Temporal Variations Of B-value Research Articles

An evaluation of the characteristic aftershock parameters following the 24 January 2020 Mw = 6.8 Elazığ-Sivrice (Türkiye) earthquake

A comprehensive evaluation of region-time-magnitude behaviours of aftershocks following the 24 January 2020 (Mw = 6.8) Elazığ-Sivrice (Türkiye) earthquake was achieved by using the characteristic parameters such as b-value, p-value, Dc-value and Mamax value of aftershock occurrences. The b-value was calculated as 0.82 ± 0.02 by considering the magnitude of the completeness value as Mcomp = 1.9, and it is relatively small compared to typical b ≈ 1 for the magnitude-frequency relationship of aftershocks. This low b-value may also be caused by the abundance of aftershocks with ML ≥ 4.0. The p-value was computed as 0.80 ± 0.02 with c-value = 0.279 ± 0.098 and is smaller than the global value of p ≈ 1. This low p-value may be due to a relatively slow decay rate of aftershock activity, and the modified Omori model seems appropriate for the estimation of decay parameters. The Dc-value was estimated as 1.87 ± 0.07. This large value shows that aftershocks are homogeneously distributed and more clustered at larger scales/in smaller areas. The temporal variation of b-value indicates that decreases in b-value may result from the gradual increase in the effective stress following the larger aftershocks. The lowest b-values and Mamax values greater than 5.0 were observed in the north, south and southwest parts of the mainshock including Pütürge and Erkenek segments. These results show that there is an apparent relation between the smallest b-values and the largest Mamax values. The largest p-values were estimated in and around the main shock including Pütürge segment. The regions with the smallest b-value and the largest p-value have high stress and coseismic deformation, respectively. Stress variations and coseismic deformation are extremely effective on the changes of b- and p-values. As a remarkable result, aftershock hazard following the mainshock may be considered extremely related to aftershock parameters, and detailed analyses of the region-time-magnitude characteristics of aftershocks are recommended for a preliminary evaluation following the mainshock.

Spatial and temporal variation of b-value at Cerro Machín volcano, Colombia

Se llevó a cabo un estudio de la variación espacio-temporal del valor b de la relación frecuencia-magnitud de sismos ocurridos en el Volcán Cerro Machín (VCM), Colombia, para el período 2007-2020. Se pudo establecer que el valor b presenta variaciones espaciales caracterizadas por valores altos (1,1-1,3) en la parte superficial del volcán, debajo del domo principal y hasta una profundidad de 1 km. Entre 1 y 6 km de profundidad, se observaron valores normales a bajos (0,8-0,6). Bajo el domo Tapias, entre 8 y 13 km de profundidad, se observaron valores altos de b (1,1-1,3). Estos valores anómalos indicarían zonas de circulación de fluidos hidrotermales en la parte superficial y posibles reservorios de magma en la parte más profunda del VCM. Adicionalmente, se observaron variaciones temporales del valor b; se destacan tres cambios importantes, relacionados con variaciones en la actividad del VCM: el primero, ocurrido en noviembre 2008, se asoció con un enjambre al NE y E del domo principal (3-5 km de profundidad); el segundo, ocurrido en agosto-diciembre 2010, se asoció con la presencia de sismicidad profunda (12-18 km) a unos 8 km al SE del domo principal, y el tercero, ocurrido en febrero de 2018, se asoció con un enjambre sísmico (3-5 km de profundidad) al SW del domo principal. Estos tres cambios se interpretan como posibles intrusiones de pulsos de magma, asociadas a un dique o silo superficial (<4 km de profundidad) y a una entrada de magma a mayores profundidades (>15 km). Algunos de estos cambios en el valor b estuvieron asociados con cambios geoquímicos o de deformación de la superficie. Los resultados de este estudio muestran que el cálculo rutinario del valor-b sirve como herramienta de monitoreo volcánico para el VCM.

Estimation of B-Value Variation as Earthquake Precursor in Java Region with Maximum Likelihood Method

Java Island is one of the areas with a population density of 1,171 people/km2, which is relatively high compared to other regions in Indonesia. The tectonic setting of the Java region is affected by the interaction of tectonic plate subduction between the Indo-Australian Plate and the Eurasian Plate which moves at the rate of 67 mm/year. In addition, the presence of several active faults on Java Island also contributes to the tectonic setting. The implication of this setting is a relatively high level of potential earthquake events and some of them are destructive earthquakes. The estimation of b-value variations by using Gutenberg-Richter Equation plays an important role in estimating the occurrence of earthquakes. The aims of this study are to determine the role of spatial and temporal variations of b-value as earthquake precursors on Java Island. In this research, earthquakes analysis was carried out in the form of spatial and temporal variations of b-value from earthquake catalog data in 1900-2016 for the Java Island region. Based on the estimation of earthquake recurrence time for magnitude 6.5, 7, and 7.5, and also the analysis of spatial variation of b-value shows the areas with the potential for significant earthquakes in the west and eastern part of Java region. In addition, our result also obtains the existence of a seismic gap zone in the southern part of Central Java.

Pattern Recognition on Seismic Data for EarthquakePrediction Purpose

Earthquakes has been known as a destructive natural disaster. Due to high human casualties and economical losses, earthquake prediction appears critical. The b-value of Gutenberg Richter law has been considered as precursor to earthquake prediction. Temporal variation of b-value before earthquakes equal or greater than Mw = 6.0 has been examined in the south of Iran, the Qeshm island and around of this from 1995 to 2012. Clustering method by the k-means algorithm has been performed to find pattern of variation of b-value. Three clusters are obtained as optimum number of clusters by the Silhouette Index. Before all mentioned earthquakes greater than Mw = 6.0, cluster 1, which is known as a decrease in b-value has been seen. so decreasing b-value before main shocks as distinctive pattern has been considered. Also an approximate time of decrease has been determined.

Estimation of seismic hazard around the Ordos Block of China based on spatial and temporal variations of b-values

Ruinous earthquakes have frequently occurred on the border of the Ordos Block, historically. Thus, where is a future disastrous earthquake around the Ordos? This problem is becoming more and more urgent both in the scientific community and the public, particularly after the 2008 Wenchuan earthquake (Ms = 8.0). To this end, we at first compute b-values in and around the Ordos Block based on the updated catalogue with earthquakes (M ≥ 0.0) from 1 January 2010 to 31 December 2020, and presented the spatial distribution of b-values. By examining the distribution feature of b-values, we chose 14 locations on the border of the Ordos Block where the b-value is relatively low and neo-tectonic faults are active. After that, we calculate the temporal variations of b-values in these 14 places, respectively. Comparing the 14 curves of b-variations with seismic precursors on b-values, we found that four of fourteen b-variations have characteristics of earthquake precursors. Therefore, these four places, located in the western end of the Weihe Graben, both the eastern and western ends of Hetao Graben, and the northeastern front of the Tibet, are considered to be seismically dangerous in the future. Naturally, the seismic damage in these areas is more serious than other places. Hence, the study is helpful in earthquake prediction and also can provide important clues for earthquake hazard assessment around the Ordos Block.

Statistical Properties of Aftershocks for Ahar-Varzeghan Twin Earthquakes on 11 August 2012, NW Iran, and Investigation of Seismicity of North Tabriz Fault

Two earthquakes occurred on 11 August 2012 in East Azerbaijan province, NW Iran with Mw 6.3 at 12:23:15.9 and Mw 6.1; 11 minutes after the first shock at 12:34:34.8 GMT time. In this study, we concentrated on the properties of the aftershock sequences in a duration of 7.5-month time-period data after the main shocks, recorded by Broadband Iranian Network (BIN). We obtained p, c and K parameters with the maximum likelihood method and the occurrence rate was modeled by the modified Omori formula. Besides, we showed that aftershocks of the aftershock in 7 Nov. 2012 (M = 5.6) also decay according to the modified Omori law. We investigated the spatial and temporal variations of b-values before and after the twin earthquakes with Mw 6.3 and Mw 6.1 approximately 20 km around North Tabriz Fault (NTF) in the region from 1996 to 2013 using Iranian Seismological Center (IRSC). We believed that a research of the past 17 years has clearly established that spatial b-value changes and seismicity rate are highly significant and meaningful. Moreover, our research led to a warning for a probable strong motion along NTF for the coming couple of years.

Spatio-temporal evolution of frequency-magnitude distribution and seismogenic index during initiation of induced seismicity at Guy-Greenbrier, Arkansas

In this study, we carry out detailed analyses of the spatio-temporal variations of seismic b-value during the onset of the potentially induced-earthquake sequence between Guy and Greenbrier, Arkansas, to investigate correlations with pore-pressure change. The range of b-values suggests that the seismicity in the Guy-Greenbrier area is mostly a result of the activation of pre-existing faults. The spatial distribution of b-value correlates with modeled pore-pressure changes. In the northern segment of the fault, b-value increases with depth due to large pore-pressure changes and opening of new fractures in the deeper part and stress relaxation in the shallower parts. Whereas, in the southern segment, the shallower part shows higher b-values due to higher pore-pressure fluctuations but the deeper part in the crystalline basement has low b-value due to higher confining stress. The correlation between the temporal variation of b-value and hypocentral depth explains a previously observed temporal drop of b-value. This suggests that temporal variations should be interpreted along with the spatial variations. Estimation of the seismogenic indices for the Guy-Greenbrier fault is provided. Our analysis suggests that monitoring changes in b-value and seismogenic indices during an injection period might be used to avoid the occurrence of significant events if injection volume is reduced at critical times.

Space-time assessing of the earthquake potential in recent years in the Eastern Anatolia region of Turkey

In this study, a statistical analysis is carried out to reveal the current earthquake potential in the Eastern Anatolia region of Turkey. For this purpose, a space-time assessing based on the recent changes in Gutenberg-Richter b-value, seismic quiescence Z-value, cumulative moment, annual probability and recurrence time of earthquakes is achieved. Temporal variation of b-value indicates that average b-value decreased from 1.25±0.02 between 2002 and 2010 to 1.08±0.02 between 2011 and 2015. A clear quiescence in the seismic moment in recent years may be a clue foretelling the occurrence of an intense event. Annual probability of the earthquakes between 3.5 and 4.0 magnitude levels exhibits a value equal to and larger than 30. Recurrence time of the earthquakes has a value between 2.0 and 3.0 years for magnitude level of 6.0, and a value between 6.0 and 7.0 years for magnitude level of 7.0. A significant decrease in b-value and clear quiescence anomalies in Z-value at the beginning of 2015 are observed in the several same regions. These areas cover the Central Anatolia Fault Zone, Malatya and Ovacık faults, the southeastern part of the Eastern Anatolia Fault Zone, and the junction of the Eastern Anatolia and Dead Sea Fault Zones. In these anomaly regions, a decreasing trend in b-value may be an indicator of stress increases and an increasing trend in Z-value may show the quiescence areas before the next earthquake occurrences. As a remarkable fact, these areas in the Eastern Anatolia region may be interpreted as one of the most likely locations for the major earthquakes in the future.

Statistical analysis of aftershock sequences related with two major Nepal earthquakes: April 25, 2015, MW 7.8, and May 12, 2015, MW 7.2

Present study describes the statistical properties of aftershock sequences related with two major Nepal earthquakes (April 25, 2015, MW 7.8, and May 12, 2015, MW 7.2) and their correlations with the tectonics of Nepal Himalaya. The established empirical scaling laws such as the Gutenberg–Richter (GR) relation, the modified Omori law, and the fractal dimension for both the aftershock sequences of Nepal earthquakes have been investigated to assess the spatio-temporal characteristics of these sequences. For this purpose, the homogenized earthquake catalog in moment magnitude, MW is compiled from International Seismological Center (ISC) and Global Centroid Moment Tensor (GCMT) databases during the period from April 25 to October 31, 2015. The magnitude of completeness, MC, a and b-values of Gutenberg–Richter relationship for the first aftershock sequence are found to be 3.0, 4.74, 0.75 (±0.03) respectively whereas the MC, a and b-values of the same relationship for the second aftershock sequence are calculated to be 3.3, 5.46, 0.90 (±0.04) respectively. The observed low b-values for both the sequences, as compared to the global mean of 1.0 indicate the presence of high differential stress accumulations within the fractured rock mass of Nepal Himalaya. The calculated p-values of 1.01 ± 0.05 and 0.95 ± 0.04 respectively for both the aftershock sequences also imply that the aftershock sequence of first main-shock exhibits relatively faster temporal decay pattern than the aftershock sequence of second main-shock. The fractal dimensions, DC values of 1.84 ± 0.05 and 1.91 ± 0.05 respectively for both the aftershock sequences of Nepal earthquakes also reveal the clustering pattern of earthquakes and signifies that the aftershocks are scattered all around the two dimensional space of fractured fault systems of the Nepal region. The low b-value and low DC observed in the temporal variations of b-value and DC before the investigated earthquake (MW 7.2) suggest the presence of high-stress concentrations in the thrusting regimes of the Nepal region before the failure of faults. Moreover, the decrease of b-value with the corresponding decrease of DC observed in their temporal variations can primarily act as an indicator for possible prediction of major earthquakes in the study region.

Precursor times of abnormal b-values prior to mainshocks

Seismic observations exhibit the presence of abnormal b-values prior to numerous earthquakes. The time interval from the appearance of abnormal b-values to the occurrence of mainshock is called the precursor time. There are two kinds of precursor times in use: the first one denoted by T is the time interval from the moment when the b-value starts to increase from the normal one to the abnormal one to the occurrence time of the forthcoming mainshock, and the second one denoted by T p is the time interval from the moment when the abnormal b-value reaches the peak one to the occurrence time of the forthcoming mainshock. Let T* be the waiting time from the moment when the abnormal b-value returned to the normal one to the occurrence time of the forthcoming mainshock. The precursor time, T (usually in days), has been found to be related to the magnitude, M, of the mainshock expected in a linear form as log(T) = q + rM where q and r are the coefficient and slope, respectively. In this study, the values of T, T p , and T* of 45 earthquakes with 3 ≤ M ≤ 9 occurred in various tectonic regions are compiled from or measured from the temporal variations in b-values given in numerous source materials. The relationships of T and T p , respectively, versus M are inferred from compiled data. The difference between the values of T and T p decreases with increasing M. In addition, the plots of T*/T versus M, T* versus T, and T* versus T-T* will be made and related equations between two quantities will be inferred from given data.

Tohoku rupture reloaded?

correspondence Tohoku rupture reloaded? To the Editor — Tormann et al. 1 evaluate changes in the b-value, a measure of the relative abundance of small and large earthquakes, as a function of space and time in northeast Japan. Near the high-slip zone of the 2011 magnitude 9 Tohoku-oki rupture, they document a sudden increase in the b-value at the time of the earthquake and its return to about 77% of its average 1998–2003 value within about two years. Assuming that the b-value is negatively correlated with differential stress 2 , they infer that the stress relieved by the earthquake has very rapidly recovered to levels found before the earthquake. Consequently, the authors propose that megathrust earthquake occurrences follow a Poisson process and are effectively random in time. However, we argue that the hazard of a great tsunami-producing earthquake in this section of the Japan megathrust zone is unlikely to already be almost as high as it was just before the 2011 event. Instead, many centuries of stress accumulation are required to rebuild stress and produce another great event. Prior to the earthquake, the seismicity in northeast Japan was predominantly contractional and involved reverse faults (Fig. 1a,c). Since the Tohoku-oki earthquake, there have been few reverse events near the high-slip zone of the rupture (Fig. 1b,d) and aftershocks primarily occurred as extensional (normal faulting) events in both the overriding and down- going plates of the subduction zone. The dominance of normal faulting suggests that the stress drop during the mainshock was large enough, relative to the background stress, to reverse the style of faulting near the high-slip zone 3,4 . Because events with different faulting types in northeast Japan have different b-values (Supplementary Information), we suggest that the observed coseismic rise and postseismic decay of b-values (Fig. 1f) partly reflect the fact that Tormann and colleagues sampled event populations with different mechanisms and from different source volumes in the subduction zone (Fig. 1e). Tormann and colleagues argue that reloading of stress caused by rapid postseismic deformation processes, complemented by fault healing processes and stress-field homogenization, may quickly re-establish compressional stress levels to those found just before the earthquake. However, although reloading of a megathrust rupture is indeed most rapid during the early period of postseismic relaxation, our models of stress recovery constrained by geodetic and seismicity data suggest that only a very small fraction of the approximately 10 MPa coseismic stress drop in the high-slip zone could have been recovered in the first three postseismic years. Even when considering the contributions from multiple sources of postseismic deformation 5 , the average shear-stress changes near the high-slip zone only amount to less than 0.5 MPa within three years and approach 1 MPa after relaxation of coseismic stress perturbations more than two decades later (Fig. 1g). Completion of the transient relaxation together with loading from steady plate convergence allow for full shear-stress recovery within several hundred years (Supplementary Information). In summary, we suggest that the temporal changes of b-values near the high- slip zone of the Tohoku-oki earthquake may reflect sampling of earthquakes from different volumes and fault populations in the subduction zone. Furthermore, postseismic relaxation processes are not capable of rapidly reloading the fault. Although the spatial and temporal variations of b-values are intriguing, it appears premature to assume b-values as a direct proxy for stress on the Japan subduction thrust and to argue for general randomness of megathrust earthquakes based on this observation.

Spatial and Temporal Variation of b-Values in Southwest China

In our study, we used an improved Bayesian method based on a basis spline (B-spline) function to estimate the spatial and temporal variations of b-values in Southwest China. We propose that b-values combined with seismicity and tectonic background can provide a fairly clear stress condition and can be used in earthquake hazard analysis. Very low b-values in Southwest China appear to be related to the 2008 $$M_s\,8.0$$ Wenchuan earthquake. We also suggest that the decreasing b-value trend in the Longmen Shan area from 2000 to 2008 may be an indicator of the 2008 $$M_s\,8.0$$ Wenchuan earthquake.

A review of b-value imaging and fractal dimension studies in the Andaman Sumatra subduction

The Andaman–Sumatra is one of the seismically active subduction zones and experienced three largest earthquakes in the recent past and rupturing more than 1,600-km-long portion of the plate boundary. The seismicity analysis of these large earthquakes source region (5°S–15°N latitude and 90°E–103°E longitude) has been carried out by several researchers and quantified the spatial and temporal variation of b-value which is a proxy to differential stress conditions and fractal dimension which is an indicator of material heterogeneity and strength. The results of all these studies clearly bring out the low b-value and low fractal dimension corresponding to locales were sizable magnitude earthquakes have occurred. Further locales of high stress regions are identified.

Low b-value prior to the Indo-Myanmar subduction zone earthquakes and precursory swarm before the May 1995 M 6.3 earthquake

Some 455 events (mb⩾4.5) in the Indo-Myanmar subduction zone are compiled using the ISC/EHB/NEIC catalogues (1964–2011) for a systematic study of seismic precursors, b-value and swarm activity. Temporal variation of b-value is studied using the maximum likelihood method beside CUSUM algorithm. The b-values vary from 0.95 to 1.4 for the deeper (depth ⩾60km) earthquakes, and from 0.85 to 1.3 for the shallower (depth <60km) earthquakes. A sudden drop in the b-value, from 1.4 to 0.9, prior to the occurrence of larger earthquake(s) at the deeper depth is observed. It is also noted that the CUSUM gradient reversed before the occurrence of larger earthquakes. We further examined the seismicity pattern for the period 1988–1995 within a radius of 150km around the epicentre (latitude: 24.96°N; longitude: 95.30°E) of a deeper event M 6.3 of May 6, 1995 in this subduction zone. A precursory swarm during January 1989 to July 1992 and quiescence during August 1992 to April 1995 are identified before this large earthquake. These observations are encouraging to monitor seismic precursors for the deeper events in this subduction zone.

Spatial and temporal evolution of b-values before large earthquakes in Taiwan

We investigate the spatial and temporal variations of b-values before twenty-three earthquakes with ML≥6.0 in the Taiwan region from 1999 to 2009. We estimate the spatial distribution of b-values within a one-year period before the occurrence of investigated earthquakes. It shows that the epicenters of those earthquakes are located predominately in the regions with low b-values relative to the entire study area. In terms of temporal evolutions, the b-values are slightly lower during the year prior to the investigated earthquakes in comparison to the periods two to five years earlier. We propose that these anomalies may offer spatiotemporal constraints for the earthquake forecasting in Taiwan in the future.

Spatial and Temporal Variations of b-Value and Fractal Analysis for the Makran Region

During the last three decades, the eastern segment of the Makran subduction zone has been more active than the western segment. We analyze Makran seismicity using the NEIC catalog from 1973 to 2008. A temporal decrease of b-value in eastern Makran indicates that stress is increasing, which may signal a future sizable earthquake. Also, the spatial variation of b suggests that the western segment is less stressed compared to the eastern segment. It has been observed that the fractal dimension is approximately twice the b value. The seismicity pattern analyzed does hold a key to understanding the seismotectonics of the region.

Spatial and temporal variations of b-values along the East African rift system and the southern Red Sea : F. Kebede & O. Kulhanek, Physics of the Earth & Planetary Interiors, 83(3–4), 1994, pp 249–264

Spatial and temporal variations of b-values along the East African rift system and the southern Red Sea : F. Kebede & O. Kulhanek, Physics of the Earth & Planetary Interiors, 83(3–4), 1994, pp 249–264

B‐Value, aseismic deformation and brittle failure within an isolated geological object: Evidences from a dome structure loaded by fluid extraction

Studies of b‐values are usually performed either at rock sample scale (laboratory experiments) or at crustal scale (earthquakes). But interpretations at crustal scale are extrapolated from small scale experimental laws with well defined boundary conditions, to a larger object with no clear boundary conditions. We examine variations of the b‐value in time and space at spatial (10×10×10 km3) and temporal (20 years) scales intermediate between laboratory analyses and tectonic processes, in a dome structure that is an isolated geological object with defined boundaries and known geomechanical properties. Seismic activity (about 1000 events with magnitude ≤ 4.5) and aseismic displacements (6–7 cm of cumulative subsidence) have been induced by gas extraction in an area where no displacement had previously been reported. We find no agreement between temporal variations in b‐values and results from laboratory experiments: there is no correlation between b‐values and stress histories, nor between b‐values and the spatial migration of seismicity. Aseismic slips introduce anomalies in b‐value behaviour when seismic instabilities are a second order process compared to the whole deformation. These observations imply that when changes in b values have been used for earthquake forecasting, false alarms can be explained by the occurrence of aseismic displacement.

Analysis of the magnitude-frequency distribution for the 1983–1984 earthquake activity of Campi Flegrei, Italy

The magnitude-frequency distribution of earthquakes is one of the statistical relationships most frequently used to study the seismicity of a region. In this paper the Gutenberg-Richter frequency magnitude relationship is applied to the 1983–1984 earthquake sequence of Campi Flegrei, Italy, in order to estimate the space-time variation of the b-value, and its possible correlation with other geophysical parameters in the sequence. The investigated region has been divided into three areas on the basis of differences in seismic activity: (a) to the west of Pozzuoli, where seismicity occurred mostly as swarms; (b) to the east of Pozzuoli, where events mostly included single, high-energy earthquakes; and (c) in the western sector of the Gulf of Pozzuoli. Moreover, b-value estimates have been carried out according to different hypocentral depths of all seismic events in the sequence. The obtained results have shown strong depth variations of the b-value which might reflect important differences in failure conditions at different depths. Furthermore, a certain complexity in the shape of the obtained distribution functions n( M) has been pointed out. Temporal variations of b-value, computed both for the whole region and the different selected areas, seem to be meaningful because they do not depend on the number of shocks ΔN, the data overlap and the magnitude step ΔM. The rates of change of b-value Δb/ Δt, compared with the changing rates of seismic energy release ΔE/ Δt do not show a consistent correlation, hence the Δb/ Δt curve cannot be interpreted as a precursor to the other in any systematic way.