scholarly journals Spatial Variations in Seismicity Characteristics in and Around the Source Region of the 2019 Yamagata-Oki Earthquake, Japan

2020 ◽  
Author(s):  
Taku Ueda ◽  
Aitaro Kato ◽  
Yoshihiko Ogata ◽  
Lina Yamaya
Keyword(s):  
Source Region ◽  
B Value ◽  
Spatial Variations ◽  
Japan Meteorological Agency ◽  
Earthquake Catalog ◽  
Shear Strain Rate ◽  
Study Region ◽  
Etas Model ◽  
Seismicity Rate ◽  
Background Seismicity

Abstract The 2019 {\text{M}}_{\text{j}} 6.7 Yamagata-Oki Earthquake occurred adjacent to the northeastern edge of the source region of the 1964 {\text{M}}_{\text{j}} 7.5 Niigata Earthquake, offshore of Yamagata Prefecture, Japan. Few aftershocks occurred in the source region of the Yamagata-Oki earthquake immediately following the Niigata earthquake, and the recent seismicity rate in this region is extremely low compared with that of the surrounding region. This spatial variation in seismicity may allow us to elucidate plausible physical processes that shape the spatiotemporal evolution of these shallow-crustal environments. Here, we investigate the spatial variations in seismicity characteristics by applying the HIerarchical Space–Time Epidemic Type Aftershock Sequence (HIST-ETAS) model to an earthquake catalog compiled by the Japan Meteorological Agency for events in and around the Yamagata-Oki earthquake rupture region. We compare spatial variations in the background seismicity rate and aftershock productivity estimated from the HIST-ETAS model with the geophysical features in the study region. The background seismicity rate is high along the eastern margin of the Sea of Japan and correlates well with a previously identified zone that possesses a high geodetic shear strain rate. The two major earthquakes occurred in and around an active shear zone, suggesting that the background seismicity rate may serve as a key parameter for evaluating seismic hazard across the Japanese Archipelago. Furthermore, the source region of the Yamagata-Oki earthquake has a higher aftershock productivity, lower b-value, and lower seismic-wave velocity than that of the Niigata earthquake. We interpret this low-velocity zone to be a well-developed damaged rock that resulted in both a reduction in the b-value and an increase in aftershock productivity based on previous laboratory experiments and numerical results; this damage makes the rock more ductile at the macroscopic scale. The higher ductility in the source region of the Yamagata-Oki earthquake may have worked as a soft barrier against the propagation of dynamic rupture that occurred during the Niigata earthquake.

scholarly journals Spatial variations in seismicity characteristics in and around the source region of the 2019 Yamagata-Oki Earthquake, Japan

2020 ◽  
Author(s):  
Taku Ueda ◽  
Aitaro Kato ◽  
Yoshihiko Ogata ◽  
Lina Yamaya
Keyword(s):  
Strain Rate ◽  
Source Region ◽  
Spatial Variations ◽  
Japan Meteorological Agency ◽  
The Sea Of Japan ◽  
Earthquake Catalog ◽  
Study Region ◽  
Etas Model ◽  
Seismicity Rate ◽  
Background Seismicity

Abstract The 2019 MJ 6.7 Yamagata-Oki earthquake occurred adjacent to the northeastern edge of the source region of the 1964 MJ 7.5 Niigata earthquake, offshore of Yamagata Prefecture, Japan. Few aftershocks occurred in the source region of the Yamagata-Oki earthquake immediately following the Niigata earthquake, and the recent seismicity rate in this region is low compared with the source region of the Niigata earthquake. This spatial variation in seismicity may allow us to elucidate plausible physical processes that shape the spatiotemporal evolution of these shallow-crustal environments. Here, we investigate the spatial variations in seismicity characteristics by applying the HIerarchical Space–Time Epidemic Type Aftershock Sequence (HIST-ETAS) model to an earthquake catalog compiled by the Japan Meteorological Agency for events in and around the Yamagata-Oki earthquake rupture region. We compare spatial variations in the background seismicity rate and aftershock productivity estimated from the HIST-ETAS model with the geophysical features in the study region. The background seismicity rate is high along the eastern margin of the Sea of Japan and correlates well with a previously identified zone that possesses a high geodetic E-W strain rate. The two major earthquakes occurred in and around a high E-W strain rate zone, suggesting that the background seismicity rate may serve as a key parameter for evaluating seismic hazard across the Japanese Archipelago. Furthermore, the source region of the Yamagata-Oki earthquake has a higher aftershock productivity, lower e-value, and lower seismic-wave velocity than that of the Niigata earthquake. We interpret this low-velocity zone to be a well-developed damaged rock that resulted in both a reduction in the b-value and an increase in aftershock productivity based on previous laboratory experiments and numerical results; this damage makes the rock more ductile at the macroscopic scale. The higher ductility in the source region of the Yamagata-Oki earthquake may have worked as a barrier against the propagation of dynamic rupture that occurred during the Niigata earthquake.

scholarly journals Spatial variations in seismicity characteristics in and around the source region of the 2019 Yamagata-Oki Earthquake, Japan

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Taku Ueda ◽  
Aitaro Kato ◽  
Yosihiko Ogata ◽  
Lina Yamaya
Keyword(s):  
Strain Rate ◽  
Source Region ◽  
Spatial Variations ◽  
Japan Meteorological Agency ◽  
The Sea Of Japan ◽  
Earthquake Catalog ◽  
Study Region ◽  
Etas Model ◽  
Seismicity Rate ◽  
Background Seismicity

AbstractThe 2019 $${M}_{j}$$ M j 6.7 Yamagata-Oki earthquake occurred adjacent to the northeastern edge of the source region of the 1964 $${M}_{j}$$ M j 7.5 Niigata earthquake, offshore of Yamagata Prefecture, Japan. Few aftershocks occurred in the source region of the Yamagata-Oki earthquake immediately following the Niigata earthquake, and the recent seismicity rate in this region is low compared with the source region of the Niigata earthquake. This spatial variation in seismicity may allow us to elucidate plausible physical processes that shape the spatiotemporal evolution of these shallow-crustal environments. Here, we investigate the spatial variations in seismicity characteristics by applying the HIerarchical Space–Time Epidemic Type Aftershock Sequence (HIST-ETAS) model to an earthquake catalog compiled by the Japan Meteorological Agency for events in and around the Yamagata-Oki earthquake rupture region. We compare spatial variations in the background seismicity rate and aftershock productivity estimated from the HIST-ETAS model with the geophysical features in the study region. The background seismicity rate is high along the eastern margin of the Sea of Japan and correlates well with a previously identified zone that possesses a high geodetic E–W strain rate. The two major earthquakes occurred in and around a high E–W strain rate zone, suggesting that the background seismicity rate may serve as a key parameter for evaluating seismic hazard across the Japanese Archipelago. Furthermore, the source region of the Yamagata-Oki earthquake has a higher aftershock productivity and lower seismic-wave velocity than that of the Niigata earthquake. We interpret this low-velocity zone to be a well-developed damaged rock that resulted in an increase in aftershock productivity based on previous laboratory experiments and numerical results; this damage makes the rock more ductile at the macroscopic scale. The higher ductility in the source region of the Yamagata-Oki earthquake may have worked as a barrier against the propagation of dynamic rupture that occurred during the Niigata earthquake.

scholarly journals Spatial variations in seismicity characteristics in and around the source region of the 2019 Yamagata-Oki Earthquake, Japan

2020 ◽  
Author(s):  
Taku Ueda ◽  
Aitaro Kato ◽  
Yoshihiko Ogata ◽  
Lina Yamaya
Keyword(s):  
Strain Rate ◽  
Source Region ◽  
Spatial Variations ◽  
Japan Meteorological Agency ◽  
The Sea Of Japan ◽  
Earthquake Catalog ◽  
Study Region ◽  
Etas Model ◽  
Seismicity Rate ◽  
Background Seismicity

Abstract The 2019 Mj 6.7 Yamagata-Oki earthquake occurred adjacent to the northeastern edge of the source region of the 1964 Mj 7.5 Niigata earthquake, offshore of Yamagata Prefecture, Japan. Few aftershocks occurred in the source region of the Yamagata-Oki earthquake immediately following the Niigata earthquake, and the recent seismicity rate in this region is low compared with the source region of the Niigata earthquake. This spatial variation in seismicity may allow us to elucidate plausible physical processes that shape the spatiotemporal evolution of these shallow-crustal environments. Here, we investigate the spatial variations in seismicity characteristics by applying the HIerarchical Space–Time Epidemic Type Aftershock Sequence (HIST-ETAS) model to an earthquake catalog compiled by the Japan Meteorological Agency for events in and around the Yamagata-Oki earthquake rupture region. We compare spatial variations in the background seismicity rate and aftershock productivity estimated from the HIST-ETAS model with the geophysical features in the study region. The background seismicity rate is high along the eastern margin of the Sea of Japan and correlates well with a previously identified zone that possesses a high geodetic E-W strain rate. The two major earthquakes occurred in and around a high E-W strain rate zone, suggesting that the background seismicity rate may serve as a key parameter for evaluating seismic hazard across the Japanese Archipelago. Furthermore, the source region of the Yamagata-Oki earthquake has a higher aftershock productivity and lower seismic-wave velocity than that of the Niigata earthquake. We interpret this low-velocity zone to be a well-developed damaged rock that resulted in an increase in aftershock productivity based on previous laboratory experiments and numerical results; this damage makes the rock more ductile at the macroscopic scale. The higher ductility in the source region of the Yamagata-Oki earthquake may have worked as a barrier against the propagation of dynamic rupture that occurred during the Niigata earthquake.

scholarly journals Investigating the earthquake catalog of the National Observatory of Athens

2009 ◽  
Vol 9 (3) ◽  
pp. 905-912 ◽  
Author(s):  
G. Chouliaras
Keyword(s):  
B Value ◽  
Spatial And Temporal Variability ◽  
Earthquake Catalog ◽  
National Observatory ◽  
Data Set ◽  
Seismicity Rate ◽  
Earthquake Prediction Research ◽  
The Times ◽  
Seismicity Rate Changes ◽  
Selection Of

Abstract. The earthquake catalog of the National Observatory of Athens (NOA) since the beginning of the Greek National Seismological Network development in 1964, is compiled and analyzed in this study. The b-value and the spatial and temporal variability of the magnitude of completeness of the catalog is determined together with the times of significant seismicity rate changes. It is well known that man made inhomogeneities and artifacts exist in earthquake catalogs that are produced by changing seismological networks and in this study the chronological order of periods of network expansion, instrumental upgrades and practice and procedures changes at NOA are reported. The earthquake catalog of NOA is the most detailed data set available for the Greek area and the results of this study may be employed for the selection of trustworthy parts of the data in earthquake prediction research.

scholarly journals Strong foreshock signal preceding the L'Aquila (Italy) earthquake (<i>M</i><sub>w</sub> 6.3) of 6 April 2009

2010 ◽  
Vol 10 (1) ◽  
pp. 19-24 ◽  
Author(s):  
G. A. Papadopoulos ◽  
M. Charalampakis ◽  
A. Fokaefs ◽  
G. Minadakis
Keyword(s):  
Hanging Wall ◽  
B Value ◽  
Aftershock Sequence ◽  
Earthquake Catalogue ◽  
Seismicity Rate ◽  
Background Seismicity ◽  
Before And After ◽  
Spatially Distributed ◽  
Drastic Increase ◽  
Seismogenic Area

Abstract. We used the earthquake catalogue of INGV extending from 1 January 2006 to 30 June 2009 to detect significant changes before and after the 6 April 2009 L'Aquila mainshock (Mw=6.3) in the seismicity rate, r (events/day), and in b-value. The statistical z-test and Utsu-test were applied to identify significant changes. From the beginning of 2006 up to the end of October 2008 the activity was relatively stable and remained in the state of background seismicity (r=1.14, b=1.09). From 28 October 2008 up to 26 March 2009, r increased significantly to 2.52 indicating weak foreshock sequence; the b-value did not changed significantly. The weak foreshock sequence was spatially distributed within the entire seismogenic area. In the last 10 days before the mainshock, strong foreshock signal became evident in space (dense epicenter concentration in the hanging-wall of the Paganica fault), in time (drastic increase of r to 21.70 events/day) and in size (b-value dropped significantly to 0.68). The significantly high seismicity rate and the low b-value in the entire foreshock sequence make a substantial difference from the background seismicity. Also, the b-value of the strong foreshock stage (last 10 days before mainshock) was significantly lower than that in the aftershock sequence. Our results indicate the important value of the foreshock sequences for the prediction of the mainshock.

scholarly journals Box Counting Fractal Dimension and Frequency Size Distributon of Earthquakes in the Central Himalaya Region

2021 ◽  
Vol 26 (2) ◽  
pp. 127-136
Author(s):  
Ram Krishna Tiwari ◽  
Harihar Paudyal
Keyword(s):  
Fractal Dimension ◽  
High Stress ◽  
High Strength ◽  
B Value ◽  
Earthquake Catalog ◽  
Central Himalaya ◽  
Study Region ◽  
B Values ◽  
Box Counting ◽  
Earthquake Distribution

To establish the relations between b-value and fractal dimension (D0) for the earthquake distribution, we study the regional variations of those parameters in the central Himalaya region. The earthquake catalog of 989 events (Mc = 4.0) from 1994.01.31 to 2020.10.28 was analyzed in the study. The study region is divided into two sub-regions (I) Region A: 27.3°N -30.3°N and 80°E -84.8°E (western Nepal and vicinity) and (II) Region B: 26.4°N -28.6°N and 84.8°E -88.4°E (eastern Nepal and vicinity). The b-value observed is within the range between 0.92 to 1.02 for region A and 0.64 to 0.74 for region B showing the homogeneous nature of the variation. The seismic a-value for those regions ranges respectively between 5.385 to 6.007 and 4.565 to 5.218. The low b-values and low seismicity noted for region B may be related with less heterogeneity and high strength in the crust. The high seismicity with average b-values obtained for region A may be related with high heterogeneity and low strength in the crust. The fractal dimension ≥1.74 for region A and ≥ 1.82 for region B indicate that the earthquakes were distributed over two-dimensional embedding space. The observed correlation between D0 and b is negative for western Nepal and positive for eastern Nepal while the correlation between D0 and a/b value is just opposite for the respective regions. The findings identify both regions as high-stress regions. The results coming from the study agree with the results of the preceding works and reveal information about the local disparity of stress and change in tectonic complexity in the central Himalaya region.

Correlation between earthquake b value and VP/VS ratio in Japan

2021 ◽  
Author(s):  
Pei-Ying Wu ◽  
Sean Kuanhsiang Chen ◽  
Yih-Min Wu
Keyword(s):  
Pore Pressure ◽  
Earth Science ◽  
B Value ◽  
The Other ◽  
Japan Meteorological Agency ◽  
Likelihood Method ◽  
Earthquake Catalog ◽  
Injection Wells ◽  
B Values ◽  
Value Determination

&lt;p&gt;Earthquake b value is primarily controlled by differential stress in the crust. Pore pressure has also been reported influencing b value locally. In nature, the influence can only be observed in the subsurface crust by injection wells. It remains unclear whether the influence of pore pressure on b value can be observed in the scale of the entire crust. To this end, we assume that pore pressure increases proportionally with V&lt;sub&gt;P&lt;/sub&gt;/V&lt;sub&gt;S&lt;/sub&gt; ratio, which is derived from seismic tomography studies, to examine correlation between V&lt;sub&gt;P&lt;/sub&gt;/V&lt;sub&gt;S&lt;/sub&gt; ratio and b value. We investigated this correlation in Japan because it is one of the most earthquake-prone countries with dense seismic networks and high-quality earthquake catalogs. We used an earthquake catalog from the Japan Meteorological Agency from 1998 to 2011 Feb to calculate the b values in the inland region of Japan above the 30 km depth. The selected period is based on a stable completeness of magnitude (M&lt;sub&gt;c&lt;/sub&gt;) since 1998 and the strong clustering effects by the both 2011 Tohoku and 2016 Kumamoto earthquakes. We then calculated M&lt;sub&gt;c&lt;/sub&gt; and b value by maximum curvature method and maximum likelihood method, respectively, in the grids of 0.1 &amp;#160;0.1 &amp;#160;10 km with a radius of 30 km from the center of the grids. The b value determination requires the number of earthquakes with magnitudes greater than the M&lt;sub&gt;c &lt;/sub&gt;over 150 within the radius. For the V&lt;sub&gt;P&lt;/sub&gt;/V&lt;sub&gt;S&lt;/sub&gt; ratios, we used the latest data derived from the National Research Institute for Earth Science and Disaster Resilience, Japan, to resample them to the same grids as b values. We simply resampled the V&lt;sub&gt;P&lt;/sub&gt;/V&lt;sub&gt;S&lt;/sub&gt; ratios by either averaging them into the grids of b values, or weighting them through a triangular function to the grids center of b values in depths. We analyzed b value as a function of V&lt;sub&gt;P&lt;/sub&gt;/V&lt;sub&gt;S&lt;/sub&gt; ratio and binned the b values within every 0.01 V&lt;sub&gt;P&lt;/sub&gt;/V&lt;sub&gt;S&lt;/sub&gt; interval to calculate the means and medians for liner regressions. Our preliminarily results show that there is little correlation between entire b values and V&lt;sub&gt;P&lt;/sub&gt;/V&lt;sub&gt;S &lt;/sub&gt;ratios among different depth ranges (0-10 km, 10-20 km, 20-30 km). We observed a linear negative relation in the binned data at the 10-20 km depth, however, this relation is not likely observed in the other depths. It may imply that the influence of pore pressure on b value could vary with depths. We&amp;#8217;ll calculate the b values using entire magnitude range method and compare the results to the other localized geophysical observations.&lt;/p&gt;

scholarly journals Seismic quiescence precursor to the 1983 Nihonkai-Chubu (M 7.7) earthquake, Japan

1999 ◽  
Vol 42 (5) ◽  
Author(s):  
M. Murru ◽  
R. Console ◽  
C. Montuori
Keyword(s):  
Japan Sea ◽  
Software Tool ◽  
Seismic Quiescence ◽  
Japan Meteorological Agency ◽  
False Alarms ◽  
Earthquake Catalog ◽  
High Concentration ◽  
Seismicity Rate ◽  
Rupture Area ◽  
Main Shocks

We analyzed the seismicity of Northern Honshu-Hokkaido region using the declustered earthquake catalog compiled by the Japan Meteorological Agency (JMA), for the period between January 1970 and December 1994. Making use of the ZMAP software tool, we sought to determine whether the quiescence hypothesis is applicable to 16 main shocks (M ³ 7.0) of the JMA catalog. We found a highly significant seismic quiescence prior to the May 26, 1983 Nihonkai-Chubu, MJ 7.7, earthquake. The quiescence that preceded the event lasted more than 3.5 years, and was located in the Japan Sea, off Akita and Aomori Prefectures. It was characterized by a standard deviate Z = 7.4 (Tw = 3 years), within a volume of approximately 200 by 300 by 40 km around the hypocenter. This volume contained 16 earthquakes (M ? 3.8) during the background period which lasted more than 8 years preceding the quiescence, and none during this one. A high concentration of seismic activity exceeding 15 events per year followed the main shock before the rate returned back to the previous value. No quiescence was observed before another strong event of magnitude 7.8 which occurred on July 12, 1993, 200 km north of the former, while three quiescences with the same Z-value were observed in the same region and in the same time period, not followed by any main shocks (false alarms). The probability that the Nihonkai-Chubu earthquake correlated at random with the quiescence period is estimated as approximately 1%, based on the fraction of space-time covered by alarms. The seismicity rate variations observed before and after the 1983 Nihonkai-Chubu earthquake are similar to those observed in the rupture area of the 1980 Irpinia (Italy), M 6.9 earthquake.

Nonstationary Background Seismicity Rate and Evolution of Stress Changes in the Changning Salt Mining and Shale-Gas Hydraulic Fracturing Region, Sichuan Basin, China

2020 ◽  
Vol 91 (4) ◽  
pp. 2170-2181 ◽  
Author(s):  
Ke Jia ◽  
Shiyong Zhou ◽  
Jiancang Zhuang ◽  
Changsheng Jiang ◽  
Yicun Guo ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Shale Gas ◽  
Sichuan Basin ◽  
Inversion Method ◽  
Background Rate ◽  
Study Region ◽  
Seismicity Rate ◽  
Stress Changes ◽  
Background Seismicity ◽  
Salt Mining

Abstract The Ms 6.0 earthquake in Changning, Sichuan, China, on 17 June 2019 was the largest recorded earthquake in the stable Sichuan basin. It occurred in a complicated region with salt mining and shale gas production. Whether this earthquake is induced raises concerns among the public and the scientific community. Furthermore, the relation between this earthquake and nearby industrial activities has also been of great interest. To address these questions, we estimated the nonstationary background seismicity rate and inverted for spatiotemporal stress changes. The results show that the background rate dramatically increased after hydraulic fracturing (HF) and remained at a high level until the present. Starting in 2005, the study region experienced an accelerating stress increase, and the rates of cumulative modified Coulomb stress changes were approximately 0.11  MPa/yr from January 2005 to January 2015 and 0.24  MPa/yr from January 2015 to December 2018. The 2019 Changning earthquake produced a stress step of 0.32 MPa. A clear difference between seismicity induced by salt mine injection and by HF is documented. Our results suggest that the Changning sequence might have been induced by long-term injection for salt production. Furthermore, the seismicity-stress inversion method provides a tool for using seismicity rate changes as a stress meter to monitor human-induced seismicity.

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

2016 ◽  
Vol 59 (5) ◽  
Author(s):  
Prasanta Chingtham ◽  
Babita Sharma ◽  
Sumer Chopra ◽  
Pareshnath SinghaRoy
Keyword(s):  
Scaling Laws ◽  
Main Shock ◽  
B Value ◽  
Temporal Variations ◽  
Aftershock Sequence ◽  
Earthquake Catalog ◽  
Study Region ◽  
Nepal Himalaya ◽  
B Values ◽  
Aftershock Sequences

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.

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