Earthquake Energy Release Research Articles

Predicting earthquakes: The Mw9.0 Tohoku Earthquake and historical earthquakes in Northeastern Japan

A magnitude 7.3 foreshock occurred two days before the magnitude 9.0 Tohoku Earthquake. The energy release of earthquakes within two days after the M7.3 earth- quake is obviously different from the aftershocks of the Mw9.0 earthquake. But guided by historical earthquake experience, seismologists regarded the M7.3 earthquake as the main shock rather than a foreshock of another greater earthquake. Based on the analysis of historical earthquakes in coastal areas of northeastern Japan, the recurrence time of earth- quakes is in quasi-periods of decadal or centennial scale. These quasi-periods are related to fault rupture along subduc- tion zones located in marine environments adjacent to the coast. The probabilistic prediction for future earthquakes made by Japanese seismologists using historical earthquake data is based on a decadal scale quasi-period. It is difficult, however, to make relatively reliable predictions about the recurrence interval of rare great earthquakes based on historical earth- quakes due to the very long intervals between large magni- tude quakes and the limited historical and scientific records about their characteristics.

The dependence of earthquake frequency magnitude relationship and strain energy release upon the focal depth in Hindu Kush region

The dependence of earthquake frequency magnitude relationship and the strain energy release upon the focal depth in Hindu Kush region lias been studied based on U.S.C.G.S. data during the years 1903-1971 (March) and the results have been compared with those of the other investigators for European and Japanese region. It is seen that there is no positive evidence for the decrease of b in Gutenberg-Ricliter's frequency magnitude relationship with the focal depth. The temporal variation of the elastic strain rebound also for these data does not show the same characteristic pattern as reported by Benioff for the deep focus earthquakes. Emphasis is given also to some facts relating to the seismotectonic regime of Hindu Kusli area.

Deep-seated faults and lineaments, and the location of earthquake epicenters in the Russian northeast on land

This paper summarizes the available geological and geophysical material for faults as regards their role in the seismic process. The entirety of the geological and geophysical evidence is used to reveal hidden faults, which are important in influencing the spatial distribution of earthquakes, and to produce a map of the major earthquake-generating faults and lineaments in the Russian northeast. As well as the occurrence of earthquakes at known faults that have surface expression, we find that seismicity tends to occur at the hidden faults and lineaments we have identified, as well as at intersections of faults. We made a quantitative assessment of the relationship of seismicity to tectonic fragmentation of the crust, correlating the density and discordance measure for faults to indicators of seismic activity (rate and energy release of earthquakes per unit area) for the southeast flank of the Okhotsk-Lena seismic region. The results obtained in this study revealed some features in the spatial distribution of earthquakes occurring on land in the Okhotsk-Lena seismic region: the maximum level of seismic activity occurs in areas with moderate values of the discordance measure for faults (12 < ‖D‖ ≤ 18) as identified from gravity data and in zones of increased horizontal gradients of the lines of equal discordance. At these locations, the greatest probability of earthquake occurrence for events of energy class K ≥ 12 corresponds to moderate values of the density of faults visible at the surface (0.12 < τ ≤ 0.16 km−1).

Spatial Distribution of Earthquake Energy Release in the Central United States from a Global Point of View

Research Article| January 01, 2008 Spatial Distribution of Earthquake Energy Release in the Central United States from a Global Point of View Qingwen Miao; Qingwen Miao Center for Earthquake Research and Information University of Memphis 3876 Central Avenue, Suite 1 Memphis, Tennessee 38152 qingmiao@memphis.edu (Q.M.) clangstn@memphis.edu (C.L.) Search for other works by this author on: GSW Google Scholar Charles A. Langston Charles A. Langston Center for Earthquake Research and Information University of Memphis 3876 Central Avenue, Suite 1 Memphis, Tennessee 38152 qingmiao@memphis.edu (Q.M.) clangstn@memphis.edu (C.L.) Search for other works by this author on: GSW Google Scholar Author and Article Information Qingwen Miao Center for Earthquake Research and Information University of Memphis 3876 Central Avenue, Suite 1 Memphis, Tennessee 38152 qingmiao@memphis.edu (Q.M.) clangstn@memphis.edu (C.L.) Charles A. Langston Center for Earthquake Research and Information University of Memphis 3876 Central Avenue, Suite 1 Memphis, Tennessee 38152 qingmiao@memphis.edu (Q.M.) clangstn@memphis.edu (C.L.) Publisher: Seismological Society of America First Online: 14 Jul 2017 Online ISSN: 1938-2057 Print ISSN: 0895-0695 © 2008 by the Seismological Society of America Seismological Research Letters (2008) 79 (1): 33–40. https://doi.org/10.1785/gssrl.79.1.33 Article history First Online: 14 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Qingwen Miao, Charles A. Langston; Spatial Distribution of Earthquake Energy Release in the Central United States from a Global Point of View. Seismological Research Letters 2008;; 79 (1): 33–40. doi: https://doi.org/10.1785/gssrl.79.1.33 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search Most of the Earth's seismicity is understood in terms of the major elements of plate tectonics (Cox and Hart 1986). Interaction of plates at spreading ridges, transform faults, and subduction zones controls most of the strain accumulation that gives rise to earthquakes (Turcotte and Schubert 1982). The earthquakes themselves are the products of complex physical processes involving friction and fracture mechanics that ultimately result in the release of elastic energy, some of which is released through seismic wave radiation (Kanamori 1977; Rice 1980; Kanamori et al. 1998; McGarr 1999; Abercrombie et... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Probabilistic Location of Seismic Sequences in Heterogeneous Media

We have developed a method for the Bayesian location of seismic sequences in 3D heterogeneous velocity models. The method is based on a Bayesian algorithm for single earthquake location. Joint location of seismic sequences is performed by summing the probability density functions for individual earthquake locations. One of the main features of the method is the ability to accumulate travel times in the heterogeneous model, as a function of both the seismic stations and the grid points, simulating the seismogenic volume. The ability to compute travel times just once, separately from the location process, allows for fast 3D locations. This is a very attractive feature for real-time monitoring. Probabilistic location of seismic sequences, visualized in terms of contours of earthquake density, moment, and energy release, etc., can be obtained to give a much more seismotectonic insight than classical location algorithms. The continuous character of the output quantities is particularly indicated for seismic-network-testing purposes. It is in fact possible to compute the response of the location procedure, given the seismic network geometry, to various input earthquake distributions. Some applications of the method are also shown in this work, both to the location of synthetic earthquakes and of real sequences. Seismic sequences at Vesuvius and Campi Flegrei volcanic areas (southern Italy) have been located by the probability algorithm, allowing a better picture of the primary seismogenic structures. We also apply the method to assess the resolution of the operating monitoring networks at the two areas.

Local seismic hazard assessment in areas of weak to moderate seismicity—case study from Eastern Germany

Generally the seismic hazard of an area of interest is considered independent of time. However, its seismic risk or vulnerability, respectively, increases with the population and developing state of economy of the area. Therefore, many areas of moderate seismic hazard gain increasing importance with respect to seismic hazard and risk analysis. However, these areas mostly have a weak earthquake database, i.e., they are characterised by relative low seismicity and uncertain information concerning historical earthquakes. In a case study for Eastern Thuringia (Germany), acting as example for similar places in the world, seismic hazard is estimated using the probabilistic approach. Because of the lack of earthquakes occurring in the recent past, mainly historical earthquakes have to be used. But for these the actual earthquake sources or active faults, needed for the analysis, are imprecisely known. Therefore, the earthquake locations are represented by areal sources, a common practice. The definition of these sources is performed carefully, because their geometrical shape and size (apart from the earthquake occurrence model) influence the results significantly. Using analysis tools such as density maps of earthquake epicentres, seismic strain and energy release support this. Oversizing of areal sources leads to underestimation of seismic hazard and should therefore be avoided. Large location errors of historical earthquakes on the other hand are represented by several alternative areal sources with final superimposition of the different results. In a very similar way information known from macroseismic observations interpreted as source rather than as site effects are taken into account in order to achieve a seismic hazard assessment as realistic as possible. In very local cases the meaning of source effects exceeds those of site effects very likely. The influence of attenuation parameter variations on the result of estimated local seismic hazard is relatively low. Generally, the results obtained by the seismic hazard assessment coincide well with macroseismic observations from the thoroughly investigated largest earthquake in the region.

Earthquake activity and hazard in the Carpathian Basin II

Based on a complete dataset of the average magnitude M, the recurrence curve predicts an earthquake of magnitude M = 5 every one year, an earthquake of magnitude M = 6 every ten years, and an earthquake of magnitude M = 7 every one hundred years in the Carpathian Basin on average. The curve of elastic energy release of earthquakes does not indicate any noticeable periodicity in the Carpathian Basin based on the observations of nearly 500 years (1500- 1995). The average yearly energy release is 6.1E+13 joule in the whole Basin and the contribution of the Haromszek-Vrancea region to this amount is 4.8E+13 joule/year, while 1.3E+13 joule/year is the product of the remaining large part of the studied area. That is the vast portion of seismic energy is released in an area of only about 6% of the whole Carpathian Basin. According to the results of probabilistic seismic hazard estimations the highest hazard is expected in the region of Haromszek-Vrancea (Romania), where the expected peak horizontal ground accel...

Surface loading and triggered earthquakes in the Koyna–Warna region, western India

Earthquakes of M≥5.0 continue to occur in the vicinity of Koyna reservoir in western India, the largest known case of Reservoir Triggered Earthquakes (RTS). The region remains seismically active even after four decades of the impounding of the Koyna reservoir. The earthquakes occur repeatedly along two major fault systems in NE–SW and NW–SE directions. We performed cross-correlation analysis between time series of the Koyna reservoir levels and the strain factor (energy 1/2) calculated for earthquakes of M≥3.0 occurring in the region during 1963–1999. Four time windows of 5 years or more are selected for cross-correlation to predict the periodicities, if any, in the seismic energy release caused by the annual reservoir water level fluctuations. A similar analysis was performed for the newly-impounded Warna reservoir, 25 km south of the Koyna dam. Our results suggest that the initial seismicity in the Koyna region during 1963 was triggered after the region attained steady state pore pressure by diffusion processes, particularly occurring along vertical strike-slip faults. Subsequently, major episodes of earthquake energy release until 1999 show a periodic behavior related to the annual filling of both the Koyna and Warna reservoirs. Two stages of earthquake energy release are evident till 1996 and coincide with annual filling and draining cycles of the reservoirs. Since 1996, the seismic energy release episodes correlate mostly with the draining cycle of the reservoir levels indicating a shift in the present day earthquake activity in the region, which may be due to a combined effect of the Koyna and Warna reservoirs. To explain the causal relationship between the reservoir water level fluctuations at the surface and earthquakes at hypocentral depths in terms of diffusion processes, we modeled the pore pressure front diffusion with time, in an inhomogeneous medium. It is seen that a water level change of the order of 1 m in 5 days in the surface loading can propagate 5–15% of pore pressure front, corresponding to 0.75–2.25 bar, to the hypocentral depth of 6–8 km in the presence of a vertical conducting fault. These small stress perturbations are sufficient to trigger seismicity on pre-existing, critically stressed faults in the Koyna–Warna region.

On the spatio temporal distribution of global seismicity and rotation of the earth — A review

This article reviews the development of the study of relationship between the earth's rotation and the spatio-temporal distribution of global seismicity by stationary model of seismicity rates and annual seismic energy released. Observed variations of seismic energy release in shallow, intermediate and deep focus earthquakes and their frequency distribution confirms this correlation. The peaks of these parameters are controlled by the earth rotation. There exists a phase relationship among earth's rotation rate minima and maxima with the maxima (peaks) of the above parameters as well as Thrust (T) and the strike slip (S) dominating periods of global seismicity. In order to compare our results with observations, the space-time dependence of the frequency of earthquakes and annual energy release has been established. The results are in very good agreement with previous studies and further enhance our knowledge for global seismicity distribution.

Determination of earthquake energy release in the Eastern Mediterranean region

Seismic energy radiated by earthquakes in the Eastern Mediterranean region is estimated using the short‐period (50 samples per second) seismic recordings made by the Israel Seismic Network during 1990–1997. Our data set is the whole S‐wave window (from Sn until Lg falls to less than twice the noise level) from 133 earthquakes with a high signal‐to‐noise ratio. We obtained the attenuation function (1.850 ± 0.005) log R + (0.00460 + 0.00005)R log e + 0.05, where the distance range is 50 ≤ R ≤ 1500 km. We tested the dependence of the attenuation function on the azimuth and the distance. Despite the different propagation paths of the waves travelling through the continental crust of the Arabian Shield to the east or the intermediate crust of the Mediterranean Sea to the west, we show that from a statistical point of view the attenuation functions are similar. The energy estimation involves time‐domain integration of the squared ground‐motion velocity, assuming that the attenuation is known, following the method of Kanamori . (1993). For the magnitude range 3.0 ≤ mB ≤ 6.2 (magnitude determined by the National Earthquake Information Service, NEIS), we obtained the magnitude–energy relationship log E0 = (2.09 ± 0.10)mB + (8.86 ± 0.42). Comparison of the seismic energy and the seismic moment suggests that E ∝ M00.19 and that Orowan's stress drop increases as M00.19. A refinement of the results is expected with the application of the method of Mayeda & Walter (1996) for energy estimation from coda envelopes using a large data set of broad‐band observations.

Determination of Seismic Energy from Lg Waves

Seismic energy is a physical concept related to broadband information on the source radiation; this is different from seismic moment, which is related to low-frequency information. Improved estimates of seismic moment and radiated energy can improve the scientific framework for interpreting observed seismicity in terms of physical source processes. This study evaluates the utility of regional Lg waves, the dominant feature of seismograms for regional earthquakes, for the estimation of radiated seismic energy. The rms Lg, which is defined as the root mean square of Lg -wave ground velocity within a certain group velocity range, is proportional to the square root of Lg -wave-radiated energy flux. We find that rms Lg is a good quantity for estimating the energy release of earthquakes because a large fraction of the total seismic energy is radiated as Lg waves. We scale the network-averaged rms Lg value to a reference distance of 100 km for a set of 52 earthquakes in the northeastern United States, using an empirically-derived relation between rms Lg and epicentral distance. We apply the source parameters, estimated for these earthquakes, to Boatwright's deceleration source model and calculate the total seismic energy expected to have been radiated by each event, assuming it can be modeled by this source. We then obtain for earthquakes in the northeastern United States the scaling of the total radiated seismic energy of earthquakes with network-averaged rms Lg values. From synthetic seismograms, it is found that different velocity structures have an effect on the efficiency of Lg -wave radiation. Using measurements of rms Lg made from synthetics, we find that the vertical strike-slip source tends to radiate less Lg -wave energy than other source mechanisms. Manuscript received 4 February 1998.

Numerical calculations of tectonic stress field of Chinese mainland and its neighboring regions and their applications to explanation of seismic activity

This paper made a numerical simulation to the basic tectonic stress field of Chinese mainland and its neighboring region using the visco-elasticity finite element model and the new published displacement rate result. Main contents include the simulation of maximum shear stress and its varying rate, the maximum shear strain and its varying rate, the shear strain energy density and its varying rate. In view of the high inhomogeneous distribution character of seismicity in space and time in Chinese mainland and its neighboring area, the normalized background energy value was given by means of normalized treatment to the earthquake energy release in the eastern and western parts of Chinese mainland. And the comparison of the simulation result with the actual seismicity was made. The results show that the simulation values can explain well the earthquake distribution character of Chinese mainland and its neighboring area.

Distinguishing between random and nonrandom patterns in the energy release of great earthquakes

Romanowicz [1993] suggested that great earthquakes alternate in a predictable fashion between strike‐slip and dip‐slip mechanisms on a 20–30 year cycle. We investigate whether or not the observed pattern of shifting predominance between strike slip and dip slip is capable of frequent reproduction by random simulation. To accomplish this, we randomly drew strike‐slip and dip‐slip events in the same proportion as in the historic record and determined how frequently a pattern of predominance similar to the historic record is generated. Out of 1000 simulations a pattern similar to the historic record was observed 183 times. This throws considerable doubt on Romanowicz's [1993] conslusion that a mechanism is at work producing the distribution she observed of great earthquakes. The difficulty in coming to conclusions from data of the type used by Romanowicz [1993] is explored, along with the psychological literature on the difficulty of detecting random and nonrandom patterns from relatively small amounts of information.

Determination of S-wave energy release of earthquakes in the region of Friuli, Italy

Summary The S-wave energy released by the 1976 Friuli earthquake (ML 6.6) and nine aftershocks with local magnitudes ranging between 4.7 and 6.4 was estimated using strong-motion records near the source and at regional distances. To determine the seismic energy radiated from the source, we corrected the spectral records for attenuation along the path using the Q-frequency relation Q= 20.4f1.01, and for the effect of near-surface attenuation using specific values of k0 reported by Castro et al. (1996) for the recording sites of the region. The remaining path effects were separated from the source functions using a non-parametric inversion. The displacement source functions show an intermediate ω-1 fall-off before a high-frequency fall-off of ω-2, which provides more energy compared with a single ω-2 decay. When we compare the seismic energy (Es) evaluated by integrating the square of the velocity source spectra with the energy estimated from the local magnitudes via Gutenberg & Richter's (1956) relation, we find that Es radiated from the source is, on average, a factor of 6 higher than that obtained from ML. In addition, comparing the seismic moments (Mo) reported in previous studies (Cipar 1981; Cocco & Rovelli 1989) with Es, we observed that Es, increases proportionally to Mo1.24. This rate of increase of the seismic energy with moment indicates that the Orowan stress drop also increases with Mo. The apparent stress calculated with the ratio Es/Mo is also greater than half the Brune stress drop (σa > Δσ/2), suggesting that, for the thrust faulting earthquakes of Friuli, the final stress was greater than the frictional stress during the 1976 sequence.

Distribution of the lunisolar tidal elastic stress tensor components within the Earth's mantle

A set of second order spheroidal Love-Shida numbers ( h( r), k( r), l( r)) and their radial derivatives were determined for the case of a symmetric, non-rotating, elastic, isotropic (SNREI) Earth with a liquid core. By these means, the stress tensor components from the surface to the core-mantle boundary (CMB) were calculated for the case of zonal, tesseral and sectorial tides. The possible dependence of geophysical phenomena on the lunisolar effect is discussed for the three different kinds of tides. The case of tidal triggering of earthquakes is discussed in more detail. Since the tidal potential and its derivatives are coordinate dependent and the zonal, tesseral and sectorial tides have different distributions on and within the Earth, the lunisolar stress cannot influence the break-out of every seismological event in the same degree. A correlation between earthquake energy release and the lunisolar effect can exist in some cases where the seismic area is well determined and has either one seismic source or severe similar ones. Particularly in volcanic areas, where the seismic activity is connected to the volcano's activity, or in the case of some aftershock swarms, significant correlation was found by different authors.

Seismic energy release in Mexican subduction zone earthquakes

We estimated radiated seismic energy ( Es ) from 18 shallow, thrust Mexican subduction zone earthquakes (4 × 1022 ≦ M ≦ 1.1 × 1028 dyne-cm; 11 ≦ H ≦ 37 km) using digital accelerograms from the Guerrero Accelerograph Array and neglecting stations with large site effects. Es is computed by integrating squared velocity spectra, after applying geometrical spreading and Q corrections. We discarded epicentral recordings for the largest Michoacan event. We find that log ( Es / M ) = −4.152 ± 0.275, which gives a median value of Es / M and apparent stress (σ a ) of 7.1 × 10−5 and 24 bars, respectively. The median Es / M value is in accordance with Gutenberg and Richter's (G-R) (1956) formula for Es , in which Es / M = 5 × 10−5 is implicit. Worldwide Es / M data, where Es is computed from local records, mostly fall between 5 × 10−5 and 5 × 10−4 for events with M ≧ 1022 dyne-cm. On the other hand, Es / M values, generally, lie between 5 × 10−6 and 5 × 10−5, if Es is estimated from teleseismic records. Especially anomalous are the Es / M data from Kikuchi and Fukao (1988) for large and great earthquakes, which fall near 5 × 10−6. Thus, while Es from local data suggests that the G-R relation seldom overestimates seismic energy release, the teleseismic data point to the contrary. The cause of this discrepancy may lie in the difficulty of resolving incoherent radiation from the fault and inappropriate choice of t * in the analysis of teleseismic data.

Spatiotemporal Patterns in the Energy Release of Great Earthquakes

For the past 80 years, the energy released in great strike-slip and thrust earthquakes has occurred in alternating cycles of 20 to 30 years. This pattern suggests that a global transfer mechanism from poloidal to toroidal components of tectonic plate motions is operating on time scales of several decades. The increase in seismic activity in California in recent years may be related to an acceleration of global strike-slip moment release, as regions of shear deformation mature after being reached by stresses that have propagated away from regions of great subduction decoupling earthquakes in the 1960s.

Determination of earthquake energy release and ML using TERRAscope

We estimated the energy radiated by earthquakes in southern California using on-scale very broadband recordings from TERRAscope. The method we used involves time integration of the squared ground-motion velocity and empirical determination of the distance attenuation function and the station corrections. The time integral is typically taken over a duration of 2 min after the P-wave arrival. The attenuation curve for the energy integral we obtained is given by q(r) = cr^(−n)exp(−kr)(r^2 = Δ^2 + h_(ref)^2) with c = 0.49710, n = 1.0322, k = 0.0035 km^(−1), and h_(ref) = 8 km, where Δ is the epicentral distance. A similar method was used to determine M_L using TERRAscope data. The station corrections for M_L are determined such that the M_L values determined from TERRAscope agree with those from the traditional optical Wood-Anderson seismographs. For 1.5 6.5, M_L saturates. The ratio E_S/M_0 (M_0: seismic moment), a measure of the average stress drop, for six earthquakes, the 1989 Montebello earthquake (M_L = 4.6), the 1989 Pasadena earthquake (M_L = 4.9), the 1990 Upland earthquake (M_L = 5.2), the 1991 Sierra Madre earthquake (M_L = 5.8), the 1992 Joshua Tree earthquake (M_L = 6.1), and the 1992 Landers earthquake (M_w = 7.3), are about 10 times larger than those of the others that include the aftershocks of the 1987 Whittier Narrows earthquake, the Sierra Madre earthquake, the Joshua Tree earthquake, and the two earthquakes on the San Jacinto fault. The difference in the stress drop between the mainshock and their large aftershocks may be similar to that between earthquakes on a fault with long and short repeat times. The aftershocks, which occurred on the fault plane where the mainshock slippage occurred, had a very short time to heal, hence a low stress drop. The repeat time of the major earthquakes on the frontal fault systems in the Transverse Ranges in southern California is believed to be very long, a few thousand years. Hence, the events in the Transverse Ranges may have higher stress drops than those of the events occurring on faults with shorter repeat times, such as the San Andreas fault and the San Jacinto fault. The observation that very high stress-drop events occur in the Transverse Ranges and the Los Angeles Basin has important implications for the regional seismic potential. The occurrence of these high stress-drop events near the bottom of the seismogenic zone strongly suggests that these fault systems are capable of supporting high stress that will eventually be released in major seismic events. Characterization of earthquakes in terms of the E_S/M_0 ratio using broadband data will help delineate the spatial distribution of seismogenic stresses in the Los Angeles basin and the Transverse Ranges.

Time-lag of the earthquake energy release between three seismic regions

Three complete data sets of strong earthquakes (M≥5.5), which occurred in the seismic regions of Chile, Mexico and Kamchatka during the time period 1899–1985, have been used to test the existence of a time-lag in the seismic energy release between these regions. These data sets were cross-correlated in order to determine whether any pair of the sets are correlated. For this purpose statistical tests, such as theT-test, the Fisher's transformation and probability distribution have been applied to determine the significance of the obtained correlation coefficients. The results show that the time-lag between Chile and Kamchatka is −2, which means that Kamchatka precedes Chile by 2 years, with a correlation coefficient significant at 99.80% level, a weak correlation between Kamchatka-Mexico and noncorrelation for Mexico-Chile.

Periodicity in seismicity: examination of four catalogs

Seismic activity in four different catalogs is examined for periodicity, both in terms of yearly energy release and number of earthquakes per year. The four catalogs examined cover different areas in different time windows: the Mohns Ridge (a segment of the northern Mid-Atlantic Ridge) (1960–1988), earthquakes felt in Norway (1891–1989), earthquakes offshore Western Norway (1980–1989) and finally seismic energy release from global earthquakes with magnitudes greater then or equal to 7.9 for the years 1898–1977. A period of around 10 years is found in all catalogs and there is a clear correlation between seismicity felt in Norway and global seismic energy release. The correlation in the periodicities of the seismic activity found in these catalogs indicates a global cause for changes in seismicity.