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Kenji Satake - One of the best experts on this subject based on the ideXlab platform.
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waveform and spectral analyses of the 2011 japan tsunami records on Tide Gauge and dart stations across the pacific ocean
Pure and Applied Geophysics, 2013Co-Authors: Mohammad Heidarzadeh, Kenji SatakeAbstract:We studied the 11 March 2011 Tohoku tsunami through analysis of the sea level records from 21 Tide Gauge and 16 DART (Deep-ocean Assessment and Reporting of Tsunamis) stations from across the Pacific Ocean. The extreme power of this trans-oceanic tsunami was indicated by the trough-to-crest heights of 3.03 m at Arena Cove on the western coast of the USA and 3.94 m at Coquimbo on the southern coast of Chile. The average value of the maximum amplitude was 163.9 cm for the examined Tide Gauge records. At many coastal Tide Gauge stations the largest wave arrived several hours after the first arrival of the tsunami wave, and the tsunami lasted for a long time with an average duration of 4 days. On the contrary, at most of the DART stations in the deep ocean, the first wave was the largest, the tsunami amplitudes were smaller with an average maximum of 51.2 cm, and the durations were shorter with an average of 2 days. The two dominant tsunami periods on the DART records were 37 and 67.4 min, which are possibly attributed to the width and length of the tsunami source fault, respectively. The dimensions of the tsunami source was estimated as 233 km × 424 km. Wavelet analyses of Tide Gauge and DART records showed that most of the tsunami energy was distributed at the wide period band of around 10–80 min during the first hour after the tsunami arrival, then it was concentrated in a relatively narrower band. The frequency-time plots showed the switches and lapses of tsunami energy at the 35- and 65-min period bands.
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in situ measurements of Tide Gauge response and corrections of tsunami waveforms from the niigataken chuetsu oki earthquake in 2007
Pure and Applied Geophysics, 2009Co-Authors: Yuichi Namegaya, Yuichiro Tanioka, Kuniaki Abe, Kenji Satake, K Hirata, Masami Okada, Aditya Riadi GusmaAbstract:Linear and nonlinear responses of ten well-type Tide Gauge stations on the Japan Sea coast of central Japan were estimated by in situ measurements. We poured water into the well or drained water from the well by using a pump to make an artificial water level difference between the outer sea and the well, then measured the recovery of water level in the well. At three Tide Gauge stations, Awashima, Iwafune, and Himekawa, the sea-level change of the outer sea is transmitted to the Tide well instantaneously. However, at seven Tide Gauge stations, Nezugaseki, Ryotsu, Ogi, Teradomari, Banjin, Kujiranami, and Naoetsu, the sea-level change of the outer sea is not always transmitted to the Tide well instantaneously. At these stations, the recorded tsunami waveforms are not assured to follow the actual tsunami waveforms. Tsunami waveforms from the Niigataken Chuetsu-oki Earthquake in 2007 recorded at these stations were corrected by using the measured Tide Gauge responses. The corrected amplitudes of the first and second waves were larger than the uncorrected ones, and the corrected peaks are a few minutes earlier than the uncorrected ones at Banjin, Kujiranami, and Ogi. At Banjin, the correction was significant; the corrected amplitudes of the first and second upward motion are +103 cm and +114 cm, respectively, while the uncorrected amplitudes were +96 cm and +88 cm. At other Tide Gauge stations, the differences between the uncorrected and corrected tsunami waveforms were insignificant.
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tsunami source of the 2004 sumatra andaman earthquake inferred from Tide Gauge and satellite data
Bulletin of the Seismological Society of America, 2007Co-Authors: Yushiro Fujii, Kenji SatakeAbstract:Tsunami source of the 2004 Sumatra-Andaman earthquake was esti- mated from a joint inversion of tsunami waveforms recorded on Tide Gauges and sea surface heights captured by satellite altimetry measurements. The earthquake, the largest in the past 40 years, caused devastating tsunami damage to countries around the Indian Ocean, but the tsunami source, in particular, its northern end, was not well resolved. Although aftershocks and crustal deformation extended from off north- western Sumatra Island through the Nicobar Islands to the Andaman Islands, some seismic-wave analyses indicated a shorter source length, several hundred kilometers. We used tsunami waveforms recorded at 12 Tide Gauge stations around the source and the sea surface heights measured by three satellites: Jason1, TOPEX/Poseidon, and Envisat. We numerically computed tsunami propagation using realistic bathym- etry; more than 66,000 depth points were digitized from nautical charts and combined with the ETOPO2 data. Inversion of satellite data indicates that the tsunami source extended to the Andaman Islands with a total length of 1,400 km, but such a model produces much larger tsunami waveforms than observed at Indian Tide Gauge stations. Inversion of Tide Gauge records and the joint inversion indicate that the tsunami source was about 900 km long. The largest slip, about 13 to 25 m, was located off Sumatra Island and the second largest slip, up to 7 m, near the Nicobar Islands. The slip distribution is similar for different rupture velocities and rise times, with a slow velocity of 1 km/sec and a rise time of 3 min yielding the largest variance reduction.
Thomas Frederikse - One of the best experts on this subject based on the ideXlab platform.
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a comparison of methods to estimate vertical land motion trends from gnss and altimetry at Tide Gauge stations
Ocean Science, 2018Co-Authors: Marcel Kleinherenbrink, Riccardo Riva, Thomas FrederikseAbstract:Abstract. Tide Gauge (TG) records are affected by vertical land motion (VLM), causing them to observe relative instead of geocentric sea level. VLM can be estimated from global navigation satellite system (GNSS) time series, but only a few TGs are equipped with a GNSS receiver. Hence, (multiple) neighboring GNSS stations can be used to estimate VLM at the TG. This study compares eight approaches to estimate VLM trends at 570 TG stations using GNSS by taking into account all GNSS trends with an uncertainty smaller than 1 mm yr−1 within 50 km. The range between the methods is comparable with the formal uncertainties of the GNSS trends. Taking the median of the surrounding GNSS trends shows the best agreement with differenced altimetry–Tide Gauge (ALT–TG) trends. An attempt is also made to improve VLM trends from ALT–TG time series. Only using highly correlated along-track altimetry and TG time series reduces the SD of ALT–TG time series by up to 10 %. As a result, there are spatially coherent changes in the trends, but the reduction in the root mean square (RMS) of differences between ALT–TG and GNSS trends is insignificant. However, setting correlation thresholds also acts like a filter to remove problematic TG time series. This results in sets of ALT–TG VLM trends at 344–663 TG locations, depending on the correlation threshold. Compared to other studies, we decrease the RMS of differences between GNSS and ALT–TG trends (from 1.47 to 1.22 mm yr−1), while we increase the number of locations (from 109 to 155), Depending on the methods the mean of differences between ALT–TG and GNSS trends vary between 0.1 and 0.2 mm yr−1. We reduce the mean of the differences by taking into account the effect of elastic deformation due to present-day mass redistribution. At varying ALT–TG correlation thresholds, we provide new sets of trends for 759 to 939 different TG stations. If both GNSS and ALT–TG trend estimates are available, we recommend using the GNSS trend estimates because residual ocean signals might correlate over long distances. However, if large discrepancies ( > 3 mm yr−1) between the two methods are present, local VLM differences between the TG and the GNSS station are likely the culprit and therefore it is better to take the ALT–TG trend estimate. GNSS estimates for which only a single GNSS station and no ALT–TG estimate are available might still require some inspection before they are used in sea level studies.
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estimating decadal variability in sea level from Tide Gauge records an application to the north sea
Journal of Geophysical Research, 2016Co-Authors: Thomas Frederikse, Riccardo Riva, Cornelis Slobbe, T Oerse, Marti VerlaaAbstract:One of the primary observational data sets of sea level is represented by the Tide Gauge record. We propose a new method to estimate variability on decadal time scales from Tide Gauge data by using a state space formulation, which couples the direct observations to a predefined state space model by using a Kalman filter. The model consists of a time-varying trend and seasonal cycle, and variability induced by several physical processes, such as wind, atmospheric pressure changes and teleconnection patterns. This model has two advantages over the classical least-squares method that uses regression to explain variations due to known processes: a seasonal cycle with time-varying phase and amplitude can be estimated, and the trend is allowed to vary over time. This time-varying trend consists of a secular trend and low-frequency variability that is not explained by any other term in the model. As a test case, we have used Tide Gauge data from stations around the North Sea over the period 1980–2013. We compare a model that only estimates a trend with two models that also remove intra-annual variability: one by means of time series of wind stress and sea level pressure, and one by using a two-dimensional hydrodynamic model. The last two models explain a large part of the variability, which significantly improves the accuracy of the estimated time-varying trend. The best results are obtained with the hydrodynamic model. We find a consistent low-frequency sea level signal in the North Sea, which can be linked to a steric signal over the northeastern part of the Atlantic.
Jerry X Mitrovica - One of the best experts on this subject based on the ideXlab platform.
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glacial isostatic adjustment in 3 d earth models implications for the analysis of Tide Gauge records along the u s east coast
Journal of Geodynamics, 2008Co-Authors: Jonatha E Davis, Jerry X Mitrovica, Konstanti Latychev, Robly A Kendall, Mark E TamisieaAbstract:Abstract Tide Gauge records of recent sea-level change along the U.S. east coast have received significant attention within the literature of glacial isostatic adjustment (GIA). Geographic trends in these Tide Gauge rates are not reduced by a GIA correction based on a commonly adopted radial viscosity profile (characterized, in particular, by a lower mantle viscosity ∼ 1 − 2 × 1 0 21 Pa s), and this has led to speculation that the residual trends reflect contributions from neotectonics or oceanographic processes. While the trends can be significantly reduced by adopting an Earth model with a stiffer lower mantle, such a model appears to be incompatible with independent constraints from post-glacial decay times in Hudson Bay. We use a finite-element model of the GIA process to investigate whether 3-D viscosity variations superimposed onto the “common” radial viscosity profile may provide a route to reconciling the east coast sea-level trends. We find that the specific 3-D structure we impose has little impact on the geographic trends in the GIA-corrected rates. However, we do find that the imposed lateral variations in lower mantle viscosity introduce a nearly uniform upward shift of 0.5 mm/yr in GIA-induced sea-level rates along the U.S. east coast. Thus, inferences of regional (U.S. east coast) sea-level rise due to modern melting of ice reservoirs, based on Tide Gauge rates corrected using 1-D GIA models, may be significantly biased by this simplifying assumption.
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decontaminating Tide Gauge records for the influence of glacial isostatic adjustment the potential impact of 3 d earth structure
Geophysical Research Letters, 2006Co-Authors: Robly A Kendall, Jerry X Mitrovica, Jonatha E Davis, Konstanti Latychev, Mark E TamisieaAbstract:[1] We investigate the potential impact of lateral variations in mantle viscosity and lithospheric thickness on predictions of present-day relative sea-level change due to glacial isostatic adjustment (GIA). We consider three viscoelastic Earth models. The first is a 1-D model with a lithospheric thickness of 120 km and upper and lower mantle viscosities of 5 × 1020 Pa s and 5 × 1021 Pa s, respectively. The second model includes global lithospheric thickness variations and lateral heterogeneities in upper mantle viscosity ranging over three orders of magnitude, while the third model includes lateral variations in lower mantle viscosity alone. We find that the impact of 3-D structure is significant. Indeed, the difference between the 3-D and 1-D model predictions at ∼300 sites with Tide Gauge records longer than 40 years duration is greater than 0.2 mm/yr and 0.5 mm/yr for 50% and 25% of the sites, respectively. The maximum difference exceeds several mm/yr. We conclude that efforts to decontaminate Tide Gauge records for ongoing GIA, to determine the rate and origin of global sea-level rise, should incorporate 3-D mantle structure into the GIA modelling.
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vertical crustal motion determined by satellite altimetry and Tide Gauge data in fennoscandia
Geophysical Research Letters, 2004Co-Authors: Chungye Kuo, C K Shum, Jerry X MitrovicaAbstract:[1] We present a new method of combining satellite altimetry and Tide Gauge data to obtain improved estimates of absolute (or geocentric) vertical crustal motion at Tide Gauges within a semi-enclosed sea. As an illustration, we combine TOPEX/POSEIDON altimetry data (1992-2001) and 25 long-term (>40 years) Tide Gauge records around the Baltic Sea region of Fennoscandia, an area where crustal deformation is dominated by glacial isostatic adjustment (GIA). A comparison of the estimated vertical motion, at 1-11 mm/yr, with independent solutions from 10 collocated BIFROST GPS sites, shows a difference of 0.2 ± 0.9 mm/yr, thus verifying the accuracy and robustness of the procedure. The solution uncertainty is estimated at 0.4 mm/yr, which is significantly lower than previous analyses of this type. We conclude that our technique can potentially provide accurate vertical motion observations globally where long-term Tide Gauge records exist.
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glacial isostatic adjustment and the anomalous Tide Gauge record of eastern north america
Nature, 1996Co-Authors: J L Davis, Jerry X MitrovicaAbstract:SEA-LEVEL variations, as recorded by the global network of Tide Gauges, represent a rich data set for studying a wide range of natural and anthropogenic phenomena, such as the sea-level rise induced by possible global warming. For this purpose, long-term sea-level trends must be corrected for the 'contaminating' effects of continuing glacial isostatic adjustment1–5 (GIA). The numerical correction procedure has, for sites on the east coast of North America, yielded a set of highly anomalous sea-level rates characterized by systematic geographical trends2,4,5. We demonstrate that these trends are a consequence of inadequacies in the previous 'standard' numerical prediction for GIA. In particular, we find that the well-known trends in the GIA-corrected Tide Gauge rates are eliminated if the lower-mantle viscosity of the Earth model used in the GIA prediction is increased. This result obviates the need to explain the anomalous trend as a manifestation of Gulf Stream ocean circulation4 or neotectonic processes2.
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present day post glacial sea level change far from the late pleistocene ice sheets implications for recent analyses of Tide Gauge records
Geophysical Research Letters, 1995Co-Authors: Jerry X Mitrovica, J L DavisAbstract:We examine the sensitivity of predictions of the present-day rate of sea level change due to glacial isostatic adjustment (GIA) in two regions located within the ‘far-field’ of the Late Pleistocene ice sheets (Europe/north Africa and the western Pacific/Caribbean) to variations in the mantle viscosity profile. The regions considered here encompass the location of 11 (of 21) sites used in a recent determination, based on GIA-corrected Tide Gauge records, of the global rate of secular sea level change. Our analysis suggests that the mean GIA correction at the 11 far-field sites may vary by as much as 0.5 mm/yr, depending on the adopted Earth model, and we derive a bound on the (residual) secular sea level rise of 1.1 to 1.6 mm/yr. This bound is consistent with our analysis of the Tide Gauge record from the U.S. east coast, and it suggests that previous estimates of the residual sea level rise represent an upper bound.
Riccardo Riva - One of the best experts on this subject based on the ideXlab platform.
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a comparison of methods to estimate vertical land motion trends from gnss and altimetry at Tide Gauge stations
Ocean Science, 2018Co-Authors: Marcel Kleinherenbrink, Riccardo Riva, Thomas FrederikseAbstract:Abstract. Tide Gauge (TG) records are affected by vertical land motion (VLM), causing them to observe relative instead of geocentric sea level. VLM can be estimated from global navigation satellite system (GNSS) time series, but only a few TGs are equipped with a GNSS receiver. Hence, (multiple) neighboring GNSS stations can be used to estimate VLM at the TG. This study compares eight approaches to estimate VLM trends at 570 TG stations using GNSS by taking into account all GNSS trends with an uncertainty smaller than 1 mm yr−1 within 50 km. The range between the methods is comparable with the formal uncertainties of the GNSS trends. Taking the median of the surrounding GNSS trends shows the best agreement with differenced altimetry–Tide Gauge (ALT–TG) trends. An attempt is also made to improve VLM trends from ALT–TG time series. Only using highly correlated along-track altimetry and TG time series reduces the SD of ALT–TG time series by up to 10 %. As a result, there are spatially coherent changes in the trends, but the reduction in the root mean square (RMS) of differences between ALT–TG and GNSS trends is insignificant. However, setting correlation thresholds also acts like a filter to remove problematic TG time series. This results in sets of ALT–TG VLM trends at 344–663 TG locations, depending on the correlation threshold. Compared to other studies, we decrease the RMS of differences between GNSS and ALT–TG trends (from 1.47 to 1.22 mm yr−1), while we increase the number of locations (from 109 to 155), Depending on the methods the mean of differences between ALT–TG and GNSS trends vary between 0.1 and 0.2 mm yr−1. We reduce the mean of the differences by taking into account the effect of elastic deformation due to present-day mass redistribution. At varying ALT–TG correlation thresholds, we provide new sets of trends for 759 to 939 different TG stations. If both GNSS and ALT–TG trend estimates are available, we recommend using the GNSS trend estimates because residual ocean signals might correlate over long distances. However, if large discrepancies ( > 3 mm yr−1) between the two methods are present, local VLM differences between the TG and the GNSS station are likely the culprit and therefore it is better to take the ALT–TG trend estimate. GNSS estimates for which only a single GNSS station and no ALT–TG estimate are available might still require some inspection before they are used in sea level studies.
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estimating decadal variability in sea level from Tide Gauge records an application to the north sea
Journal of Geophysical Research, 2016Co-Authors: Thomas Frederikse, Riccardo Riva, Cornelis Slobbe, T Oerse, Marti VerlaaAbstract:One of the primary observational data sets of sea level is represented by the Tide Gauge record. We propose a new method to estimate variability on decadal time scales from Tide Gauge data by using a state space formulation, which couples the direct observations to a predefined state space model by using a Kalman filter. The model consists of a time-varying trend and seasonal cycle, and variability induced by several physical processes, such as wind, atmospheric pressure changes and teleconnection patterns. This model has two advantages over the classical least-squares method that uses regression to explain variations due to known processes: a seasonal cycle with time-varying phase and amplitude can be estimated, and the trend is allowed to vary over time. This time-varying trend consists of a secular trend and low-frequency variability that is not explained by any other term in the model. As a test case, we have used Tide Gauge data from stations around the North Sea over the period 1980–2013. We compare a model that only estimates a trend with two models that also remove intra-annual variability: one by means of time series of wind stress and sea level pressure, and one by using a two-dimensional hydrodynamic model. The last two models explain a large part of the variability, which significantly improves the accuracy of the estimated time-varying trend. The best results are obtained with the hydrodynamic model. We find a consistent low-frequency sea level signal in the North Sea, which can be linked to a steric signal over the northeastern part of the Atlantic.
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regional biases in absolute sea level estimates from Tide Gauge data due to residual unmodeled vertical land movement
Geophysical Research Letters, 2012Co-Authors: Ma A King, Maxim Keshi, Pippa L Whitehouse, Ia D Thomas, Gle A Milne, Riccardo RivaAbstract:The only vertical land movement signal routinely corrected for when estimating absolute sea-level change from Tide Gauge data is that due to glacial isostatic adjustment (GIA). We compare modeled GIA uplift (ICE-5G + VM2) with vertical land movement at ?300 GPS stations located near to a global set of Tide Gauges, and find regionally coherent differences of commonly ±0.5–2 mm/yr. Reference frame differences and signal due to present-day mass trends cannot reconcile these differences. We examine sensitivity to the GIA Earth model by fitting to a subset of the GPS velocities and find substantial regional sensitivity, but no single Earth model is able to reduce the disagreement in all regions. We suggest errors in ice history and neglected lateral Earth structure dominate model-data differences, and urge caution in the use of modeled GIA uplift alone when interpreting regional- and global- scale absolute (geocentric) sea level from Tide Gauge data.
Gary T Mitchum - One of the best experts on this subject based on the ideXlab platform.
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an improved calibration of satellite altimetric heights using Tide Gauge sea levels with adjustment for land motion
Marine Geodesy, 2000Co-Authors: Gary T MitchumAbstract:Several major improvements to an existing method for calibrating satellite altimeters using Tide Gauge data are described. The calibration is in the sense of monitoring and correcting temporal drift in the altimetric time series, which is essential in efforts to use the altimetric data for especially demanding applications. Examples include the determination of the rate of change of global mean sea level and the study of the relatively subtle, but climatically important, decadal variations in basin scale sea levels. The improvements are to the method described by Mitchum (1998a), and the modifications are of two basic types. First, since the method depends on the cancellation of true ocean signals by differencing the altimetric data from the Tide Gauge sea level time series, improvements are made that produce a more complete removal of the ocean signals that comprise the noise for the altimetric drift estimation problem. Second, a major error source in the Tide Gauge data, namely land motion, is explicitl...
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comparison of topex sea surface heights and Tide Gauge sea levels
Journal of Geophysical Research, 1994Co-Authors: Gary T MitchumAbstract:TOPEX sea surface height data from the first 300 days of the mission are compared to sea level data from 71 Tide Gauges. The initial comparison uses sea surface height data processed according to standard procedures as defined in the users handbook. It is found that the median correlations for island and for coastal Tide Gauges are 0.53 and 0.42, respectively. The analogous RMS differences between the two data sets are 7.9 and 10.4 cm. The comparisons improve significantly when a 60-day harmonic is fit to the differences and removed. This period captures aliased M2 and S2 tidal energy that is not removed by the Tide model. Making this correction and smoothing the sea surface height data over 25-km along-track segments results in median correlations of 0.58 and 0.46 for the islands and coastal stations, and median RMS differences of 5.8 and 7.7 cm, respectively. Removing once per revolution signals from the sea surface heights results in degraded comparisons with the sea levels. It is also found that a number of stations have poor comparisons due to propagating signals that introduce temporal lags between the altimeter and Tide Gauge time series. A final comparison is made by eliminating stations where this propagation effect is large, discarding two stations that are suspected to have problems with the sea level data, smoothing over 10-day intervals, and restricting attention to island Gauges. This results in a set of 552 data pairs that have a correlation of 0.66 and a RMS difference of 4.3 cm. The conclusion is that on timescales longer than about 10 days the RMS sea surface height errors are less than or of the order of several centimeters.
