scholarly journals Far-field coseismic gravity changes related to the 2015 MW7.8 Nepal (Gorkha) earthquake observed by superconducting gravimeters in mainland China

2021 ◽  
Vol 5 (2) ◽  
pp. 141-148
Author(s):  
LeLin Xing ◽  
◽  
ZiWei Liu ◽  
JianGang Jia ◽  
ShuQing Wu ◽  
...  
Keyword(s):  
Mainland China ◽  
Far Field ◽  
Gorkha Earthquake ◽  
Gravity Changes ◽  
Superconducting Gravimeters

scholarly journals Various far-field hydrological responses during 2015 Gorkha earthquake at two distant wells

2020 ◽  
Author(s):  
Xudong Huang ◽  
Yu Zhang
Keyword(s):  
Water Level ◽  
Seismic Waves ◽  
Amplitude Ratio ◽  
Unconfined Aquifer ◽  
Water Levels ◽  
Earth Tides ◽  
Tibet Plateau ◽  
Far Field ◽  
Gorkha Earthquake ◽  
2015 Gorkha Earthquake

Abstract Aquifer hydraulic parameter can change during earthquakes. Continuous monitoring of the response of water level to seismic waves or solid Earth tides provides an opportunity to document how earthquakes influence hydrological properties. Here we use data of two groundwater wells, Dian-22 (D22) and Lijiang (LJ) well, in southeast Tibet Plateau in response to the 2015 Mw 7.8 Gorkha earthquake to illustrate hydrological implications. The coherences of water level and seismic wave before and after the far-field earthquake show systematic variations, which may confirm the coseismic dynamic shaking influence at high frequencies (f > 8 cpd). The tidal response of water levels in these wells shows abrupt coseismic changes of both phase shift and amplitude ratio after the earthquake, which may be interpreted as an occurrence in the vertical permeability of a switched semiconfined aquifer in the D22 well, or an enhancement unconfined aquifer in the LJ well . Using the continuous transmissivity monitoring, we show that the possible coseismic response for about 10 days and instant healing after 10 days to the earthquake. Thus, the dynamic shaking during the Gorkha earthquake may have caused the short term aquifer responses by reopening of preexisting vertical fractures and later healing at epicentral distances about 1500 km.

scholarly journals Various Far-Field Hydrological Responses During 2015 Gorkha Earthquake at Two Distant Wells

2020 ◽  
Author(s):  
Xudong Huang ◽  
Yu Zhang
Keyword(s):  
Water Level ◽  
Seismic Waves ◽  
Amplitude Ratio ◽  
Epicentral Distance ◽  
Water Levels ◽  
Earth Tides ◽  
Tibet Plateau ◽  
Far Field ◽  
Gorkha Earthquake ◽  
2015 Gorkha Earthquake

Abstract Aquifer hydraulic parameter can change during earthquakes. Continuous monitoring of the response of water level to seismic waves or solid Earth tides provides an opportunity to document how earthquakes influence hydrological properties. Here we use data of two groundwater wells, Dian-22 (D22) and Lijiang (LJ) well, in southeast Tibet Plateau in response to the 2015 Mw 7.8 Gorkha earthquake to illustrate hydrological implications. The coherences of water level and seismic wave before and after the far-field earthquake show systematic variations, which may confirm the coseismic dynamic shaking influence at high frequencies (f > 8 cpd). The tidal response of water levels in these wells shows abrupt coseismic increases of both phase shift and amplitude ratio after the earthquake, which may be interpreted as an increase in the horizontal permeability of a confined aquifer in D22 well, and an occurrence in the vertical permeability of a switched semiconfined aquifer with larger epicentral distance and but high seismic ground motion. Using the continuous transmissivity monitoring, we show that the possible preseismic initial for ~ 1 day, coseismic response for ~ 3 days and postseismic healing for ~ 10 days during the earthquake. Thus, the dynamic shaking during the Gorkha earthquake may have caused confined aquifers to semiconfined aquifers by reopening of preexisting vertical fractures and later healing at epicentral distances about 1500 km.

Hydrologic changes of in-situ gravimetry

Geophysics ◽  
2021 ◽  
pp. 1-46
Author(s):  
Min Zhang ◽  
Ziwei Liu ◽  
Qiong Wu ◽  
Yuntian Teng ◽  
Xiaotong Zhang ◽  
...  
Keyword(s):  
Water Level ◽  
Water Levels ◽  
Background Information ◽  
Specific Yield ◽  
Specific Storage ◽  
Aquifer Storage ◽  
Gravity Changes ◽  
Superconducting Gravimeters ◽  
Local Hydrology

Inter-seasonal and geodynamics-related gravity changes are important geoscientific signals that are extractable from gravimeter observations after deducing background information as local hydrology gravity effect. With two superconducting gravimeters (SGs, OSG-053 and iGrav-007) located in different tectonic units, continuous Global Navigation Satellite System data, and AG observations, Wuhan (China) is an ideal location for investigating the effects of gravity resulting from significant local hydrology mass variations. We processed ∼26 months of gravity data collected from the SGs in Wuhan and obtain residuals of -40 nm.s2 for OSG-053 and 100 for iGrav-007. The hydrological observations show an estimated gravity increase of 42 nm.s2 near iGrav-007, which mainly resulted from the increased unconfined water level with an aquifer-specific yield of approximately 0.1. However, the gravity changes around OSG-053 are mainly from soil moisture and reach -90 nm.s2. The soil type, thickness and water content parameters were obtained from hydrogeological survey and drilling data. The deep confined water level rose by 2.5 m, which introduced a 1 nm.s2 gravity variation with a specific storage about 0.00001 from field unsteady flow pumping test. The modeled gravity is approximately -40 nm.s2 around OSG-053 and 90 around iGrav-007, in accordance with the observed gravity variations. The difference in gravity changes between the two SG observations can be explained by different local water storage environments. Our results suggest that unconfined and soil water significantly impact the in-situ gravimetry, which indicates that further detailed hydrogeological surveys are required. A combined investigation of gravity and water levels can be a useful approach to monitor aquifer storage conditions and groundwater management.

The benefits of performing continuous gravity measurements at active volcanoes using superconducting gravimeters

2020 ◽  
Author(s):  
Filippo Greco ◽  
Daniele Carbone ◽  
Flavio Cannavò ◽  
Alfio Messina ◽  
Danilo Contrafatto ◽  
...  
Keyword(s):  
Time Scales ◽  
Active Volcano ◽  
Continuous Measurements ◽  
Gravity Changes ◽  
Superconducting Gravimeters ◽  
Close Proximity ◽  
Gravity Measurements ◽  
Long Time ◽  
Changes Over Time ◽  
Active Volcanoes

<p>Continuous gravity measurements at active volcanoes are mostly accomplished using spring gravimeters, that can be operated under harsh field conditions. Unfortunately, these instruments do not provide reliable continuous measurements over long time-scales, due to the instrumental drift and artifacts driven by ambient parameters.</p><p>An alternative to spring devices for continuous measurements is given by superconducting gravimeters (SGs), that are free from instrumental effects and thus allow to track even small gravity changes over time-scales from minutes to years. Nevertheless, SGs cannot be deployed in close proximity to the active structures of tall volcanoes, since they need host facilities with main electricity and a large installation surface.</p><p>The mini-array of three SGs that were installed on Etna between 2014 and 2016 makes the first network of SGs ever installed on an active volcano. Here we present results from these instruments and show that, even though they are installed at relatively unfavorable positions (in terms of distances from the summit active craters), SGs can detect volcano-related gravity changes that would otherwise remain hidden, thus providing unique insight into the bulk processes driving volcanic activity.</p>

scholarly journals Various far-field hydrological responses during 2015 Gorkha earthquake at two distant wells

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Xudong Huang ◽  
Yu Zhang
Keyword(s):  
Water Level ◽  
Seismic Waves ◽  
Amplitude Ratio ◽  
Water Levels ◽  
Earth Tides ◽  
Tibet Plateau ◽  
Far Field ◽  
Short Term ◽  
Gorkha Earthquake ◽  
2015 Gorkha Earthquake

AbstractAquifer hydraulic parameter can change during earthquakes. Continuous monitoring of the response of water level to seismic waves or solid Earth tides provides an opportunity to document how earthquakes influence hydrological properties. Here, we use data of two groundwater wells, Dian-22 (D22) and Lijiang (LJ) well, in southeast Tibet Plateau in response to the 2015 Mw 7.8 Gorkha earthquake to illustrate hydrological implications. The coherences of water level and seismic wave before and after the far-field earthquake show systematic variations, which may confirm the coseismic dynamic shaking influence at high frequencies (f > 8 cpd). The tidal response of water levels in these wells shows abrupt coseismic changes of both phase shift and amplitude ratio after the earthquake, which may be interpreted as an occurrence in the vertical permeability of a switched semiconfined aquifer in the D22 well, or an enhancement unconfined aquifer in the LJ well. Using the continuous short-term transmissivity monitoring, we show that the possible coseismic response for about 10 days and instant healing after 10 days to the causal earthquake impact. Thus, the dynamic shaking during the Gorkha earthquake may have caused the short-term aquifer responses by reopening of preexisting vertical fractures and later healing at epicentral distances about 1500 km.

Possible applications of fraunhofer holography in high resolution electron microscopy

1978 ◽  
Vol 36 (1) ◽  
pp. 222-223 ◽  
Author(s):  
N. Bonnet ◽  
M. Troyon ◽  
P. Gallion
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Transfer Function ◽  
Radiation Damage ◽  
High Resolution Electron Microscopy ◽  
Far Field ◽  
Field Region ◽  
Crystalline Materials ◽  
Resolution Electron ◽  
The Ideal

Two main problems in high resolution electron microscopy are first, the existence of gaps in the transfer function, and then the difficulty to find complex amplitude of the diffracted wawe from registered intensity. The solution of this second problem is in most cases only intended by the realization of several micrographs in different conditions (defocusing distance, illuminating angle, complementary objective apertures…) which can lead to severe problems of contamination or radiation damage for certain specimens.Fraunhofer holography can in principle solve both problems stated above (1,2). The microscope objective is strongly defocused (far-field region) so that the two diffracted beams do not interfere. The ideal transfer function after reconstruction is then unity and the twin image do not overlap on the reconstructed one.We show some applications of the method and results of preliminary tests.Possible application to the study of cavitiesSmall voids (or gas-filled bubbles) created by irradiation in crystalline materials can be observed near the Scherzer focus, but it is then difficult to extract other informations than the approximated size.

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