Earth, Planets and Space最新文献

{"title":"Coastal tsunami prediction in Tohoku region, Japan, based on S-net observations using artificial neural network","authors":"Yuchen Wang, Kentaro Imai, Takuya Miyashita, Keisuke Ariyoshi, Narumi Takahashi, Kenji Satake","doi":"10.1186/s40623-023-01912-6","DOIUrl":"https://doi.org/10.1186/s40623-023-01912-6","url":null,"abstract":"Abstract We present a novel method for coastal tsunami prediction utilizing a denoising autoencoder (DAE) model, one of the deep learning algorithms. Our study focuses on the Tohoku coast, Japan, where dense offshore bottom pressure gauges (OBPGs), called S-net, are installed. To train the model, we generated 800 hypothetical tsunami scenarios by employing stochastic earthquake models (M7.0–8.8). We used synthetic tsunami waveforms at 44 OBPGs as input and the waveforms at four coastal tide gauges as output. Subsequently, we evaluated the model’s performance using 200 additional hypothetical and two real tsunami events: the 2016 Fukushima earthquake and 2022 Tonga volcanic tsunamis. Our DAE model demonstrated high accuracy in predicting coastal tsunami waveforms for hypothetical events, achieving an impressive quality index of approximately 90%. Furthermore, it accurately forecasted the maximum amplitude of the 2016 Fukushima tsunami, achieving a quality index of 91.4% at 15 min after the earthquake. However, the prediction of coastal waveforms for the 2022 Tonga volcanic tsunami was not satisfactory. We also assessed the impact of the forecast time window and found that it had limited effects on forecast accuracy. This suggests that our method is suitable for providing rapid forecasts soon after an earthquake occurs. Our research is the first application of an artificial neural network to tsunami prediction using real observations. In the future, we will use more tsunami scenarios for model training to enhance its robustness for different types of tsunamis. Graphical Abstract","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"68 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135197956","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Improving the accuracy of polar motion prediction using a hybrid least squares and long short-term memory model","authors":"Chenxiang Wang, Pengfei Zhang","doi":"10.1186/s40623-023-01910-8","DOIUrl":"https://doi.org/10.1186/s40623-023-01910-8","url":null,"abstract":"Abstract Earth rotation parameters (ERPs) are essential for transforming between the celestial and terrestrial reference frames, and for high-precision space navigation and positioning. Among the ERPs, polar motion (PM) is a critical parameter for analyzing and understanding the dynamic interaction between the solid Earth, atmosphere, ocean, and other geophysical fluids. Traditional methods for predicting the change in ERPs rely heavily on linear models, such as the least squares (LS) and the autoregressive (AR) model (LS + AR). However, variations in ERP partly reflect non-linear effects in the Earth system, such that the predictive accuracy of linear models is not always optimal. In this paper, long short-term memory (LSTM), a non-linear neural network, is employed to improve the prediction of ERPs. Polar motion prediction experiments in this study are conducted using the LSTM model and a hybrid method LS + LSTM model based on the IERS EOP14C04 time series. Compared with Bulletin A, the PMX and PMY prediction accuracy can reach a maximum of 33.7% and 31.9%, respectively, with the LS + LSTM model. The experimental results show that the proposed hybrid model displays a better performance in mid- and long-term (120–365 days) prediction of polar motion. Graphical Abstract","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135252735","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Monitoring of equatorial plasma bubbles using aeronautical navigation system: a feasibility study","authors":"Keisuke Hosokawa, Susumu Saito, Hiroyuki Nakata, Chien-Hung Lin, Jia-Ting Lin, Pornchai Supnithi, Ichiro Tomizawa, Jun Sakai, Toru Takahashi, Takuya Tsugawa, Michi Nishioka, Mamoru Ishii","doi":"10.1186/s40623-023-01911-7","DOIUrl":"https://doi.org/10.1186/s40623-023-01911-7","url":null,"abstract":"Abstract It has long been known that field-aligned irregularities within equatorial plasma bubbles (EPBs) can cause long-range propagation of radio waves in the VHF frequencies such as those used for TV broadcasting through the so-called forward scattering process. However, no attempt has been made to use such anomalous propagations of VHF radio waves for wide-area monitoring of EPBs. In this study, we investigated the feasibility of monitoring of EPBs using VHF radio waves used for aeronautical navigation systems such as VHF Omnidirectional radio Range (VOR). There are 370 VOR stations in the Eastern and Southeastern Asian region that can be potentially used as Tx stations for the observations of anomalous propagation. We have examined the forward scattering conditions of VHF waves using the magnetic field model and confirmed that it is possible to observe the EPB-related anomalous propagation if we set up Rx stations in Okinawa (Japan), Taiwan, and Thailand. During test observations conducted in Okinawa since 2021, no signal has been received that was clearly caused by anomalous propagation due to EPBs. This is simply because EPBs have not developed to high latitudes during the observation period due to the low solar activity. In March 2023, however, possible indications of EPB-related scattering were detected in Okinawa which implies the feasibility of observing EPBs with the current observation system. We plan to conduct pilot observations in Taiwan and Thailand in future to further evaluate the feasibility of this monitoring technique. Graphical Abstract","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"98 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135738705","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Measurement of ferric iron in Chang’e-5 impact glass beads","authors":"Lixin Gu, Yangting Lin, Yongjin Chen, Yuchen Xu, Xu Tang, Sen Hu, Ho-kwang Mao, Jinhua Li","doi":"10.1186/s40623-023-01909-1","DOIUrl":"https://doi.org/10.1186/s40623-023-01909-1","url":null,"abstract":"Abstract The lunar surface and interior are highly reducing, resulting in the virtually absence of ferric ion. However, recent studies suggest the presence of ferric iron in lunar samples, and in most cases they were found in amorphous silicates (e.g., glass beads) measured by TEM–EELS. In this work, we conducted a systematic TEM–EELS analysis on the iron valence states of Chang’e-5 impact glass beads. The Fe 3+ /ΣFe ratio of each silicate glass sample was determined from integral intensity of Fe L 3 and L 2 edge. The measurements show a positive correlation between the dwell time and Fe 3+ /ΣFe ratio, which reveals that ferric iron can be significantly produced by electron beam bombardment under routine analytical condition. The calculated Fe 3+ /ΣFe with short dwell times (≤ 20 ms) in our Chang’e-5 impact glass beads show no detectable inherent ferric iron, suggesting that the ferric iron is not ubiquitous as previously reported. It is obvious that a careful control of experiment conditions is critical to determine the inherent redox state of other beam-sensitive terrestrial and extraterrestrial samples. Graphical Abstract","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135406782","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Role of fluid on seismicity of an intra-plate earthquake zone in Western India: an electrical fingerprint from magnetotelluric study","authors":"Ujjal K. Borah, Prasanta K. Patro, Khasi Raju, K. Chinna Reddy, Narendra Babu, P. Rama Rao, N. Purnachandra Rao","doi":"10.1186/s40623-023-01905-5","DOIUrl":"https://doi.org/10.1186/s40623-023-01905-5","url":null,"abstract":"Abstract The magnetotelluric (MT) investigation carried out in Koyna Seismogenic Zone (KSZ), an intra-plate earthquake region in Western India, along an E–W profile brings out moderately conductive (~ 700–1000 Ωm) near vertical features within the very high resistive (> 20,000 Ωm) granite/granite-gneiss basement. Occurrences of these anomalous moderate conductors are corroborated with sensitivity analysis. The alignment of earthquake hypocenters along the resistive–conductive boundary signifies the moderate conductor as basement fault. The conversion of resistivity values to the ratio of seismic P- to S-wave velocity ( v p / v s ) suggests that the moderate conductivity of the fault zone (as compared to the surrounding basement) appears due to the presence of fluid in the fault zone. Geophysical evidences reveal ~ 2.5–3.6 vol% fluid in the fault zone with ~ 1.8–2.6% interconnected porosity, which migrates along the structural boundary and invades the mechanically strong basement to nucleate the brittle failure within it. The present study proposes two mechanisms for the seismicity in the Koyna region. First: the meteoric water circulation due to the loading–unloading of nearby Koyna reservoir acts as potential fluid source for this triggered seismicity, which has also been suggested by previous studies. Second: the fluid circulation due to a deep-seated source. The present MT study brings out a conductive feature below 20 km depth which is thought to be emerged due to the dehydration of amphibole bearing rocks. The fluid generated from dehydration might act as a probable source to the triggered seismicity; since the conductive feature has a linkage to the upper crust. Graphical Abstract","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"66 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135386802","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A plasma irradiation system optimized for space weathering of solar system bodies","authors":"Tomoki Kimura, Misako Otsuki, Tomohiro Kitano, Ryo Hoshino, Yusuke Nakauchi, Shunsuke Haganuma, Ryu Haganuma, Tetsuo Haganuma, Fuminori Tsuchiya, Toru Tamagawa, Asami Hayato, Jun Kimura, Naoki Terada, Hideyuki Usui, Masaki N. Nishino, Shoichiro Yokota, Yohei Miyake","doi":"10.1186/s40623-023-01900-w","DOIUrl":"https://doi.org/10.1186/s40623-023-01900-w","url":null,"abstract":"Abstract In the tenuous atmospheric bodies of our solar system, space weathering on the celestial surface is an important process for its chemical and physical evolution and ambient environment on timescales of celestial evolution. Space plasma is a dominant energy and material source for space weathering. Plasma irradiation experiment in the laboratory is an effective method for modeling space weathering driven by space plasma. However, comprehensive modeling of plasma space weathering has not yet been conducted because the capabilities of the earlier facilities were not optimized for realistic space weathering; for example, the incident electron and ion were not irradiated in the same condition. Here, we developed a plasma irradiation system, Plasma Irradiation Emulator for Celestial Environments (PIECE) of the solar system bodies, which reproduces plasma space weathering in tenuous atmospheric bodies by the electron and ion irradiations in the same condition. We successfully developed a system with high electron and ion number fluxes of $$sim 10^{13} - 10^{16} {text{ particles cm}}^{{ - {2}}} {text{s}}^{{ - {1}}}$$ <mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\"> <mml:mrow> <mml:mo>∼</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>13</mml:mn> </mml:msup> <mml:mo>-</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>16</mml:mn> </mml:msup> <mml:msup> <mml:mrow> <mml:mspace /> <mml:mtext>particles cm</mml:mtext> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:msup> <mml:mrow> <mml:mtext>s</mml:mtext> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> at any acceleration energy in the range of 1–30 keV, which leads to a fluence of e.g., $$sim 10^{18} - 10^{21} {text{ particles cm}}^{{ - {2}}} {text{s}}^{{ - {1}}}$$ <mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\"> <mml:mrow> <mml:mo>∼</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>18</mml:mn> </mml:msup> <mml:mo>-</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>21</mml:mn> </mml:msup> <mml:msup> <mml:mrow> <mml:mspace /> <mml:mtext>particles cm</mml:mtext> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:msup> <mml:mrow> <mml:mtext>s</mml:mtext> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> , with a 1-day irradiation time. This fluence corresponds to a plasma irradiation time of ~ 10 3 –10 6 years on Europa. Graphical Abstract","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135421118","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Identification of active faults and tectonic features through heat flow distribution in the Nankai Trough, Japan, based on high-resolution velocity-estimated bottom-simulating reflector depths","authors":"Shuto Takenouchi, Takeshi Tsuji, Kazuya Shiraishi, Yasuyuki Nakamura, Shuichi Kodaira, Gou Fujie, Kota Mukumoto","doi":"10.1186/s40623-023-01890-9","DOIUrl":"https://doi.org/10.1186/s40623-023-01890-9","url":null,"abstract":"Abstract Estimates of heat flow can contribute to our understanding of geological structures in plate convergent zones that produce great earthquakes. We applied automated velocity analysis to obtain the accurate seismic profiles needed for precise heat flow estimates using six new seismic profiles acquired during R/V Kaimei KM18-10 voyage in 2018. We calculated heat flow values in the accretionary wedge of the Nankai Trough off the Kii Peninsula, Japan, from the positions of widespread bottom-simulating reflectors (BSRs) in seismic reflection profiles. Calculated conductive heat flow values from the depth of the BSR agree with previous studies where a regional trend is observed from ~ 50 mW/m 2 to < 40 mW/m 2 60 km landward from the deformation front. This trend is caused by thickening of accretionary sediments and the subduction of the Philippines Sea plate. Segments of profiles are marked by anomalous high heat flow values. Such anomalies represent alterations of the shallow crustal thermal structure caused either by a combination of topographic affects, surface erosion of the seafloor, or by fluid flow that transports heat by advection. We interpret heat flow anomalies (~ 100 mW/m 2 ) as indicators of active faulting, which correspond to low seismic velocity zones along faults. Our results also showed relatively high heat flow at the landward end of several survey lines close to the Kii Peninsula, which we interpret to the possible presence of plutonic rocks that underlie the Kii Peninsula and extend offshore and may be the cause of geothermal springs, steep geothermal gradients, and high heat flow. Graphical abstract","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"70 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135817479","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characteristics and longitudinal extent of VLF quasi-periodic emissions using multi-point ground-based observations","authors":"Claudia Martinez-Calderon, Tomoka Oonishi, Kazuo Shiokawa, Jyrki K. Manninen, Alexey Oinats, Mitsunori Ozaki","doi":"10.1186/s40623-023-01898-1","DOIUrl":"https://doi.org/10.1186/s40623-023-01898-1","url":null,"abstract":"Abstract Quasi-periodic (QP) emissions are a type of magnetospheric ELF/VLF waves characterized by a periodic intensity modulation ranging from tens of seconds to several minutes. Here, we present 63 QP events observed between January 2017 and December 2018. Initially detected at the VLF receiver in Kannuslehto, Finland (KAN, MLAT = 67.7°N, L = 5.5), we proceeded to check whether these events were simultaneously observed at other subauroral receivers. To do so we used the following PWING stations: Athabasca (ATH, MLAT = 61.2°N, L = 4.3, Canada), Gakona (GAK, MLAT = 63.6°N, L = 4.9, Alaska), Husafell (HUS, MLAT = 64.9°N, L = 5.6, Iceland), Istok (IST, MLAT = 60.6°N, L = 6.0, Russia), Kapuskasing (KAP, MLAT = 58.7°N, L = 3.8, Canada), Maimaga (MAM, MLAT = 58.0°N, L = 3.6, Russia), and Nain (NAI, MLAT = 65.8°N, L = 5.0, Canada). We found that: (1) QP emissions detected at KAN had a relatively longer observation time (1–10 h) than other stations, (2) 11.3% of the emissions at KAN were observed showing one-to-one correspondence at IST, and (3) no station other than IST simultaneously observed the same QP emission as KAN. Since KAN and IST are longitudinally separated by 60.6°, we estimate that the maximum meridional spread of conjugated QP emissions should be close to 60° or 4 MLT. Comparison with geomagnetic data shows half of the events are categorized as type II, while the rest are mixed (type I and II). This study is the first to clarify the longitudinal spread of QP waves observed on the ground by analyzing simultaneous observations over 2 years using multiple ground stations. Graphical Abstract","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135816732","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On a large magmatic fluid reservoir oblique to the volcanic front in the southern part of NE Japan revealed by the magnetotelluric survey","authors":"Dieno Diba, Makoto Uyeshima, Masahiro Ichiki, Shin’ya Sakanaka, Makoto Tamura, Yiren Yuan, Marceau Gresse, Yusuke Yamaya, Yoshiya Usui","doi":"10.1186/s40623-023-01899-0","DOIUrl":"https://doi.org/10.1186/s40623-023-01899-0","url":null,"abstract":"Abstract Many active volcanoes and various types of seismic activities exist in the southern part of the Northeast Japan subduction zone. One of the geologically most interesting features in this area is the sequential explosive eruptions of a group of volcanoes. The group consists of Mt. Azuma and Mt. Adatara on the volcanic front line, Mt. Bandai west of the volcanic front, and Mt. Numazawa on the back-arc side. A previous petrological study on the eruption products regarded Mt. Numazawa as an anomalous back-arc volcano because its lavas are similar to those of volcanoes on the volcanic front. The reason behind this unique connection was unclear, and hence, this study was intended to understand the deep fluids distribution beneath the area. For this purpose, a 3-D regional electrical resistivity structure was estimated from a series of wide-band magnetotelluric surveys, with 45 observation points deployed from the fore-arc to the back-arc sides. The most important feature of the resistivity structure is a large conductive zone in the central part of the area, spanning from the upper mantle to the lower crust. Interestingly, the lateral elongation of the conductor is oblique to the volcanic front line and consistent with the spatial distribution of the group of volcanoes and the low-frequency earthquake clusters around them. Therefore, the conductor most likely represents a large, elongated magmatic fluid reservoir beneath the volcanoes. Hydrous partial melting might be the cause of the enhanced conductivity. Graphical Abstract","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135817633","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Postseismic gravity changes after the 2011 Tohoku earthquake observed by superconducting gravimeters at Mizusawa, Japan","authors":"Yoshiaki Tamura, Takahito Kazama, Ryuichi Nishiyama, Koji Matsuo, Yuichi Imanishi","doi":"10.1186/s40623-023-01901-9","DOIUrl":"https://doi.org/10.1186/s40623-023-01901-9","url":null,"abstract":"Abstract Postseismic gravity changes after the 2011 Tohoku earthquake (Mw9.0) were investigated using the data from superconducting gravimeters (SGs) at Mizusawa, Japan. The data in the period from 2014 to 2021 were used in the analysis. The SG data were first corrected for instrumental drift using the results of absolute gravity measurements. Then, correction for the hydrological effect was applied based on physical modeling of soil moisture. Finally, the effect of vertical displacement of the station (free-air effect) was corrected using GNSS data. After these corrections, residual gravity indicated a long-term increase, with its rate gradually decreasing with time. This fact suggests that viscoelastic relaxation after the earthquake played an important role in producing the long-term gravity changes. Fitting a decaying exponential function of time to the residual series yielded 89.4 ± 4.4 µGal (1 µGal = 10 –8 ms –2 ) as the total gravity change and 635 ± 17 days as the characteristic time scale. In addition to the ground-based observations, the data from satellite gravity missions GRACE/GRACE-FO were analyzed to retrieve gravity changes at Mizusawa. Similar analysis of the satellite-based data yielded 15.2 ± 1.6 µGal as the total gravity change and 3444 ± 599 days as the characteristic time scale. The difference in the estimates of the total gravity change, of a factor of about 6, from the ground-based and the satellite-based observations may be attributed to the limited spatial resolution in the latter method. The difference in the estimates of the time scale, of a factor of about 1/5, may originate from the difference in the depth where the two kinds of gravimetry are mainly sensitive. Referring to recent theoretical studies on postseismic deformations after the 2011 Tohoku earthquake, our results can be interpreted consistently by assuming the existence of a layer of viscoelastic materials with viscosity $$2times {10}^{18} text{Pa s}$$ <mml:math xmlns:mml=\"http://www.w3.org/1998/Math/MathML\"> <mml:mrow> <mml:mn>2</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mn>18</mml:mn> </mml:msup> <mml:mtext>Pa s</mml:mtext> </mml:mrow> </mml:math> underneath the Tohoku area of Japan. Graphical Abstract","PeriodicalId":11409,"journal":{"name":"Earth, Planets and Space","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136235753","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}