Seismic Energy Rate Research Articles

A Single‐Station Method for Seismic Detection of Slow Earthquakes: Applications to Japan and the Mexican Subduction Zone

AbstractSlow‐earthquake signals are generally smaller than or comparable to noise levels at almost all seismological frequencies. Comprehensive detection of these events requires continuous waveforms from many stations, but such data are not always available, even in regions with high slow‐earthquake activity. We therefore need a simple and stable detection method that is also applicable to regions with sparse seismic observation networks to truly advance our understanding of slow earthquakes. Here, we utilize the proportionality between the seismic energy rate and seismic moment rate of slow earthquakes to develop a slow‐earthquake detection method using broadband waveforms from a single station. We introduce the method and estimate its performance using continuous waveform data in Japan. The new method only detects events when the tectonic tremors occur near the station, for example, 89.1% of the detections have corresponding tectonic tremor activities within 60 km, which suggests that the false‐positive rate is low. We then apply it to waveform data from the Guerrero, Oaxaca, and Jalisco regions along the Mexican subduction zone. The results for the Guerrero and Oaxaca regions are largely consistent with the geodetic and seismological results from a previous study. We also detect many events in the Jalisco region using a permanent station and provide the first seismological report of long‐term slow‐earthquake activity in this region. Some of the large‐scale slow‐earthquake activity that is detected in this study is consistent with the timings of known slow‐slip events, which implies that other unknown slow‐slip events may have occurred when we detected many events.

Shallow Slow Earthquake Episodes Near the Trench Axis off Costa Rica

AbstractSlow earthquakes are mainly distributed in regions surrounding seismogenic zones along the plate boundaries of subduction zones. In the Central American subduction zone, large regular interplate earthquakes with magnitudes of 7–8 occur repeatedly around the Nicoya Peninsula, in Costa Rica, and a tsunami earthquake occurred off Nicaragua, just north of Costa Rica, in 1992. To clarify the spatial distribution of various slip behaviors at the plate boundary, we detected and located very low frequency earthquakes (VLFEs) around the Nicoya Peninsula using a grid‐search matched‐filter technique with synthetic templates based on a regional three‐dimensional model. VLFEs were active in September 2004 and August 2005, mainly near the trench axis, updip of the seismogenic zone. The distribution of VLFEs overlapped with large slip areas of slow slip events. Low frequency tremor signals were also found in high‐frequency seismogram envelopes within the same time windows as detected VLFEs; thus, we also investigated the energy rates of tremors accompanied by VLFEs. The range of scaled energy, which is the ratio of the seismic energy rate of a tremor to the seismic moment rate of accompanying VLFE and related to the rupture process of seismic phenomena, was 10−9–10−8. The along‐dip separation of shallow slow and large earthquakes and the range of the scaled energy off Costa Rica are similar to those in shallow slow earthquakes in Nankai, which shares a similar thermal structure along the shallow plate boundary.

Сильные землетрясения земного шара во II полугодии 2020 г. по данным ФИЦ ЕГС РАН

The data on the seismicity of the Earth in the second half of 2020 at the level of strong earthquakes with magnitudes mb≥6.0 are given according to the data of the Alert Service of the Geophysical Survey RAS. The review also includes information on 54 tangible earthquakes in Russia and five earthquakes in adjacent territories that were felt in the settlements of the Russian Federation. Two of 67 strong earthquakes of the Earth with mb≥6.0 for the period under consideration were registered in the territory of Russia. For 15 strong earthquakes, the Alert Service published Information Messages within one or two days after their occurrence, for 14 earthquakes the information on focal mechanisms is provided. The strongest earthquake of the Earth with MS=7.9 occurred on July, 22 in the region of the Alaska Peninsula. The maximum human casualties and material damage during the study period were the result of the catastrophic intraplate earthquake with MS=6.8, which occurred on October, 30 in the Aegean Sea, near the Samos Island. As a result of the earthquake, 117 people died, 1054 were injured. The strongest earthquake on the territory of Russia was the deep-focus one with mb=6.4, which took place on November, 30 in the Tatar Strait, separating Sakhalin Island from continental Eurasia. The crustal Bystrinsk earthquake on September, 21 with MS=5.2, which occurred in the area of Lake Baikal, was felt with a maximum intensity I=6–7 on the territory of Russia. Comparative analysis of the rate of seismic energy released in the Globe in 2010-2020 showed that its value in the second half of 2020, as well as for 2019-2020 on average, is one of the lowest for the eleven-year period and indicates a seismic calm, which should be replaced by a period of intensification of global seismic and deformation processes

Seismic energy radiation and along-strike heterogeneities of shallow tectonic tremors at the Nankai Trough and Japan Trench

Shallow slow earthquakes have been documented along shallow plate interfaces near trenches. Recent geophysical observation networks located offshore of Japan enable us to analyze shallow tremors in the Nankai Trough and the Japan Trench. Onshore seismic stations are also important for detecting shallow very low frequency earthquakes (VLFEs) and for evaluating their seismicity prior to the deployment of offshore observation networks. This study analyzes data from ocean bottom seismometers to estimate the seismic energy radiation of such tremors, from which we observe along-strike heterogeneity. Tremors with higher seismic energy rates tend to have longer recurrence intervals, which has also been observed for deep tremors. This study also estimates seismic moment releases of shallow VLFEs at the Japan Trench observed by onshore seismic stations using Green's function in a local three-dimensional seismic velocity model. The scaled energy, which is the ratio of the seismic energy (rate) to the seismic moment (rate), is ~10−9. Shallow slow earthquakes located off the Kii Peninsula and Cape Muroto in the Nankai Trough have higher values (10−9–10−8), while shallow slow earthquakes located off the Kii channel in the Nankai Trough and in the Japan Trench have lower values (10−10–10−9), which are similar to the values estimated for deep slow earthquakes. By comparing the cumulative seismic energy of the shallow tremors with the cumulative seismic moment of shallow VLFEs, we evaluate the monitoring of shallow tremors and shallow VLFEs in the Japan Trench, suggesting that monitoring shallow VLFEs based on data from onshore seismic stations could miss many (~90% at most) of the seismic moment releases by small magnitude but frequent events.

Predictability of the Seismic Energy Flux: Southern Europe and the Mediterranean

The paper assessed the predictability of the seismic energy rate and large earthquakes in southern Europe and the Mediterranean according to the data from the United States Geological Survey catalog for 1900–2016. A nonlinear second-order differential equation is used as a mathematical model, and optimization and predictability estimation algorithms are this author’s. The estimates show a high predictability of energy rate trends. For 84 out of 217 large earthquakes in the region, we have found foreshock predictability, and aftershock predictability for 200 earthquakes. The predictability of large earthquakes begins to be seen at small (1.5–7.5 km) radii of hypocenter samples, increases rapidly at medium (15 and 30 km) radii, then more smoothly increases at a radius of 60 km and decreases slightly at a radius of 150 km. The predicted distance in time averages tens of days for foreshock predictability and thousands of days for aftershocks. The results demonstrate good prospects for the approximation–extrapolation approach to the prediction of both earthquakes themselves and the subsequent aftershock decay of seismic activity.

Predictability of the rate of seismic energy in North America

The predictability of the rate of seismicity and strong earthquakes of North America is assessed based on the catalog of the U.S. Geological Survey for 1900–2016. A second-order nonlinear differential equation is used as the mathematical model of the study; the algorithms for optimization and predictability assessment are developed by the author. The conducted estimates show high predictability of the rate of seismic energy. Among 1422 analyzed strong earthquakes, the foreshock predictability is revealed for 120 earthquakes (215 thousand determinations) and the aftershock predictability for 1410 earthquakes (more than 3 million determinations). The predictability related to the strong earthquakes appears at small (1.5–3 km) radius of the samples of hypocenters and increases in terms of the number of the predicted earthquakes with the increase in the radius of the samples. The forecast distances in time are, on average, tens of days for foreshock predictability and thousands of days for aftershock predictability. The obtained results demonstrate a very promising potential of the approximation-extrapolation approach for forecasting both the strong earthquakes themselves and the subsequent aftershock decay of seismic activity.

Predictability of the Rate of Seismic Energy in North America

Predictability of the Rate of Seismic Energy in North America

Прогнозируемость потока сейсмической энергии северо-западного обрамления Тихого океана по данным каталога USGS

Прогнозируемость потока сейсмической энергии северо-западного обрамления Тихого океана по данным каталога USGS

Differences of precursory seismic energy release for the 2007 effusive dome-forming and 2014 Plinian eruptions at Kelud volcano, Indonesia

Early warnings of the timing, style, and size of volcanic eruptions, made on the basis of seismic monitoring, are important for mitigation of the hazards associated with volcanic eruptions. We calculated the rates of seismic energy release at Kelud volcano, Indonesia, preceding both the 2007 effusive lava-dome eruption and the 2014 Plinian eruption. For the 2007 eruption, there was first a step-wise increase in the rate of release of seismic energy, followed by a gradual decrease until the eruption. For the 2014 eruption, the rate of energy release was almost constant until 10days before the eruption, then gradually increased until there was a dramatic acceleration during the last day before the eruption. The total seismic energy released by the 2007 and 2014 eruptions were 3×108J and 2.2×109J, respectively. The relative difference between the ejected volumes of the 2007 and 2014 eruptions is roughly equivalent to that of the total seismic energy released preceding the eruptions. We conducted several trials of the material failure forecast method (FFM), applying it to the square root of the rate of seismic energy released, to assess its usefulness for predicting the timing of eruptions. The predicted onset of the 2007 eruption was one day earlier than the actual eruption and the seismic energy release preceding the actual eruption did not increase dramatically as suggested by the FFM model. Several trials of FFM for the 2014 eruption predicted the onset of the eruption to be three days to two weeks later than the actual eruption. Even as the end time of the FFM time window approaches several hours to 10min before the actual eruption onset, the predicted eruption onset is still 3h later than the actual onset. Thus, the results of our FFM modeling did not show the method to be useful for predicting eruption times for Kelud volcano. The differences of the FFM modeling results for the 2007 and 2014 eruptions likely reflect the differences in the rate of energy release immediately before the two eruptions: a deceleration before the 2007 eruption and an acceleration before the 2014 eruption. These differences may reflect differences in precursory processes for effusive lava-dome and Plinian eruptions.

Performance Evaluation of the Earthquake Detection and Classification Algorithm 2(tS–tP) of the Seismic Alert System of Mexico (SASMEX)

Abstract A performance evaluation of the detection and classification algorithm for earthquake early warning 2( t S – t P ) was conducted to test its reliability and robustness. The Seismic Alert System of Mexico (SASMEX) has used this algorithm since 1991. The algorithm estimates the rate of seismic energy released during two times the ( t S – t P ) period. Based on the energy released, it estimates an empirical magnitude range related to m b . Depending on the estimated m b , either preventive or public alerts are issued. In this article, post facto tests are presented for 61 earthquakes for which SASMEX issued an alert. The algorithm was also tested on 31 earthquakes ( M w >6.0) that occurred in the Mexican subduction zone from 1985 to 2014. These earthquakes occurred outside the coverage of the SASMEX instruments at the time. This dataset includes the 19 September 1985 M w 8.1 Michoacan earthquake and the 9 October 1995 M w 8.0 Colima event. The algorithm was tested also on two great earthquakes: the 22 February 2010 M w 8.8 Maule, Chile, earthquake and the 11 March 2011 M w 9.0 Tohoku, Japan, event. The results of the evaluation of 144 acceleration records of the 61 earthquakes detected from the SASMEX network indicate that 92% of the accelerograms of earthquakes with m b >6.0 have errors in the prediction of magnitude of less than ±0.5, and 83% for m b >5.5. Also, the tests conducted on the 59 acceleration records of 31 earthquakes with M w ≥6.0 indicate that in all cases, with the exception of one strong‐motion record, the events are classified as M w ≥6.0. Thus, the algorithm shows a high level of reliability and robustness. Although the algorithm underestimates the magnitudes of large earthquakes, these events are identified and classified as M w ≥6.0. Thus, an alert would be issued for these great earthquakes. Electronic Supplement: Table of earthquake parameters, performance of Seismic Alert System of Mexico (SASMEX), and specific performance evaluation of the 2( t S – t P ) algorithm.

Spatial distribution of seismic energy rate of tectonic tremors in subduction zones

AbstractThe sizes of deep tectonic tremors have never been accurately evaluated as a physical quantity. Here we estimate tremor size as the band‐limited seismic energy rate at 2–8 Hz, with accurate evaluation of the path attenuation and site amplification of seismic waves in four subduction zones: Nankai, Cascadia, Jalisco, and South Chile. The size‐frequency statistics of seismic energy rate, which are characterized by the median measure for each subregion, are spatially variable. The spatial variations are categorized into three types, with each type corresponding to a different tremor migration behavior. In type A regions where tremor zone is wider, seismic energy rates are highly variable in the dip direction, and tremor activities are usually initiated in the less energetic tremor zone. Some of them further penetrate into the energetic tremor zone and subsequently migrate for long distances in the strike direction. Type B regions are characterized by relatively narrow tremor zones, minor variations in energy rates in the dip direction, and long‐distance migration in the strike direction. Type C regions are characterized by isolated clusters of tremor activities without migration and by independent failure of each small tremor cluster. Given that the spatial distributions of tremor energy rates reflect heterogeneities in the strength of the plate interface, such distributions, which would be controlled by the width of tremor zone, may determine the regional style of slow‐earthquake behavior. Some energetic tremor regions act as switches that trigger large slow slip events, especially in type A regions.

Universality of slow earthquakes in the very low frequency band

AbstractDeep tectonic tremors have been observed together with signals in the very low frequency (VLF) band from 0.02 to 0.05 Hz, which have been identified as VLF events in limited regions of subduction zones. By stacking broadband seismograms relative to the timing of tremors, we have detected similar signals in all regions where tremors occur in western Japan. These signals are inverted to obtain the moment tensor, and the fault‐normal and slip vectors are generally consistent with the geometry of the plate interface and the direction of plate motion. Therefore, these signals are probably radiated by shear slip on the plate interface. The ratio between the seismic energy rate estimated from the tremors and seismic moment rate in the VLF band is almost proportional, with a proportionality constant (i.e., scaled energy) of around 5 × 10−10. The spatial distribution of scaled energy may reflect spatial variations in the frequency‐dependent characteristics of slow deformation.

Blasting-induced seismicity in the European part of Russia

The paper focuses on the increasing contribution of blasting operations to the energy balance of seismic processes. Although the progress in blasting technologies will not produce energy outputs that exceed the energy of natural earthquakes on a global scale, it is shown that in some cases, the regional contribution to seismic energy release by blasting operations is by a few orders of magnitude higher than the energy released by natural earthquakes. In particular, this is valid for the European part of Russia, which is characterized by reasonably weak natural seismic activity. In order to identify the sources of natural seismicity over the European territory of Russia, we present the classification of the industrial blasting operations. The spatial distribution of explosive activities is presented; the consumption of explosives is estimated; and the technology of short-delay mass explosions, which might be helpful for interpretation of seismic records, is described. Zoning the territory of the European part of Russia in terms of the release rate of seismic energy and the peak local magnitudes observed during blasting operations is carried out. It is shown that the hazard level associated with blasting activities does not exceed the corresponding parameters of seismic zoning.

Seismic activity that accompanied the effusive and explosive eruptions during the 2004–2005 period at Volcán de Colima, Mexico

Volcán de Colima is considered the most active in Mexico. A period of large eruptive activity occurred in 2004–2005. It began as a swarm of long-period events (LPs) in late September 2004, indicating the onset of growth of a new lava dome in its crater. Subsequently, avalanches of incandescent material and pyroclastic flows during a period of approximately 2 months occurred. Then, the activity became more explosive with moderate explosions. Finally, swarms of LPs accompanied the magma ascent and extrusion of small domes and vulcanian explosions with pyroclastic flows in 2005. This eruptive period was investigated with a continuous seismic signal study, cross-correlation of LPs and autoregressive analysis of monochromatic LPs. For the vast majority of the explosions, an increase in the rate of seismic energy was observed with the Seismic Spectral Energy Measurement (SSEM) from 1 to 3 Hz, before each explosive event. This increase in energy is proportional to the increase in the rate of LPs, probably as a result of an increase in the emission rate. Applying the material failure forecasting method (FFM) and using SSEM inverse of parameter, the time of the explosions is estimated as the time when the adjusted line reaches the null value. We observe a systematic delay of a few hours between the real time of occurrence of the explosions and the estimated time. This suggests that more complex processes than pure damaging of the plug occur before the explosions. The swarms associated with the large explosions include a large proportion of LPs with similar waveforms. They form a dozen of families which stay during the whole period of activity and which indicate repetitive sources. Some of the families are active only before the explosions and could therefore be used as early warning. Monochromatic LP events occurred during this period, some of them just some hours before an explosion. However, no clear relationship between their occurrence and the explosions could be found.

Fluctuations, trends and scaling of the energy radiated by heterogeneous seismic sources

SUMMARY Computer simulations, based on a heterogeneous seismic source model governed by the overdamped dynamics, reproduce essential aspects of seismicity, both on ‘microscopic’ (local functions, such as slip velocity), and ‘macroscopic’ (global functions, such as seismic energy) level. The present work focuses on relations between these two description levels, using formulation of the seismic energy rate implied by the same model. It is shown that the apparent stress, defined as the seismic energy and the seismic moment ratio, represents the correlation integral of the slip velocity distribution. An auxiliary, simplified, kinematic model of an averaged, pulse-like rupture process is used to derive the scaling relationship for the apparent stress as a function of other ‘macroscopic’ quantities: The seismic moment, MO, the rupture area, A, and the average slip acceleration, g, treated as independent variables. These results explain observed fluctuations and statistical trends of the apparent stress, characterizing both real and simulated earthquake populations.

A macroscopic approach towards earthquake physics: the meaning of the apparent stress

Some theoretical results concerning earthquake parameters are based on simplified seismic source models with uniform distributions of slips along a fault. Here two such results, the meaning of the apparent stress and the seismic energy vs. seismic moment relation, are revised by taking into account fault heterogeneity and interactions related to slip gradients. A theoretical microscopic model of a seismic source, formulated in terms of slip and stress fields, is studied by computer simulations. Formulation of the seismic energy rate implied by the microscopic model, together with an auxiliary kinematic model of a pulse-like rupture process, is used to derive a scaling relationship for the seismic energy as a function of other ‘macroscopic’ quantities: the seismic moment, rupture area, and the average slip acceleration, treated as independent variables. This result explains observed fluctuations and statistical trends of the seismic energy in both real and simulated earthquake populations.

Energy exchange between seismic and ultrasonic vibrations in an elastic medium with a microstructuret

The flow rate of seismic energy under conditions of long-wave-short-wave resonance in granular geomaterials (soil or fissured mountain rock) is calculated using a continuous elastic non-linear model with microrotations.

累層採炭に伴う地震活動

The seismicity which was brought about by mining of multiple coal seam was measured at Sunagawa Coal Mine in Hokkaido over nine months in 1978. The magnitude distribution of seismic events was consistent with the Gutenberg-Richter's formula whose b-value was estimated as 1.3. The spatial rate of seismic energy associated with mining of the upper seam which was underwent at first was several times higher than the successive mining of the lower seams. On the other hand the spatial rate of energy released by mining of multiple seam was determined from the face element method. A numerical experiment showed that the ratio of the energy release rate at the upper seam to that of the lower seam had close agreement with the ratio of the seismic energy release rates that were measured. These results imply that the spatial rate of seismic energy induced by mining may be proportional to that of energy released from rock around underground excavations. On the basis of this observation mining sequence and mining method are discussed which can aid to prevent severe seismic event including rock burst.

Rotational Inertia of Continents: A Proposed Link between Polar Wandering and Plate Tectonics

A mechanism is proposed whereby displacement between continents and the earth's pole of rotation (polar wandering) gives rise to latitudinal transport of continental plates (continental drift) because of their relatively greater rotational inertia. When extended to short-term polar wobble, the hypothesis predicts an energy change nearly equivalent to the seismic energy rate.