous features of the appearance time of the minima of diurnal variations （i.e, low-point time） of the geo- magnetic vertical components and the variation of their spatial distribution （i.e, phenomena of low-point displacement） have been studied before the Wenchuan Ms8.0 earthquake. The strong aftershocks after two months＇ quiescence of M6 aftershocks of the Ms8.0 event were forecasted based on these studies. There are good correlativities between these geomagnetic anoma- lies and occurrences of earthquakes. It has been found that most earthquakes occur near the boundary line of sudden changes of the low-point time and generally within four days before or after the 27th or 41st day counting from the day of the appearance of the anomaly. In addition, the imminent anomalies in diurnal-variation amplitudes near the epicentral areas have also been studied before the Wenchuan earthquake.

Doppler effect of the rupture process of the great M_W7.9 Wenchuan earthquake

In this study we performed a classical spectrum analysis of seismic waveforms recorded at far field stations of the great MW7.9 Wenchuan earthquake to observe the shifts of the corner frequency with azimuth due to the Doppler effect.Our results show that this damaging great earthquake had a dominating rupture propagation direction of 64.0°.The equivalent radius of the fault rupture surface was estimated to be 33 km,yielding the rupture area of about 3 500 km2.Thus the length of the rupture fault surface is about 230 km if the depth（or width） extent is 15 km.The computer program developed in this study can quickly provide the information about the source of a future large（damaging） earthquake,which could be very useful for predicting aftershocks and planning the rescue operations.

Fracture characteristics of the 1997 Jiashi,Xinjiang, China, earthquake swarm inferred from source spectra

Broadband P and S waves source spectra of 12 M_s≥5.0 earthquakes of the 1997 Jiashi, Xinjiang, China. earthquake swarm recorded at 13 GDSN stations have been analyzed. Rupture size and static stress drop of these earthquakes have been estimated through measuring the corner frequency of the source spectra. Direction of rupture propaga- tion of the earthquake faulting has also been inferred from the azimuthal variation of the comer frequency. The main results are as follows: ① The rupture size of M_s≥6.0 strong earthquakes is in the range of 10~20 km, while that of Ms_=5.0~5.5 earthquakes is 6~10 km. ② The static stress drop of the swarm earthquakes is rather low, being of the order of 0.1 MPa. This implies that the deformation release rate in the source region may be low. ③ Stress drop of the earthquakes appears to be proportional to their seismic moment, and also to be dependent on their focal mechanism. The stress drop of normal faulting earthquakes is usually lower than that of strike-slip type earth quakes. ④ For each M_s≥6.0 earthquake there exists an apparent azimuthal variation of the comer frequencies. Azimuthally variation pattern of comer frequencies of different earthquakes shows that the source rupture pattern of the Jiashi earthquake swarm is complex and no uniform rupture expanding direction exists.

The Background Variation of Natural Source ELF and Its EM Abnormal Phenomena in Yunnan Earthquakes

In order to add earthquake monitoring methods and develop new method research,the ELF Network for Earthquake Monitoring selected 30 stations in the Capital Circle and the Sichuan-Yunnan region. Finding electromagnetic field background variation is the basis of distinguishing the seismic electromagnetic anomalies. This paper introduces the data acquisition and selection of the Shexian,Anqiu,Lijiang and Dali stations which have recorded for longer time with better data and are located on the similar latitude. Then we use the natural source electromagnetic field's auto-power spectrum to express the intensity of the electromagnetic field. By using power spectral data of many frequencies in the observation frequency band,after the data pre-processing and sliding average noising,the background variation of extremely low frequency stations and the range ability were acquired.Taking the Baoshan M5. 1 earthquake on October 30,2015 and Dali M5. 0 earthquake on May 18,2016 as examples,the authors analyzed the earthquake electromagnetic anomaly characteristic of ELF stations around the earthquakes.

Effects of hanging wall and footwall on demand of structural input energy during the 2008 Wenchuan earthquake

Systematic differences in the duration and frequency content of ground motions from the hanging wall and footwall during the 2008 Wenchuan earthquake are investigated,focusing on the influence of these differences on structural input energy based on the elastic and inelastic energy responses of structures.A comparison of the input energy spectra between the hanging wall and the footwall reveal that the structural input energy on the hanging wall is not amplified due to the short duration and low peak ground velocity to acceleration ratio（V/A）.However,the larger demand of structural input energy on the footwall in the range of medium and long periods is observed and the demand increases up to 50% relative to the average level of structural input energy for rupture distances larger than 30 km.The importance of considering the footwall effect on structural input energy when comparing ground motions in the range of medium and long periods is recognized.

Stress drop assessment of the August 8, 2017, Jiuzhaigou earthquake sequence and its tectonic implications

By using a broadband Lg attenuation model developed for the Tibetan Plateau,we isolate source terms by removing attenuation and site effects from the observed Lg-wave displacement spectra of the M 7.0 earthquake that occurred on August 8,2017,in Jiuzhaigou,China,and its aftershock sequence.Thus,the source parameters,including the scalar seismic moment,comer frequency and stress drop,of these events can be further estimated.The estimated stress drops vary from 47.1 kPa to 7149.6 kPa,with a median value of 59.4 kPa and most values falling between 50 kPa and 75 kPa.The estimated stress drops show significant spatial variations.Lower stress drops were mainly found close to the mainshock and on the seismogenic fault plane with large coseismic slip.In contrast,the highest stress drop was 7.1 MPa for the mainshock,and relatively large stress drops were also found for aftershocks away from the major seismogenic fault and at depths deeper than the zone with large coseismic slip.By using a statistical method,we found self-similarity among some of the aftershocks with a nearly constant stress drop.In contrast,the stress drop increased with the seismic moment for other aftershocks.The amount of stress released during earthquakes is a fundamental characteristic of the earthquake rupture process.As such,the stress drop represents a key parameter for improving our understanding of earthquake source physics.