We show the feasibility of a real‐time estimation of waveforms and coseismic displacements, within a few centimeters in accuracy, with a stand‐alone dual‐frequency Global Positioning System (GPS) ...receiver using a so‐called “variometric” approach. The approach is based on time single‐differences of carrier phase observations collected at a high‐rate (1 Hz or more) using a stand‐alone receiver, and on standard GPS broadcast products (orbits and clocks), which are ancillary information routinely available in real time. In the approach, first, the time series of epoch‐by‐epoch displacements are estimated. Then, provided that the collected observations are continuous, they can be summed over the interval (limited to a few minutes) over which an earthquake occurs. Since epoch‐by‐epoch displacements divided by the interval between consecutive epochs are essentially equal to the epoch‐by‐epoch velocities, this is equivalent to saying that we are using the GPS receiver as a velocimeter. Estimation biases, due to the possible mismodeling of various intervening effects (such as multipath, residual clock errors, orbit errors, and atmospheric errors), accumulate over time and display their signature as a trend in coseismic displacements. The trend can be considered linear and easily removed, at least for short intervals. Since the proposed approach (named VADASE (Variometric Approach for Displacements Analysis Stand‐alone Engine)) does not require either additional technological complexity or a centralized data analysis, in principle it can be embedded into GPS receiver firmware, thereby providing a significant contribution to tsunami warning and other hazard assessment systems. After a preliminary test using a simulated example, the effectiveness of this approach was proven using real data. We analyzed the 1 Hz GPS data recorded by the International Global Navigation Satellite Systems Service station BREW during the Denali Fault, Alaska, earthquake (Mw 7.9, 3 November, 2002, 22:12:41 UTC), as well as the 5 Hz data collected by some of the stations of the University NAVSTAR Consortium‐Plate Boundary Observatory network and the California Real Time Network during the Baja California, Mexico, earthquake (Mw 7.2, 4 April, 2010, 22:40:42 UTC). Comparisons of the results obtained using VADASE, as well as other already well‐established approaches, displayed agreement to within a few centimeters.
Key Points
RT GPS‐based coseismic displacements estimation at few cm accuracy is shown
The proposed strategy can be embedded in the GPS receiver firmware
It is useful for RT earthquakes source modeling and tsunami early‐warning system
Here, we present the application to the great Tohoku-oki (Japan) earthquake (United States Geological Survey M = 9.0, March 11, 2011, 05:46:24 Coordinated Universal Time) of a novel approach, named ...Variometric Approach for Displacements Analysis Stand-Alone Engine, able to estimate accurate coseismic displacements and waveforms in real time, in the global reference frame, just using the standard broadcast products (orbits and clocks) and the high-rate (1 Hz or more) carrier phase observations continuously collected by a stand-alone global-positioning-system receiver. We processed separately the data collected at MIZU (Mizusawa, 140 km from the epicenter) and USUD (Usuda, 430 km from the epicenter) International Global Navigation Satellite System Service sites. A total horizontal displacement of about 2.4 m east-southeast was estimated for the MIZU, with a maximum horizontal oscillation amplitude of about 3.4 m along the same direction. Generally, an overall accuracy better than 10 cm for all the components (east, north, and up) and an average accuracy around 5 cm were assessed over an interval shorter than 5 min, with respect to independent solutions obtained with two different scientific software. The threshold of 5-cm accuracy has been recently indicated as sufficient for real-time fault determination for near-field tsunami forecasting for a major earthquake, like the 2011 Tohoku-oki one.
The variometric approach to real-time high-frequency geodesy Fratarcangeli, F.; Ravanelli, M.; Mazzoni, A. ...
Atti della Accademia nazionale dei Lincei. Rendiconti Lincei. Scienze fisiche e naturali,
06/2018, Letnik:
29, Številka:
Suppl 1
Journal Article
Recenzirano
High-frequency geodesy is here intended as the capability of retrieving information relevant to geodesy and geophysics at high frequency through geodetic measurements and methodologies. In ...particular, this short review work focuses on two aspects: fast ground motions, as those due to earthquakes, and fast ionospheric total electron content (TEC) disturbances, as those caused by tsunamis. This information can be retrieved, even in real time, from Global Navigation Satellite System observations collected at high rate (equal or higher than 1 Hz), and can significantly support geohazard understanding contributing in seismic moment estimation and tsunami early warning. Here, the real-time possibilities of the new variometric approach for high-frequency geodesy are summarized: the fundamental idea is to directly focus on the quantities of interest, which are “variations” (of positions, of ionospheric TEC) and can be properly estimated in real time. The work moves “from ground to ionosphere”: with respect to the ground, the more consolidated application of the variometric approach to GNSS seismology (VADASE) is presented, up to the latest developments; with respect to the ionosphere, the brand new application named VARION for TEC disturbances computation is described, and the first results of the application to the Illapel, Chile earthquake (USGS
M
=
8.3
, 16 September 2015, 22:54:32 UTC) are shown.
Exposure to environmental tobacco smoke (ETS) was assessed as part of a pilot study aimed at determining the extent of multiple
toxicant exposures in children from inner-city areas of Baltimore, MD. ...Questionnaire data on sources of ETS and urinary cotinine
were obtained in children considered at high risk for urban exposures because of previous or current overexposure to one inner-city
environmental hazard, lead. Fifty-three (67.1%) of the 79 participants were exposed to ETS in the preceding 48 h as assessed
by questionnaire. Cotinine was present in 77 (98.7%) of the 78 samples assayed with a mean of 79.2 ng/mg creatinine (54.7
ng/ml). Eighty % of children had cotinine values > or = 30 ng/mg creatinine, a level commonly associated with household ETS
exposure. Levels in children without reported ETS exposure in their homes were also elevated (mean = 45.0 ng/mg creatinine).
As expected, blood lead levels were elevated with a mean of 23.6 micrograms/dl. We conclude that these inner-city children
have substantial exposures to both ETS and lead. Furthermore, the presence of elevated cotinine levels in children without
known household exposure suggests that ETS should be considered an urban toxicant as well as an individual residential exposure.
Biochemical validation of reported exposure to environmental tobacco smoke (ETS) lends credibility to epidemiological studies investigating the association of passive inhalation of smoke to ...respiratory disease or lung cancer. In the current study, a series of questions regarding ETS exposure was self-administered to nonsmokers and self-reported intensity of exposure was compared with cotinine levels in urine samples obtained on site. The target population of this study was a group of municipal workers who reported exposure in a domestic setting and/or in the workplace. When asked if they were exposed to ETS on social occasions, both males and females who responded positively had higher urinary cotinine levels (P less than 0.02) than those who gave a negative response. Mean urinary cotinine concentrations were found to be elevated in both men and women who reported that they lived with a smoker. Cotinine levels in the urine of those reporting exposure were over twice as high as those in the urine of respondents who denied having been exposed. ETS exposure in the home was the greatest contributor to increased urinary cotinine levels in both men and women. Among individuals who were exposed at work only, the reported degree of exposure agreed well with the mean urinary cotinine values. Those findings emphasize that the validation of exposure status with a biomarker is an essential prerequisite for epidemiological studies investigating passive smoking.
Unilateral ureteral obstruction (UUO) in rats has been used as a model of renal interstitial fibrosis, in which therapeutic trials can be of important clinical relevance. In this study, we ...investigated the effects of mycophenolate mofetil (MMF), the angiotensin-converting enzyme (ACE) inhibitor lisinopril (L), and the combination of both drugs, given daily for 14 days to UUO rats, on the renal fibrogenic process triggered by UUO.
Rats underwent surgical UUO, followed by treatment with daily doses of either MMF, lisinopril, or both, and were then sacrificed after 14 days. Kidney fragments were fixed for histopathological examination (hematoxylin-eosin and periodic acid-Schiff reactive) and immunohistochemistry for myofibroblasts (alpha-smooth muscle actin; alpha-SMA) and macrophages (ED-1). Histomorphometrical analysis of collagen was performed with Sirius red staining, and collagen content was assessed by the amount of hydroxyproline. Cortex and medulla were analyzed separately.
MMF, lisinopril and MMF+L reduced the density of alpha-SMA- and ED-1-positive cells (p < 0.05), interstitial volume (p < 0.05) and decreased Sirius-red-stained areas by 54.6, 35.6 and 58.0%, and hydroxyproline content by 60.1, 49.7 and 62.7%, respectively. No differences were observed among treated groups.
MMF and the ACE inhibitor lisinopril attenuated the progression of the fibrogenic process of UUO in an equivalent manner. The combination of both drugs did not add any further improvement in the collagen content.
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