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1.
Repeat times of strong shallow mainshocks have been determined by the use of instrumental and historical data for 68 seismogenic sources in the Aegean and surrounding area (34°N–43°N, 18°E–30°E). For 49 of these sources at least two interevent times (three mainshocks) are available for each source. By using the repeat times for these 49 sources the following relation has been determined: $$\log T_t = 0.36M_{\min } + 0.35M_p + a$$ whereT t is the repeat time, measured in years,M p the surface wave magnitude of the preceding mainshock,M min the magnitude of the smallest earthquake considered and “a” parameter which varies from source to source. A multilinear correlation coefficient equal to 0.89 was determined for this relation. By using the same repeat times for the 49 seismogenic sources, the following relation has been determined between the magnitude,M f , of the following mainshock andM min andM p . $$M_f = 0.95M_{\min } - 0.49M_p + m$$ wherem is a constant which varies from source to source. A multilinear correlation coefficient equal to 0.80 was found for this relation. The model expressed by these two relations is represented by a scheme of a time variation of stress under constant tectonic loading. In this scheme, the maximum stress values during the different seismic cycles fluctuate around a value, τ1, in a relatively narrow stress interval, expressing the high correlation coefficient of the relation between LogT andM p . On the contrary, the minimum stress values fluctuate around a value, τ2, in a much broader stress interval. However, each of these minimum stress values becomes lower or higher than τ2 if the previous one is higher or lower than τ2, respectively, expressing the negative correlation betweenM f andM p .  相似文献   

2.
The Aegean and surrounding area (34°N–43°N, 18°E–30°E) is separated into 76 shallow and intermediate depth seismogenic sources. For 74 of these sources intervent times for strong mainshocks have been determined by the use of instrumental and historical data. These times have been used to determine the following empirical relations: $$\begin{gathered} \log T_t = 0.24M_{\min } + 0.25M_p - 0.36\log \dot M_0 + 7.36 \hfill \\ M_f = 1.04M_{\min } - 0.31M_p + 0.28\log \dot M_0 - 4.85 \hfill \\ \end{gathered} $$ whereT 1 is the interevent time, measured in years,M min the surface wave magnitude of the smallest mainshock considered,M p the magnitude of the preceding mainshock,M f the magnitude of the following mainshock, \(\dot M_0 \) the moment rate in each source per year. A multiple correlation coefficient equal to 0.74 and a standard deviation equal to 0.18 for the first of these relations were calculated. The corresponding quantities for the second of these relations are 0.91 and 0.22. On the basis of the first of these relations and taking into consideration the time of occurence and the magnitude of the last mainshock, the probabilities for the occurrence of mainshocks in each seismogenic source of this region during the decade 1993–2002 are determined. The second of these relations has been used to estimate the magnitude of the expected mainshock.  相似文献   

3.
Investigation of the time-dependent seismicity in 274 seismogenic regions of the entire continental fracture system indicates that strong shallow earthquakes in each region exhibit short as well as intermediate term time clustering (duration extending to several years) which follow a power-law time distribution. Mainshocks, however (interevent times of the order of decades), show a quasiperiodic behaviour and follow the ‘regional time and magnitude predictable seismicity model’. This model is expressed by the following formulas $$\begin{gathered} \log T_t = 0.19 M_{\min } + 0.33 M_p - 0.39 \log m_0 + q \hfill \\ M_f = 0.73 M_{\min } - 0.28 M_p + 0.40 \log m_0 + m \hfill \\ \end{gathered} $$ which relate the interevent time,T t (in years), and the surface wave magnitude,M f , of the following mainshock: with the magnitude,M min, of the smallest mainshock considered, the magnitude,M p , of the preceded mainshock and the moment rate,m 0 (in dyn.cm.yr?1), in a seismogenic region. The values of the parametersq andm vary from area to area. The basic properties of this model are described and problems related to its physical significance are discussed. The first of these relations, in combination with the hypothesis that the ratioT/T t , whereT is the observed interevent time, follows a lognormal distribution, has been used to calculate the probability for the occurrence of the next very large mainshock (M s ≥7.0) during the decade 1993–2002 in each of the 141 seismogenic regions in which the circum-Pacific convergent belt has been separated. The second of these relations has been used to estimate the magnitude of the expected mainshock in each of the regions.  相似文献   

4.
In order to estimate the recurrence intervals for large earthquakes that occurred in the Marmara region, this region, limited with the coordinates of 39°–42°N, 25°–32°E, has been separated into seven seismogenic sources on the basis of certain seismological criteria, and regional time- and magnitude-predictable model has been applied for these sources. Considering the interevent time between successive mainshocks, the following two predictive relations were computed: log T t = 0.26 M min + 0.06 M p –0.56 log M 0 + 13.79 and M f = 0.63 M min ? 0.07 M p + 0.43 log M 0 ? 7.56. Multiple correlation coefficient and standard deviation have been computed as 0.53 and 0.35 for the first relation and 0.66 and 0.39 for the second relation, respectively. On the basis of these relations and using the occurrence time and magnitude of the last mainshocks in each seismogenic source, the probabilities of occurrence P(Δt) of the next mainshocks during the next five decades and the magnitude of the expected mainshocks were determined.  相似文献   

5.
We examined the seismic activity which preceded six strong mainshocks that occurred in the Aegean (M?=?6.4–6.9, 33–43° N, 19–28° E) and two strong mainshocks that occurred in California (M?=?6.5–7.1, 32–41° N, 115–125° W) during 1995–2010. We find that each of these eight mainshocks has been preceded by a pronounced decelerating and an equally easily identifiable accelerating seismic sequence with the time to the mainshock. The two preshock sequences of each mainshock occurred in separate space, time, and magnitude windows. In all eight cases, very low decelerating seismicity, as well as very low accelerating seismicity, is observed around the actual epicenter of the ensuing mainshock. Statistical tests on the observed measures of decelerating, q d, and accelerating, q a, seismicity against similar measures calculated using synthetic catalogs with spatiotemporal clustering based on the ETAS model show that there is an almost zero probability for each one of the two preshock sequences which preceded each of the eight mainshocks to be random. These results support the notion that every strong shallow mainshock is preceded by a decelerating and an accelerating seismic sequence with predictive properties for the ensuing mainshock.  相似文献   

6.
The various useful source-parameter relations between seismic moment and common use magnitude lg(M 0) andM s,M L,m b; between magnitudesMs andM L,M s andm b,M L andm b; and between magnitudeM s and lg(L) (fault length), lg (W) (fault width), lg(S) (fault area), lg(D) (average dislocation);M L and lg(f c) (corner frequency) have been derived from the scaling law which is based on an “average” two-dimensional faulting model of a rectangular fault. A set of source-parameters can be estimated from only one magnitude by using these relations. The average rupture velocity of the faultV r=2.65 km/s, the total time of ruptureT(s)=0.35L (km) and the average dislocation slip rateD=11.4 m/s are also obtained. There are four strong points to measure earthquake size with the seismic moment magnitudeM w.
  1. The seismic moment magnitude shows the strain and rupture size. It is the best scale for the measurement of earthquake size.
  2. It is a quantity of absolute mechanics, and has clear physical meaning. Any size of earthquake can be measured. There is no saturation. It can be used to quantify both shallow and deep earthquakes on the basis of the waves radiated.
  3. It can link up the previous magnitude scales.
  4. It is a uniform scale of measurement of earthquake size. It is suitable for statistics covering a broad range of magnitudes. So the seismic moment magnitude is a promising magnitude and worth popularization.
  相似文献   

7.
In order to estimate the recurrence intervals for large earthquakes occurring in eastern Anatolia, this region enclosed within the coordinates of 36∘–42∘N, 35∘–45∘E has been separated into nine seismogenic sources on the basis of certain seismological and geomorphological criteria, and a regional time- and magnitude-predictable model has been applied for these sources. This model implies that the magnitude of the preceding main shock which is the largest earthquake during a seismic excitation in a seismogenic source governs the time of occurrence and the magnitude of the expected main shock in this source. The data belonging to both the instrumental period (MS≥ 5.5) until 2003 and the historical period (I0≥ 9.0 corresponding to MS≥ 7.0) before 1900 have been used in the analysis. The interevent time between successive main shocks with magnitude equal to or larger than a certain minimum magnitude threshold were considered in each of the nine source regions within the study area. These interevent times as well as the magnitudes of the main shocks have been used to determine the following relations:
fwawhere Tt is the interevent time measured in years, Mmin is the surface wave magnitude of the smallest main shock considered, Mp is the magnitude of the preceding main shock, Mf is magnitude of the following main shock, and M0 is the released seismic moment per year in each source. Multiple correlation coefficient and standard deviation have been computed as 0.50 and 0.28, respectively for the first relation. The corresponding values for the second relation are 0.64 and 0.32, respectively. It was found that the magnitude of the following main shock Mf does not depend on the preceding interevent time Tt. This case is an interesting property for earthquake prediction since it provides the ability to predict the time of occurrence of the next strong earthquake. On the other hand, a strong negative dependence of Mf on Mp was found. This result indicates that a large main shock is followed by a smaller magnitude one and vice versa. On the basis of the first one of the relations above and taking into account the occurrence time and magnitude of the last main shock, the probabilities of occurrence P(Δ t) of main shocks in each seismogenic source of the east Anatolia during the next 10, 20, 30, 40 and 50 years for earthquakes with magnitudes equal 6.0 and 7.0 were determined. The second of these relations has been used to estimate the magnitude of the expected main shock. According to the time- and magnitude-predictable model, it is expected that a strong and a large earthquake can occur in seismogenic Source 2 (Erzincan) with the highest probabilities of P10 = 66% (Mf = 6.9 and Tt = 12 years) and P10 = 44% (Mf = 7.3 and Tt = 24 years) during the future decade, respectively.  相似文献   

8.
The occurrence of the September 28, 2004 M w = 6.0 mainshock at Parkfield, California, has significantly increased the mean and aperiodicity of the series of time intervals between mainshocks in this segment of the San Andreas fault. We use five different statistical distributions as renewal models to fit this new series and to estimate the time-dependent probability of the next Parkfield mainshock. Three of these distributions (lognormal, gamma and Weibull) are frequently used in reliability and time-to-failure problems. The other two come from physically-based models of earthquake recurrence (the Brownian Passage Time Model and the Minimalist Model). The differences resulting from these five renewal models are emphasized.  相似文献   

9.
The evolution laws of LURR (Loading–Unloading Response Ratio) before strong earthquakes, especially the peak point of LURR, are described in this paper. The results of four methods (experimental, numerical simulation, seismic data analysis and with damage mechanics analysis) lead to a consistent conclusion—the evolution laws of LURR before strong earthquakes are that, at the early stage of the seismic cycle, LURR will fluctuate around 1 and in the late stage, it rises swiftly and to its peak point. At some time after this peak point, a catastrophic event or events occur. These do not occur at the peak point, but lag behind. The lag time which is denoted by T 2 depends on the magnitude M of the upcoming earthquake among other factors. In order to consider the influence of geophysical parameters in a specific region such as $ \dot{\gamma }, $ E a and J (t), where $ \dot{\gamma } $ is the shear strain rate of tectonic loading in situ, E a is the sum of radiated energy of all earthquake occurring in a specific region measured during a long time duration (110 years in this paper) divided by the area of the region and the time duration, and J (t) is a parameter denoting the LURR anomaly area weighted with Y (the value of LURR) and represents the expanse and degree of the seismogenic zone. The dimensional analysis method has been used to reveal the relation between M, T 2 and other parameters in situ for more reliable earthquake prediction.  相似文献   

10.
In this work we review earthquakes that happened in Southern Siberia and Mongolia within the coordinates of 42°–62° N and 80°–124° E and first propose relationships between earthquake parameters (a surface-wave earthquake magnitude M s and an epicentral intensity(I 0) based on the MSK-64 scale) and maximal distances from an earthquake epicenter (R e max), hypocenter (R h max), and a seismogenic fault (R f max) to the localities of secondary coseismic effects. Special attention was paid to the study of these relationships for the effects of soil liquefaction. Hence, it was shown that secondary deformations from an earthquake were distributed in space away from an earthquake epicenter, than from an associating seismogenic fault. The effects of soil liquefaction are manifested by several times closer to a seismogenic fault, than all other effects, regardless of the type of tectonic movement in a seismic focus. Within the 40 km zone from an earthquake epicenter 44% of the known manifestations of liquefaction process occurred; within the 40 km zone from a seismogenic fault—90%. We propose the next relationship for effects of soil liquefaction: M s = 0.007 × R e max + 5.168 that increases the limits of the maximum epicentral distance at an earthquake magnitude of 5.2 ≤ M s ≤ 8.1 as compared to the corresponding relationships for different regions of the world.  相似文献   

11.
The July 2019 MW6.4 Ridgecrest, California earthquake and its distinct foreshocks were well recorded by local and regional stations, providing a great opportunity to characterize its foreshocks and investigate the nucleation mechanisms of the mainshock. In this study, we utilized the match-and-locate (M&L) method to build a high-precision foreshock catalog for this MW6.4 earthquake. Compared with the sequential location methods (matched-filter + cross-correlation-based hypoDD), our new catalog contains more events with higher location accuracy. The MW6.4 mainshock was preceded by 40 foreshocks within ～2 h (on July 4, 2019 from 15:35:29 to 17:32:52, UTC). Their spatiotemporal distribution revealed a complex seismogenic structure consisting of multiple fault strands, which were connected as a throughgoing fault by later foreshocks and eventually accommodated the 2019 MW6.4 mainshock. To better understand the nucleation mechanism, we determined the rupture dimension of the largest ML4.0 foreshock by calculating its initial rupture and centroid points using the M&L method. By estimating Coulomb stress change we suggested that the majority of foreshocks following the ML4.0 event and MW6.4 mainshock occurred within regions of increasing Coulomb stress, indicating that they were triggered by stress transfer. The nucleation process before the ML4.0 event remains unclear due to the insufficient sampling rate of waveforms and small magnitude of events. Thus, our study demonstrates that the M&L method has superior detection and location ability, showing potential for studies that require high-precision location (e.g., earthquake nucleation).  相似文献   

12.
The “earthquake nucleation” is discussed in this paper. The acceleration is a property of the nucleation phase and is a necessary condition of earthquake instability too. If the acceleration property of this nucleating process is described by the equation dΘ/dt=C/(t f?t) n , the process can be summarized briefly that the rate of cumulative seismic release is proportional to the inverse power of the remaining time to failure. Based on this principle, the foreshock sequence of the 1975 Haicheng earthquake withM S7.3, was analysed backward. It is stated clearly that the time-to-failure and magnitude of the mainshock can be predicted successfully if the coefficientr 2 attains to the maximum. In the estimation of mainshock time, the error can generally be less than, or far less than, one-half the remaining time between the time of the last used data point and the mainshock.  相似文献   

13.
According to the China Earthquake Networks Center, a strong earthquake of M6.8 occurred in Luding County, Ganzi Tibetan Autonomous Prefecture, Sichuan Province, China (102.08°E, 29.59°N), on September 5, 2022, with a focal depth of 16 km. Rapid determination of the source parameters of the earthquake sequence is vital for post-earthquake rescue, disaster assessment, and scientific research. Near-field seismic observations play a key role in the fast and reliable determination of earthquake source parameters. The numerous broadband seismic stations and strong-motion stations recently deployed by the National Earthquake Intensity Rapid Report and Early Warning project have provided valuable real-time near-field observation data. Using these near-field observations and conventional mid- and far-field seismic waveform records, we obtained the focal mechanism solutions of the mainshock and M ≥ 3.0 aftershocks through the waveform fitting method. We were further able to rapidly invert the rupture process of the mainshock. Based on the evaluation of the focal mechanism solution of the mainshock and the regional tectonic setting, we speculate that the Xianshuihe fault formed the seismogenic structure of the M6.8 strong earthquake. The aftershocks formed three spatially separated clusters with distinctly different focal mechanisms, reflecting the segmented nature of the Xianshuihe fault. As more high-frequency information has been applied in this study, the absolute location of the fault rupture is better constrained by the near-field strong-motion data. The rupture process of the mainshock correlates well with the spatial distribution of aftershocks, i.e., aftershock activities were relatively weak in the maximum slip area, and strong aftershock activities were distributed in the peripheral regions.  相似文献   

14.
Tsunamis are most destructive at near to regional distances, arriving within 20–30 min after a causative earthquake; effective early warning at these distances requires notification within 15 min or less. The size and impact of a tsunami also depend on sea floor displacement, which is related to the length, L, width, W, mean slip, D, and depth, z, of the earthquake rupture. Currently, the primary seismic discriminant for tsunami potential is the centroid-moment tensor magnitude, M w CMT , representing the product LWD and estimated via an indirect inversion procedure. However, the obtained M w CMT and the implied LWD value vary with rupture depth, earth model, and other factors, and are only available 20–30 min or more after an earthquake. The use of more direct discriminants for tsunami potential could avoid these problems and aid in effective early warning, especially for near to regional distances. Previously, we presented a direct procedure for rapid assessment of earthquake tsunami potential using two, simple measurements on P-wave seismograms—the predominant period on velocity records, T d , and the likelihood, T 50 Ex , that the high-frequency, apparent rupture-duration, T 0, exceeds 50–55 s. We have shown that T d and T 0 are related to the critical rupture parameters L, W, D, and z, and that either of the period–duration products T d T 0 or T d T 50 Ex gives more information on tsunami impact and size than M w CMT , M wp, and other currently used discriminants. These results imply that tsunami potential is not directly related to the product LWD from the “seismic” faulting model, as is assumed with the use of the M w CMT discriminant. Instead, information on rupture length, L, and depth, z, as provided by T d T 0 or T d T 50 Ex , can constrain well the tsunami potential of an earthquake. We introduce here special treatment of the signal around the S arrival at close stations, a modified, real-time, M wpd(RT) magnitude, and other procedures to enable early estimation of event parameters and tsunami discriminants. We show that with real-time data currently available in most regions of tsunami hazard, event locations, m b and M wp magnitudes, and the direct, period–duration discriminant, T d T 50 Ex can be determined within 5 min after an earthquake occurs, and T 0, T d T 0, and M wpd(RT) within approximately 10 min. This processing is implemented and running continuously in real-time within the Early-est earthquake monitor at INGV-Rome (http://early-est.rm.ingv.it). We also show that the difference m b  ? log10(T d T 0) forms a rapid discriminant for slow, tsunami earthquakes. The rapid availability of these measurements can aid in faster and more reliable tsunami early warning for near to regional distances.  相似文献   

15.
In October and November 2002, the Molise region (southern Italy) was struck by two moderate magnitude earthquakes within 24 hours followed by an one month long aftershocks sequence. Soon after the first mainshock (October 31st, 10.32 UTC, Mw 5.7), we deployed a temporary network of 35 three-component seismic stations. At the time of occurrence of the second main event (November 1st, 15.08 UTC, Mw 5.7) the eight local stations already installed allowed us to well constrain the hypocentral parameters. We present the location of the two mainshocks and 1929 aftershocks with 2 < ML < 4.2. Earthquake distribution reveals a E-trending 15 km long fault system composed by two main segments ruptured by the two mainshocks. Aftershocks define two sub-vertical dextral strike-slip fault segments in agreement with the mainshock fault plane solutions. P- and T-axes retrieved from 170 aftershocks focal mechanisms show a coherent kinematics: with a sub-horizontal NW and NE-trending P and T-axes, respectively. For a small percentage of focal mechanisms (∼ 10%) a rotation of T axes is observed, resulting in thrust solutions. The Apenninic active normal fault belt is located about 80 km westward of the 2002 epicentral area and significant seismicity occurs only 20-50 km to the east, in the Gargano promontory. Seismic hazard was thought to be small for this region because neither historical earthquake are reported in the Italian seismic catalogue or active faults were previously identified. In this context, the 2002 seismic sequence highlights the existence of trans-pressional active tectonics in between the extensional Apenninic belt and the Apulian foreland.  相似文献   

16.
The 2022 MS 6.8 Luding earthquake is the strongest earthquake in Sichuan Province, Western China, since the 2017 MS 7.0 Jiuzhaigou earthquake. It occurred on the Moxi fault in the southeastern segment of the Xianshuihe fault, a tectonically active and mountainous region with severe secondary earthquake disasters. To better understand the seismogenic mechanism and provide scientific support for future hazard mitigation, we summarize the preliminary results of the Luding earthquake, including seismotectonic background, seismicity and mainshock source characteristics and aftershock properties, and direct and secondary damage associated with the mainshock. The peak ground displacements in the NS and EW directions observed by the nearest GNSS station SCCM are ～35 mm and ～55 mm, respectively, resulting in the maximum coseismic dislocation of 20 mm along the NWW direction, which is consistent with the sinistral slip on the Xianshuihe fault. Back-projection of teleseismic P waves suggest that the mainshock rupture propagated toward south-southeast. The seismic intensity of the mainshock estimated from the back-projection results indicates a Mercalli scale of VIII or above near the ruptured area, consistent with the results from instrumental measurements and field surveys. Numerous aftershocks were reported, with the largest being MS 4.5. Aftershock locations (up to September 18, 2022) exhibit 3 clusters spanning an area of 100 km long and 30 km wide. The magnitude and rate of aftershocks decreased as expected, and the depths became shallower with time. The mainshock and two aftershocks show left-lateral strike-slip focal mechanisms. For the aftershock sequence, the b-value from the Gutenberg-Richter frequency-magnitude relationship, h-value, and p-value for Omori’s law for aftershock decay are 0.81, 1.4, and 1.21, respectively, indicating that this is a typical mainshock-aftershock sequence. The low b-value implies high background stress in the hypocenter region. Analysis from remote sensing satellite images and UAV data shows that the distribution of earthquake-triggered landslides was consistent with the aftershock area. Numerous small-size landslides with limited volumes were revealed, which damaged or buried the roads and severely hindered the rescue process.  相似文献   

17.
2021年8月26日甘肃省酒泉市阿克塞县发生M5.5地震,这次地震是发生在祁连山地震构造带西段的一次显著地震。利用区域台网记录的宽频带地震波形数据,通过CAP方法反演阿克塞M5.5主震及其M3.7余震的震源机制解,进一步利用双差定位方法对研究区2021年1月1日—11月29日间的地震事件进行重定位,以此分析此次地震的发震构造及其意义。结果表明阿克塞M5.5地震是一次以逆冲性质为主的地震事件;重定位后,地震事件呈明显的集中分布特征,阿克塞M5.5主震震源深度为14.1 km,余震序列震源深度大多分布于15～25 km。综合分析震源机制解、重定位结果以及区域构造背景,认为阿克塞地震的发震断层为党河南山南缘断裂,未来应重点关注祁连山西段发生中强地震的危险。  相似文献   

18.
于书媛  方良好  宴金旭  倪红玉  陈靓  丁娟 《地震工程学报》2022,44(6):1469-1477,1488
运用升、降轨Sentinel-1A 卫星的差分干涉影像,获取2019-06-17四川宜宾长宁 MS6．0地震的三维同震形变场.在此基础上,以升降轨同震形变数据为约束条件,基于 Okada弹性半空间位错模型反演得到发震断层符合走滑和逆冲特征,断层破裂尺度约为15km×20km,断层滑动角为 44．37°,断层倾角为56．42°,震源深度约为10．2km,矩震级为 M W5．8.最后,采用SBAS-InSAR 技术获取该地区2019-04-05至2019-08-03各时间段的累计形变,结果认为该区域在震前近场形变波动较小,震后一段时间累积形变增长,分析原因可能是余震分布使得地表变化处于不稳定状态.通过与已有研究文献的比较和对该区域断层构造的分析,推测此次长宁地震发震断层由反演出的断层滑动引起,滑动面上缘接近地表,主震引起的次级断层活动触发短期内强余震频发.  相似文献   

19.
Based on the seismic phase reports of the Yangbi area from January 1 to June 25, 2021, and the waveform data of M ≥ 4 earthquakes, we obtained the relocation results and focal mechanism solutions of the MS6.4 Yangbi earthquake sequence using the HypoDD and CAP methods. Based on our results, our main conclusions are as follows: (1) the MS6.4 Yangbi earthquake sequence is a typical foreshock-mainshock-aftershock sequence. The foreshocks of the first two stages have the obvious fronts of migration and their migration rate increased gradually. There was no apparent front of migration during the third stage, and the occurrence of the mainshock was related to stress triggering from a M5.3 foreshock. We tentatively speculate that the rupture pattern of the Yangbi earthquake sequence conforms to the cascading-rupture model; and (2) the main fault of the MS6.4 Yangbi earthquake sequence is a NW-trending right-lateral strike-slip fault. As time progressed, a minor conjugate aftershock belt formed at the northwest end of this fault, and a dendritic branching structure emerged in the southern fault segment, showing a complex seismogenic fault structure. We suggested that the fault of the Yangbi earthquake sequence may be a young sub-fault of the Weixi-Weishan fault.  相似文献   

20.
Detecting tempo-spatial changes of crust stress associated with major earthquakes has implications for understanding earthquake seismogenic processes. We conducted a joint analysis of b-value and apparent stress in the source region before the March 11, 2011 MW9.0 Tohoku-Oki, Japan earthquake. Earthquakes that occurred between January 1, 2000 and March 8, 2011 were used to estimate b-values, while source parameters of events with magnitudes of Ms5.0–6.9 between January 1, 1997 and March 8, 2011 were used to calculate the apparent stresses. Our results show that the average b-value decreased steadily from 1.26 in 2003 to 0.99 before the Tohoku-Oki mainshock. This b-value decrease coincided with an increase in the apparent stress from 0.65 MPa to 1.64 MPa. Our results reveal a clear negative correlation between the decrease in b-value and increase in apparent stress, which lasted for approximately eight years prior to the 2011 mainshock. Additionally, spatial pattern results of the relative change in b-value show that the area associated with drastic b-value decreases (25% or greater) was concentrated near the 2011 mainshock epicenter. The joint analysis of b-value and apparent stress provides a promising method for detecting anomalies that could serve as potential indicators of large earthquakes.  相似文献   

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