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Understanding the scaling laws of source parameters is a fundamental subject in seismology. This study conducts spectral ratio analysis to estimate the source parameters for 409 shallow crustal earthquakes with Mw 3.2–6.0 in Japan. Subsequently, the source parameter scaling relations are investigated for a wide magnitude range by combining the results of this and previous studies. The spectral ratio method applied in this study provides the finite source properties of the localized area with large slip. The single asperity model, a simple heterogeneous source model with a single localized area with large slip, is used to estimate the stress drop since it can be more suitable to characterize earthquake sources than the standard homogeneous circular source. This investigation calibrates the constant to link the corner frequency and the source radius by comparing the corner frequency and source area estimated by the spectral ratio analyses. This calibrated constant is used to re‐calculate the stress drop of small earthquakes from the corner frequency estimated in previous studies. The stress drop and apparent stress increase with increasing magnitude up to Mw ∼ 5 and become magnitude‐independent for larger earthquakes. The radiation efficiency ranges typically from 0.1 to 1.0 and is independent of magnitude. The slip dependences of the stress drop, apparent stress, radiation efficiency, and fracture energy observed in this study are explained by the ones predicted from the slip‐weakening model incorporating the thermal pressurization effect. Thermal pressurization is one of the possible mechanisms explaining the observed source parameter scaling relations. Plain Language Summary: This study investigates the relationship between earthquake sizes and parameters characterizing the earthquake sources (source parameter scaling relations) to understand the difference between small and large earthquakes. The source parameters are estimated for shallow crustal earthquakes in Japan. Then, the source parameter scaling relations are obtained over a broad magnitude range by combining the results of this and previous studies. This investigation is based on a simple heterogeneous source model rather than the homogeneous circular source model, which has been widely used. A familiar hypothesis is that the sources of small and large earthquakes are physically similar (earthquake similarity). The results suggest that the earthquake similarity holds for earthquakes with a magnitude larger than about 5.0 but does not for small earthquakes. This study demonstrates that the observed source parameter scaling relations can be explained by the source parameter scaling relations predicted from the stress relaxation model incorporating the effect of the pore pressure rise within the fault core by frictional heating during seismic faulting (thermal pressurization of pore fluids). Thermal pressurization of pore fluids can be one of the significant mechanisms explaining the differences in the source parameter scaling relations for small and large earthquakes. Key Points: The single asperity model, a simple heterogeneous source model, is used rather than the standard homogeneous circular source modelThe apparent stress and stress drop increase with magnitude up to Mw ∼ 5 and become magnitude‐independent for larger earthquakesThermal pressurization is one of the possible mechanisms explaining the observed source parameter scaling relations [ABSTRACT FROM AUTHOR]

Earthquakes are one of nature's most devastating disasters. Earthquake prediction is critical in seismology since its success can save lives, property, and infrastructure. Numerous technologies have been proposed to address this issue, including mathematical analysis, artificial intelligence, and machine learning algorithms. Unfortunately, due to earthquakes' dynamic and spontaneous nature, they frequently fail to provide positive results. The study uses deep learning techniques to predict the magnitude of an impending earthquake using eight mathematically calculated seismic indicators derived from Japan, Indonesia, and the Hindu-Kush Karakoram Himalayan (HKKH) region's earthquake catalogs. Three deep learning techniques, including Long Short-Term Memory (LSTM), Bi-directional Long Short-Term Memory (Bi-LSTM), and self-attention-based transformer, have been implemented to model the associations between calculated seismic indicators and potential earthquake incidents. These models have been evaluated with well-known matrices such as the Mean Absolute Error (MAE), Mean Squared Error (MSE), log-cosh loss, and Mean Squared Logarithmic Error (MSLE). The value of these cost functions converges to a small number for all models, indicating that these models effectively predict earthquake magnitudes. When these models were fed with an unknown test dataset from Japan, the LSTM model performed best with the least deviation metrics (MAE = 0.060, MSE = 0.006, log cosh = 0.042 and MSLE = 0.003). Similarly, the Bi-LSTM model delivered the ideal result for the Indonesia earthquake catalog (MAE = 0.073, MSE = 0.009, log cosh = 0.016, and MSLE = 0.009), while the transformer model produced the optimal result for the HKKH region (MAE = 0.062, MSE = 0.006, log cosh = 0.043, and MSLE = 0.003). Predicting earthquake magnitude at various locations using these methodologies produces significant and positive results for magnitudes ranging from 3.5 M to 6.0 M, paving the way for the ultimate robust prediction mechanism, that has not yet been developed. [ABSTRACT FROM AUTHOR]

A monitoring method to grasp the spatio-temporal change in the interplate coupling in a subduction zone based on the spatial gradients of surface displacement rate fields is proposed. I estimated the spatio-temporal change in the interplate coupling along the plate boundary in northeastern (NE) Japan by applying the proposed method to the surface displacement rates based on global positioning system observations. The gradient of the surface velocities is calculated in each swath configured along the direction normal to the Japan Trench for time windows such as 0.5, 1, 2, 3 and 5 yr being shifted by one week during the period of 1997-2016. The gradient of the horizontal velocities is negative and has a large magnitude when the interplate coupling at the shallow part (less than approximately 50 km in depth) beneath the profile is strong, and the sign of the gradient of the vertical velocity is sensitive to the existence of the coupling at the deep part (greater than approximately 50 kmin depth). The trench-parallel variation of the spatial gradients of a displacement rate field clearly corresponds to the trenchparallel variation of the amplitude of the interplate coupling on the plate interface, as well as the rupture areas of previous interplate earthquakes. Temporal changes in the trench-parallel variation of the spatial gradient of the displacement rate correspond to the strengthening or weakening of the interplate coupling. We can monitor the temporal change in the interplate coupling state by calculating the spatial gradients of the surface displacement rate field to some extent without performing inversion analyses with applying certain constraint conditions that sometimes cause over- and/or underestimation at areas of limited spatial resolution far from the observation network. The results of the calculation confirm known interplate events in the NE Japan subduction zone, such as the post-seismic slip of the 2003 M8.0 Tokachi-oki and 2005 M7.2 Miyagi-oki earthquakes and the recovery of the interplate coupling around the rupture area of the 1994 M7.6 Sanriku-Haruka-oki earthquake. The results also indicate the semi-periodic occurrence of slow slip events and the expansion of the area of slow slip events before the 2011 Tohoku-oki earthquake (M9.0) approaching the hypocentre of the Tohoku-oki earthquake. [ABSTRACT FROM AUTHOR]

The great Japanese earthquake (GJE) of March 11, 2011, was a megaevent. The conditions under which such seismic catastrophes occurred are discussed. The regime of the aftershocks of this megaevent is compared with the data on the aftershock sequences which accompanied the Simushir earthquakes (2006 and 2007) and the Andaman earthquake (2004) and with the seismicity behavior in the generalized vicinity of a strong earthquake. The aftershock sequences of the abovementioned strong earthquakes are shown to represent the sets of trend changes in the postshock activity and specific outbursts of seismic activity. Activity outbursts are characterized not only by an increase in the number and energy of events, but also by a decrease in the recurrence plot slope ( b value) and the average earthquake depth. Some such outbursts correspond to the occurrence of strong repeated shocks. A possible mechanism for outbursts of seismic activity is proposed. The possibility of a stronger repeated shock in the vicinity of the megaearthquake of March 11, 2011, is discussed. [ABSTRACT FROM AUTHOR]

Abstract: The long-term data during seven years from January 2001 to December 2007, as observed by the Pacific VLF/LF network consisting of several Japanese stations and one station in Kamchatka, are extensively utilized to perform a statistical correlation study between the lower ionospheric perturbations as detected by subionospheric propagation and earthquakes (EQs). In this paper, we adopt a physical parameter, the maximum seismicity intensity observed (I) to define the strength of an EQ unlike the previously and conventionally used EQ magnitude and depth, which is a combined effect of EQ magnitude and depth, together with the Earth’s surface information and geological condition around the EQ epicenter. After considering EQs only take place on the land because of the use of seismicity and by using the superimposed epoch analysis, it is found for the larger EQs with I from 5 to 7 (we feel serious trembling and we expect serious damage) that the most important VLF/LF parameter, trend (nighttime average amplitude), shows a definite decrease about 10 days before the EQ by exceeding 2σ (σ: standard deviation) criterion; the dispersion shows a maximum about 10 days before the EQ but not exceeding 2σ line and finally the nighttime fluctuation shows an enhancement about 10 days before the EQ (with exceeding the 2σ level). A definite statistical correlation is confirmed between the ionospheric perturbations and I when I is strong enough in a range from 5 to 7. Whereas, there is no significant correlation between the two when I is in a range from 3 to 4. Finally, together with the corresponding results for EQs in the sea, but close to the land, these results are discussed in the light of lithosphere–ionosphere coupling mechanism. [Copyright &y& Elsevier]

Abstract: In the Kanto region, there have been reports of decreasing b-values prior to earthquakes (M ≥5.5). The change of b-values is defined as the difference between the long- and short-term average earthquake magnitudes. A hazard function for moderately large earthquakes has also been proposed. This model was based on earthquakes that occurred between 1982 and 1999, and its effectiveness is measured retrospectively. In order to evaluate the effectiveness of the model through the use of independent data, the verification test is based on earthquakes observed after January 2000. Through the end of 2004, the only event where there was a decrease in mean event size was observed on June 3, 2000. This decrease resulted in a log-likelihood for the proposed model 1.3 units larger than that of the Poisson model, supporting the validity of the proposed model. Without accumulating further examples, we attempted to improve the verification test by expanding the study volume and by lowering the target cutoff magnitude in order to overcome the small sample size. When two other targets from the expanded volume were added, the difference in the log-likelihood (ΔlnL) increased to 3.6. In this case, the information rate per event was about 1.2, larger than that of the model period. Lowering the cutoff magnitude increased ΔlnL to 2.5. These extended tests led to higher confidence in the model with the larger ΔlnL value than did the primary test. From the viewpoint of the per-event information rate, each case involving targets with a magnitude 5.5 and larger resulted in better performance than in the model period. [Copyright &y& Elsevier]