Comparison between different earthquake magnitudes determined by China Seismograph Network

By linear regression and orthogonal regression methods, comparisons are made between different magnitudes (lo-cal magnitude ML, surface wave magnitudes MS and MS7, long-period body wave magnitude mB and short-period body wave magnitude mb) determined by Institute of Geophysics, China Earthquake Administration, on the basis of observation data collected by China Seismograph Network between 1983 and 2004. Empirical relations between different magnitudes have been obtained. The result shows that: 1 As different magnitude scales reflect radiated energy by seismic waves within different periods, earthquake magnitudes can be described more objectively by using different scales for earthquakes of different magnitudes. When the epicentral distance is less than 1 000 km, local magnitude ML can be a preferable scale; In case M<4.5, there is little difference between the magnitude scales; In case 4.5MS, i.e., MS underestimates magnitudes of such events, therefore, mB can be a better choice; In case M>6.0, MS>mB>mb, both mB and mb underestimate the magnitudes, so MS is a preferable scale for deter-mining magnitudes of such events (6.08.5, a saturation phenomenon appears in MS, which cannot give an accurate reflection of the magnitudes of such large events; 2 In China, when the epicentral distance is less than 1 000 km, there is almost no difference between ML and MS, and thus there is no need to convert be-tween the two magnitudes in practice; 3 Although MS and MS7 are both surface wave magnitudes, MS is in general greater than MS7 by 0.2~0.3 magnitude, because different instruments and calculation formulae are used; 4 mB is almost equal to mb for earthquakes around mB4.0, but mB is larger than mb for those of mB≥4.5, because the periods of seismic waves used for measuring mB and mb are different though the calculation formulae are the same.     

ACTA SEISMOLOGICA SINICA Vol. 19 2006 GENERAL CONTENTS

(Translated from the Chinese edition of Vol. 28, 2006) No. 1 Comparison between earthquake magnitudes determined by China seismograph network and US seismograph network (Ⅱ): Surface wave magnitude LIU Rui-feng , CHEN Yuntai, Peter Bormann , REN Xiao , HOU Jian-min , ZOU Li-ye and YANG Hui (1) Characteristics of coda wave attenuation in Yunnan area WANG Wei-jun, LIU Jie and CHEN Ling (8) 3-D rheologic model of earthquake preparation (Ⅲ): Precursor fi…     

Discussion on the Relationship between Different Earthquake Magnitude Scales and the Effect of Seismic Station Sites on Magnitude Estimation

Based on the earthquake catalog reported by the Chinese digital seismic network in recent years, we select the earthquakes with both surface wave magnitude and local magnitude and fit them into a relationship between the two magnitudes. The systematic difference is found from the formula which has been used for 30 years. Because of a large dynamic range and wide frequency range of the current digital observation system, in addition to a larger number of stations and earthquakes being used compared to before, the relation obtained in this paper seems more reliable. Our calculation shows that there is no significant difference before and after magnitude conversion so we suggest the abandonment of magnitude conversion. The site response of a station consists of amplification at different frequencies. The amplification is equal to about 1 and changes little with frequency at stations located on basement rock, and it is greater than 1 at low frequency ranges and less than 1 at high frequency ranges at stations located on sediment layers. The difference between magnitudes from single station located on sediment layer and the average magnitude from the whole network increases from negative to positive with period. It seems that there is no fixed station correction factor and the station correction method does not work to improve the accuracy and magnitude estimates.     

The prediction for seismicity trends of M≥8 in the world by analysis of seismicity patterns

After completion of a study on predicting risky zones of earthquake of M≥8 for 1-3 years in the mainland of China,which was supported by Chinese Joint Seismological Science Foundation(D07018 and D08009),a further study was extended to that of greater magnitudes in the world.Based on the historical earthquake cases,we finished the research report,forecasting global earthquakes with magnitude more than 8.0 using the image analysis of seismicity.In this research report,we summarize 11 abnormal seismicity images for predicting earthquake of M≥8.0 around the world.In our research report,we predicted earthquakes of M≥8.0 from June 2009 to June 2014,the medium term predicting within 5 years period.Among these 5 predictive areas,three earthquakes occurred,which is Samoa M8.1 Earthquake on 29 September 2009,Talca M8.5 Earthquake on 27 January 2010,Chile,and Eastern Sendai M9.0 Earthquake on 11 March 2011,Japan respectively.Here we introduce the main items of the image analysis of seismicity and we predict three earthquakes and think that the image analysis of seismicity can be of help.     

Comparison between earthquake magni-tudes determined by China seismograph network and US seismograph network (II): Surface wave magnitude

Introduction Earthquake magnitude is the most common measure of an earthquake′s size,and is one of the basic parameters of an earthquake.There are three most familiar scales of earthquake magnitude:ML(local earthquake magnitude),MS(surface wave magnitude)and mB/mb(body wave magni-tude).Richter(1935)introduced ML when studying earthquakes in Southern California.In1945,Gutenberg(1945a)put forward surface wave magnitude scale to determine earthquake magnitude(MS)using surface waves(20s)of s…     

Modeling the dynamic process of tsunami earthquake by liquid-solid coupling model

Tsunami induced by earthquake is an interaction problem between liquid and solid.Shallow-water wave equation is often used to modeling the tsunami,and the boundary or initial condition of the problem is determined by the displacement or velocity field from the earthquake under sea floor,usually no interaction between them is consid-ered in pure liquid model.In this study,the potential flow theory and the finite element method with the interaction between liquid and solid are employed to model the dynamic processes of the earthquake and tsunami.For model-ing the earthquake,firstly the initial stress field to generate the earthquake is set up,and then the occurrence of the earthquake is simulated by suddenly reducing the elastic material parameters inside the earthquake fault.It is dif-ferent from seismic dislocation theory in which the relative slip on the fault is specified in advance.The modeling results reveal that P,SP and the surface wave can be found at the sea surface besides the tsunami wave.The surface wave arrives at the distance of 600 km from the epicenter earlier than the tsunami 48 minutes,and its maximum amplitude is 0.55 m,which is 2 times as large as that of the sea floor.Tsunami warning information can be taken from the surface wave on the sea surface,which is much earlier than that obtained from the seismograph stations on land.The tsunami speed on the open sea with 3 km depth is 175.8 m/s,which is a little greater than that pre-dicted by long wave theory,(gh)1/2=171.5 m,and its wavelength and amplitude in average are 32 km and 2 m,respectively.After the tsunami propagates to the continental shelf,its speed and wavelength is reduced,but its amplitude become greater,especially,it can elevate up to 10 m and run 55 m forward in vertical and horizontal directions at sea shore,respectively.The maximum vertical accelerations at the epicenter on the sea surface and on the earthquake fault are 5.9 m/s2 and 16.5 m/s2,respectively,the later is 2.8 times the former,and therefore,sea water is a good shock     

A Review of Catalogues of Chinese Earthquakes

In the past decade, the most authoritative catalogues of Chinese earthquakes and the most popular with seismologists in China are the following:(1) Gu Gongxu, 1983, Catalogue of Chinese Earthquakes;(2) Min Ziqun, 1988, Concise Catalogue of Chinese Earthquakes;(3) Xie Yusuou, 1989, Catalogue of Chinese Earthquakes (M≥ 4.7) from 1900-1980 with Uniform Magnitudes; and(4) Min Ziqun, 1995, Catalogue of Chinese Historical Strong Earthquakes. Earthquakes that occurred before 1900 are mainly documented in historical records.Since 1950s, more recent earthquakes were documented in two major compilations of historical records finished in 1956 and 1983-1987. Separately this effort resulted in two chronicles: two volumes for the first one and five volumes for the second one. The magnitudes are converted from the maximum intensity. These magnitudes, by convention, are connected with surface wave magnitudes. However, it is clear that they do not have any strict seismological definition.The period of 1900-1962 documen     

Change Laws of Intensity of Moderate-Small Earthquakes (2.0≤Ms≤5.5)

The change laws of intensity of nearly 200 moderate-small earthquakes with Ms=2.0~5.5 occurring on the Chinese mainland since 1954 have been analyzed and are compared with that of moderately strong earthquakes(Ms≥5.0).The results show that there is quite obvious regionality in the statistical laws by both moderate-small earthquakes and moderately strong earthquakes:attenuation of intensity in Eastern China is slower than that in Western China and the ratio of the major axis to the minor axis of iso-seismal lines in Eastern China is smaller than that in Western China.The results also show that for a fixed magnitude the attenuation of intensity of moderate-small earthquakes is faster when intensity is higher than V and slower when intensity is lower than V-in comparison with that of moderately strong earthquakes.Furthermore,there also have been some differences in the aspects as intensity-magnitude relation between statistical laws of moderate-small earthquakes and moderately strong earthquakes.These di     

Statistical Analysis on Depth Distribution Model of Earthquake Hypocenters

In order to improve reliability of probabilistic seismic hazard analysis, shallow earthquake (depth <70 km) data, recorded with orientation precision grades 1 and 2 by modern instrument and containing depth information after 1970, are selected as statistical samples, meanwhile, North China seismic region, Central China seismic region, South China seismic region, Xinjiang seismic region and Qinghai-Xizang Plateau seismic region are chosen as statistical units to study the depth distribution characteristics of shallow earthquakes. Considering the differences of depth distribution characteristics of earthquakes with different magnitudes, the following magnitude intervals are adopted to analyze earthquakes with different magnitude scales, respectively: M S=2.0～2.9, M S=3.0～3.9, M S=4.0～4.9, M S=5.0～5.9 and M S=6.0～6.9. The results show that hypocenter depths are normally distributed by and large around the mean depth of the corresponding seismic region. The probabilistic distribution curves of earthquake depth in West China are wider than those in East China. The probabilistic distribution deviation, σ, of West China is greater than those of East China, that is, earthquakes in West China have a wider range in terms of depth. There is also a tendency that the absolute value of mean hypocenter depth increases with the magnitude by and large.     

Study on the Method for Obtaining Acceleration Waveform Records from Velocity Type Seismograms of the Digital Seismograph Network

The authors proposed a method for obtaining high-quality acceleration seismograms from velocity type seismograms of digital Seismographic network, and took as an example the analysis and processing of the seismograms of a same earthquake that was simultaneously recorded by velocity seismograph CTS1-EDAS24 and strong motion seismograph EST-Q4128 installed in Jixian Station, Tianjin. The calculation steps and the processing method have been discussed in detail. From the analysis and the comparison of the obtained results, it is concluded that the proposed method is simple and effective, and it broadens the application of digital seismographic network.     

Comparison between earthquake magnitudes determined by China seismograph network and US seismograph network (Ⅱ):Surface wave magnitude

By using orthogonal regression method, a systematic comparison is made between surface wave magnitudes determined by Institute of Geophysics of China Earthquake Administration (IGCEA) and National Earthquake Information Center of US Geological Survey (USGS/NEIC) on the basis of observation data collected by the two institutions between 1983 and 2004. A formula is obtained which reveals the relationship between surface wave magnitudes determined by China seismograph network and US seismograph network. The result shows that, as different calculation formulae and observational instruments are used, surface wave magnitude determined by IGCEA is generally greater by 0.2 than that determined by NEIC: for M=3.5～4.5 earthquakes, it is greater by 0.3;for M=5.0～6.5 earthquakes, it is greater by 0.2;and for M≥7.0 earthquakes, it is greater by no more than 0.1.     

Comparison between earthquake magnitudes determined by China seismograph network and US seismograph networks (I): Body wave magnitude

Introduction Gutenberg (1945a, b) introduced body wave magnitude based on P, PP and S waves (with a period of 0.5~12.0 s) of teleseismic events. Body wave magnitude includes mb determined with short-period seismograph and mB determined with middle- and long-period seismographs. Some-times it is written as m, which is referred to as unified earthquake magnitude. mb represents earth-quake magnitude measured with body wave amplitude around 1 s, while mB represents earthquake magnitude measured …     

Comparison between earthquake magnitudes determined by China seismograph network and US seismograph networks (Ⅰ): Body wave magnitude

By using orthogonal regression method, a systematic comparison is made between body wave magnitudes determined by Institute of Geophysics of China Earthquake Administration (IGCEA) and National Earthquake Information Center of US Geological Survey (USGS/NEIC) on the basis of observation data from China and US seismograph networks between 1983 and 2004. The result of orthogonal regression shows no systematic error between body wave magnitude mb determined by IGCEA and mb (NEIC). Provided that mb (NEIC) is taken as the benchmark, body wave magnitude determined by IGCEA is greater by 0.2～0.1 than the magnitude determined by NEIC for M=3.5～4.5 earthquakes; for M=5.0～5.5 earthquakes, there is no difference; and for M≥6.0 earthquakes, it is smaller by no more than 0.2. This is consistent with the result of comparison by IDC (International Data Center).     

The November 14, 2001 west of Kunlun Mountain Pass earthquake: An earthquake with unsaturated surface wave magnitude

Introduction According to the Rapid Earthquake Information Release of CNDSN (Department of Earth- quake Monitoring and Prediction, China Earthquake Administration, 2002), an earthquake with surface wave magnitude MS=8.1 shook west of Kunlun Mountain Pass (KMP) at the juncture of Xinjiang, Qinghai and Xizang on November 14, 2001. This is the largest and the only MS>8.0 earthquake in Chinese mainland over 50 years since the August 15, 1950 MS=8.6 (MW=8.6) Chayuearthquake in Tibeta…     

763面波震级和大震速报

大量的观测资料表明我国大震速报台网与世界台网震级存在较大的偏差，而７６３面波震级与世界台网比较一致的事实，提出了将７６３面波震级用于大震速报的建议及其可行性。     

Magnitude and distance distribution of strong aftershocks in Sichuan-Yunnan region

Using the earthquake sequences data with MS≥6.5 since 1966 in Sichuan-Yunnan region, we research the charac-teristic of the magnitude difference distribution between main shocks and their strong aftershocks; and then study the spatial distribution characteristic of the strong aftershocks away from their main shocks. The result shows that the magnitude difference distribution obeys intercepted exponential distribution, while the spatial distribution of strong aftershocks obeys normal distribution and the dominated distribution area of strong shocks is 10~39 km away from main shock. Finally the probability density function of the magnitude difference distribution and the spatial distribution of strong aftershocks is deduced.     

Study of calibration function for surface wave magnitude of DK1 seismographs

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Differences between magnitudes of Taiwan earthquakes from catalogs of Taiwan and Beijing

IntroductionTaiwanlocatedinthecollisionboundalbetweentheEurasianandthePhilippineSeaplatesisoneofhighseismicityregionsintheworld.HundredsofearthquakeswithM25occurredperyearandmorethan40withM27since1900.Amongtheseevents,shalloweventswithdepthofseveraltensofkilometersandintermediate-deepeventswithdepthof100-200kinexistwhichrepresentsacharacterofthesubductionzone.ThemagnitudesofTaiwaneventslistedinthecatalogofChineseearthquakesaretakenfromsomehistoricaldocumentsandGutenbergandRichter'sworks(19…     

Seismic characteristics near the epicenter of the 1303 Hongtong M=8 earthquake, Shanxi Province and its implication

In this paper, we calculated the seismic pattern of instrumental recorded small and moderate earthquakes near the epicenter of the 1303 Hongtong M=8 earthquake, Shanxi Province. According to the spatial distribution of small and moderate earthquakes, 6 seismic dense zones are delineated. Temporal distribution of ML≥2 earthquakes since 1970 in each seismic dense zone has been analyzed. Based on temporal distribution characteristics and historical earthquake activity, three types of seismicities are proposed. The relationship between seismic types and crustal medium is analyzed. The mechanism of three types is discussed. Finity of strong earthquake recurrence is proposed. Seismic hazard in mid-long term and diversity of earthquake disaster in Shanxi seismic belt are discussed.