Effect of complex topography on the wavefield recorded by DAS and buried fiber optic cable at Azuma volcano, Northeast Japan

2020 ◽  
Author(s):  
Kentaro Emoto ◽  
Takeshi Nishimura ◽  
Hisashi Nakahara ◽  
Satoshi Miura ◽  
Mare Yamamoto ◽  
...  
Keyword(s):  
Seismic Waves ◽  
Fiber Optic ◽  
Velocity Structure ◽  
Incident Angle ◽  
Gaussian Function ◽  
Separation Distance ◽  
P Wave ◽  
Small Scale ◽  
Fiber Optic Cable ◽  
Access Road

<p>First DAS observation at Mt. Azuma, Japan was conducted in July 2019 using buried fiber optic cable along the road access to the volcano. Mt. Azuma is an active volcano located in the Tohoku region. Different from non-volcanic regions, wavefields in the volcano is more complex due to its topography and the strong heterogeneities beneath the volcanic edifice. The strength of the scattering of seismic waves due to small-scale velocity heterogeneities in the volcano is reported to be more than one order higher than that in the non-volcanic region. To estimate small-scale heterogeneities, a dense observation network is necessary. The high spatial resolution is one of the advantages of the DAS observation. Therefore, DAS observation in the volcano might be a good chance for the estimation of the small-scale heterogeneity.</p><p> </p><p>We used 14km length of the fiber optic cable buried along to the access road to the observatory near the summit installed by the Ministry of Land, Infrastructure, Transport and Tourism to monitor the volcanic activities. The spatial and temporal samplings were 10m and 1000Hz, respectively. The observation period was for 3 weeks. In addition to regional and teleseismic earthquakes, volcanic earthquakes were also observed. A teleseismic P-wave was analyzed to investigate the effect of small-scale heterogeneities. Because the incident angle of the teleseismic P-wave is almost vertical to the portion of the fiber optic cable used for the DAS observation, a simple model can be used. We calculate the cross-correlation coefficient (CCC) of waveforms between channels and analyze its dependence on the distances between channel pairs. The recorded wavefield was fluctuated by scattering due to the small-scale heterogeneities and different waveforms were recorded even though the propagation distances are the same. Therefore, the spatial variation of the waveforms of teleseismic P-wave recorded at surface stations would be related to the small-scale heterogeneities beneath of the array.</p><p> </p><p>The CCC decreases with increasing separation distance and converges to a constant value. This shape can be modeled by the Gaussian function and we defined the spatial scale of CCC by fitting the Gaussian function. The scale decreases with increasing frequency. The finite difference simulation of the wave propagation was performed by changing the velocity structure and compare the synthetic and observed CCCs. We found that the effect of the topography is most significant on the CCC. Because analyzed waveforms mainly consist of the converted surface wave from the teleseismic P-wave, the effect of subsurface small-scale heterogeneities is not significant. Our result shows that it is necessary to consider the effect of the topography in analyses of DAS data recorded in volcanoes.</p>

Surface topography effects on seismic ground motion and correlation with earthquake-induced landslide: An example of the JiuJiu peaks in 1999 Chi-Chi Taiwan earthquake

2020 ◽  
Author(s):  
Chun-Te Chen ◽  
Shiann-Jong Lee ◽  
Yu-Chang Chan
Keyword(s):  
Surface Topography ◽  
Seismic Response ◽  
Ground Motion ◽  
Seismic Waves ◽  
Velocity Structure ◽  
Seismic Hazard Assessment ◽  
Buffer Layers ◽  
Small Scale ◽  
Ground Shaking ◽  
Mesh Model

<p>The topography effect has been thriving investigated based on numerical modeling. It impacts the seismic ground shaking, usually amplifying the amplitude of shaking at top hills or ridges and de-amplifying at valleys. However, the correlation between the earthquake-induced landslide and the topographic amplification is relatively unexplored. To investigate the amplification of seismic response on the surface topography and the role in the Chi-Chi earthquake-induced landslide in the JiuJiu peaks area, we perform a 3D ground motion simulation in the JiuJiu peaks area of Taiwan based on the spectral element method. The Lidar-derived 20m resolution Digital Elevation Model (DEM) data was applied to build a mesh model with realistic terrain relief. To this end, in a steep topography area like the JiuJiu peaks, the designed thin buffer layers are applied to dampen the mesh distortion. The three doubling mesh layers near the surface accommodate a more excellent mesh model. Our results show the higher amplification of PGA on the tops and ridges of JiuJiu peaks than surrounding mountains, while the de-amplification mostly occurs near the valley and hillside. The relief topography could have a ±50% variation in PGA amplification for compression wave, and have much more variety in PGA amplification for shear wave, which could be in the range between -50% and +100%. We also demonstrate that the high percentages of the landslide distribution right after the large earthquake are located in the topographic amplified zone. The source frequency content interacts with the topographic feature, in general, small-scale topography amplifies the higher-frequency seismic waves. It is worthy of further investigating the interaction between the realistic topography and the velocity structure on how to impact the seismic response in the different frequency bands. We suggest that the topographic seismic amplification should be taking into account in seismic hazard assessment and landslide evaluation.</p>

Repeat well logging using earthquake wave amplitudes measured by distributed acoustic sensors

2020 ◽  
Vol 39 (7) ◽  
pp. 513-517
Author(s):  
Roman Pevzner ◽  
Boris Gurevich ◽  
Anastasia Pirogova ◽  
Konstantin Tertyshnikov ◽  
Stanislav Glubokovskikh
Keyword(s):  
Seismic Waves ◽  
Fiber Optic ◽  
Synthetic Data ◽  
Seismic Source ◽  
Small Scale ◽  
Acoustic Sensors ◽  
Linear Strain ◽  
Subsurface Characterization ◽  
Distributed Acoustic Sensing ◽  
Subsurface Monitoring

Well-based technologies for seismic subsurface monitoring increasingly utilize fiber-optic cables installed in boreholes as distributed acoustic sensing (DAS) systems. A DAS cable allows measuring linear strain of the fiber and can serve as an array of densely spaced seismic receivers. The strain amplitudes recorded by the DAS cable depend on the near-well formation properties (the softer the medium, the larger the strain). Thus, these properties can be estimated by measuring relative variations of the amplitudes of seismic waves propagating along the well. An advantage of such an approach to subsurface characterization and monitoring is that no active seismic source is required. Passive sources such as earthquakes can be utilized. A synthetic data example demonstrates viability of the approach for monitoring of small-scale CO2 injection into an aquifer. Two field DAS data examples based on signal recordings from several distant earthquakes show that the relevant properties of the near-well formation can be estimated with an accuracy of approximately 5%.

scholarly journals Very broadband strain-rate measurements along a submarine fiber-optic cable off Cape Muroto, Nankai subduction zone, Japan

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Satoshi Ide ◽  
Eiichiro Araki ◽  
Hiroyuki Matsumoto
Keyword(s):  
Subduction Zone ◽  
Fiber Optic ◽  
Ocean Current ◽  
Small Scale ◽  
Distributed Temperature Sensing ◽  
Fiber Optic Cable ◽  
Deep Ocean Water ◽  
Wide Range ◽  
Rapid Temperature ◽  
Nankai Subduction Zone

AbstractDistributed acoustic sensing (DAS) is a new method that measures the strain change along a fiber-optic cable and has emerged as a promising geophysical application across a wide range of research and monitoring. Here we present the results of DAS observations from a submarine cable offshore Cape Muroto, Nankai subduction zone, western Japan. The observed signal amplitude varies widely among the DAS channels, even over short distances of only ~ 100 m, which is likely attributed to the differences in cable-seafloor coupling due to complex bathymetry along the cable route. Nevertheless, the noise levels at the well-coupled channels of DAS are almost comparable to those observed at nearby permanent ocean-bottom seismometers, suggesting that the cable has the ability to detect nearby micro earthquakes and even tectonic tremors. Many earthquakes were observed during the 5-day observation period, with the minimum and maximum detectable events being a local M1.1 event 30–50 km from the cable and a teleseismic Mw7.7 event that occurred in Cuba, respectively. Temperature appears to exert a greater control on the DAS signal than real strain in the quasi-static, sub-seismic range, where we can regard our DAS record as distributed temperature sensing (DTS) record, and detected many rapid temperature change events migrating along the cable: a small number of large migration events (up to 10 km in 6 h) associated with rapid temperature decreases, and many small-scale events (both rising and falling temperatures). These events may reflect oceanic internal surface waves and deep-ocean water mixing processes that are the result of ocean current–tidal interactions along an irregular seafloor boundary.

scholarly journals Very broadband strain-rate measurements along a submarine fiber-optic cable off Cape Muroto, Nankai subduction zone, Japan

2021 ◽  
Author(s):  
Satoshi Ide ◽  
Eiichiro Araki ◽  
Hiroyuki Matsumoto
Keyword(s):  
Subduction Zone ◽  
Fiber Optic ◽  
Ocean Current ◽  
Small Scale ◽  
Distributed Temperature Sensing ◽  
Fiber Optic Cable ◽  
Deep Ocean Water ◽  
Wide Range ◽  
Rapid Temperature ◽  
Nankai Subduction Zone

Abstract Distributed acoustic sensing (DAS) is a new method that measures the strain change along a fiber-optic cable and has emerged as a promising geophysical application across a wide range of research and monitoring. Here we present the results of DAS observations from a submarine cable offshore Cape Muroto, Nankai subduction zone, western Japan. The observed signal amplitude varies widely among the DAS channels, even over short distances of only ~100 m, which is likely attributed to the differences in cable-seafloor coupling due to complex bathymetry along the cable route. Nevertheless, the noise levels at the well-coupled channels of DAS are almost comparable to those observed at nearby permanent ocean-bottom seismometers, suggesting that the cable has the ability to detect nearby micro earthquakes and even tectonic tremors. Many earthquakes were observed during the five-day observation period, with the minimum and maximum detectable events being a local M1.1 event 30–50 km from the cable and a teleseismic Mw7.7 event that occurred in Cuba, respectively. Temperature appears to exert a greater control on the DAS signal than real strain in the quasi-static, sub-seismic range, where we can regard our DAS record as distributed temperature sensing (DTS) record, and detected many rapid temperature change events migrating along the cable: a small number of large migration events (up to 10 km in 6 hours) associated with rapid temperature decreases, and many small-scale events (both rising and falling temperatures). These events may reflect oceanic internal surface waves and deep-ocean water mixing processes that are the result of ocean current–tidal interactions along an irregular seafloor boundary.

scholarly journals Very Broadband Strain-Rate Measurements Along a Submarine Fiber-Optic Cable Off Cape Muroto, Nankai Subduction Zone, Japan

2020 ◽  
Author(s):  
Satoshi Ide ◽  
Eiichiro Araki ◽  
Hiroyuki Matsumoto
Keyword(s):  
Subduction Zone ◽  
Fiber Optic ◽  
Ocean Current ◽  
Small Scale ◽  
Ocean Bottom ◽  
Fiber Optic Cable ◽  
Deep Ocean Water ◽  
Wide Range ◽  
Rapid Temperature ◽  
Nankai Subduction Zone

Abstract Distributed acoustic sensing (DAS) is a new method that measures the strain change along a fiber-optic cable and has emerged as a promising geophysical application across a wide range of research and monitoring. Here we present the results of DAS observations from an submarine cable offshore Cape Muroto, Nankai subduction zone, western Japan. The observed signal amplitude varies widely among the DAS channels, even over short distances of only ~100 m, which is likely attributed to the differences in cable-seafloor coupling due to complex bathymetry along the cable route. Nevertheless, the noise levels at the well-coupled channels of DAS are almost comparable to those observed at nearby permanent ocean-bottom seismometers. Many earthquakes were observed during the five-day observation period, with the minimum and maximum detectable events being a local M1.1 event 30–50 km from the cable and a teleseismic Mw7.7 event that occurred in Cuba, respectively. Temperature appears to exert a greater control on the DAS signal than real strain in the quasi-static, sub-seismic range. We observed many rapid temperature change events migrating along the cable: a small number of large migration events (up to 10 km in 6 hours) associated with rapid temperature increases, and many small-scale events (both rising and falling temperatures). These events may reflect deep-ocean water mixing processes that are the result of ocean current–tidal interactions along an irregular seafloor boundary.

scholarly journals 3D Seismic Waves Velocity Structure of West Sumatera Seismic Waves Using Earthquake Data from January 2010-December 2017

2021 ◽  
Vol 873 (1) ◽  
pp. 012003
Author(s):  
Rizki Wulandari ◽  
Tedi Yudistira ◽  
Erlangga Ibrahim Fattah ◽  
Atin Nur Aulia ◽  
Adhi Wibowo
Keyword(s):  
Fault Zone ◽  
Seismic Tomography ◽  
Seismic Waves ◽  
Velocity Structure ◽  
Secondary Data ◽  
Velocity Model ◽  
P Wave ◽  
3D Seismic ◽  
Time Data ◽  
West Sumatra

Abstract This study analyses the P wave velocity (Vp) and Vp/Vs based on 3D seismic tomography in West Sumatra. Seismic tomography is a method of reconstructing the image of the subsurface structure of the earth using travel time data. This research uses secondary data obtained from the Incorporated Research Institutions for Seismology (IRIS) from January 2010 to December 2017. The data obtained were 472 earthquake events and 21 seismic stations that recorded the earthquake events. This research consists of are the hypocenter relocation, which will simultaneously renew the 1D velocity model using VELEST software, and tomographic inversion using SIMULPS12 software. The minimum anomaly of Vp/Vs value is around 1.39, while the maximum anomaly Vp/Vs value is around 2.05. The Vp distribution results have low and high Vp/Vs values around Sumatra Fault Zone and Mentawai Fault Zone. Anomaly results from the tomogram of these areas have an association with saturated pressure sedimentary areas and the presence of fractures which will further contribute to earthquake events.

Turning a Telecom Fiber-Optic Cable into an Ultradense Seismic Array for Rapid Postearthquake Response in an Urban Area

2021 ◽  
Author(s):  
Xiangfang Zeng ◽  
Feng Bao ◽  
Clifford H. Thurber ◽  
Rongbing Lin ◽  
Shuofan Wang ◽  
...  
Keyword(s):  
Ground Motion ◽  
Early Warning ◽  
Fiber Optic ◽  
Small Scale ◽  
Monitoring Networks ◽  
Motion Pattern ◽  
Fiber Optic Cable ◽  
Epicentral Area ◽  
Distributed Acoustic Sensing ◽  
Deployment Time

Abstract Aftershock-monitoring networks deployed in the epicentral area of a damaging earthquake play important roles in earthquake early warning and ShakeMap estimation, which contribute to hazard mitigation. Using distributed acoustic sensing (DAS) technology with dark fiber can significantly reduce deployment time and cost, and improve spatial sampling, both of which help capture more aftershocks. In this study, we used a 7.6 km dark fiber in Tangshan, China, to monitor seismicity after the 12 July 2020 Ms 5.1 earthquake. The DAS array detected dozens of earthquakes missed by the local permanent network that doubled the number of aftershocks. The relocated aftershocks are distributed mainly north of the DAS array, and the ground-motion pattern changes also hint small-scale features. Our successful results demonstrate the feasibility of using DAS and dark fiber for rapid postearthquake response.

scholarly journals Interaction between interplate fault topography and tsunamigenic structures at the subduction zone offshore West Mexico

2020 ◽  
Author(s):  
Rafael Bartolome ◽  
Manel Prada ◽  
Claudia Gras ◽  
Slaven Begovic ◽  
William Bandy ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Structural Integrity ◽  
Velocity Structure ◽  
P Wave ◽  
Small Scale ◽  
Mexican Pacific ◽  
Obs Data ◽  
Vp Structure ◽  
Rivera Plate ◽  
Refracted Waves

<p>The megathrust topography is key in conditioning the structural integrity of the overriding plate, and thus, the generation of tsunamigenic structures. Our objective is to investigate the Rivera subduction zone, offshore the Mexican Pacific coast, known for hosting large megathrust tsunamigenic earthquakes (Mw > 7.5), and where little is known regarding the distribution of tsunamigenic structures along the margin. Our working hypothesis is that there is an interaction between the megathrust relief at the surface of the subducted slab (Rivera Plate) and the existence of tsunamigenic structures in the above unsubducted plate (North America). To investigate this interaction, we used seismic methods to characterize the variations of the physical properties of the overriding plate, generally related to tectonic (faults) structures that are sources of tsunamis, with the reliefs of the deeper subducted plate obtained with the same method. Here, we use spatially coincident 2D multichannel seismic (MCS, 5.85 km long-streamer) and active marine wide-angle seismic (WAS) data acquired during the TSUJAL survey in 2014 offshore west of Mexico to measure structural variations of the overriding plate and the megathrust interface. We have jointly inverted refracted and reflected travel-times (TT) from both MCS and WAS data to constrain the P-wave velocity (Vp) structure of the overriding plate and the geometry of the megathrust. Before the inversion and to increase the amount of refracted TT we have applied the downward continuation technique to MCS field data allowing to better image the refracted waves in the records. MCS data has a higher spatial sampling than OBS data, which translates into a higher density sampling of the refracted waves and hence the tomographic resolution. Therefore, the resulting tomographic model displays small-scale velocity structure variations of the overriding plate and the megathrust relief that would not be resolved with TT from OBS data only. We used further refracted and reflected TT from OBS data to constrain the Vp structure of the subducting oceanic plate and the geometry of the oceanic Moho. The inverted megathrust interface obtained with the tomography shows clear topographic features in its shallow portion (<~10 km from the trench). Such topographic variations are smaller than the average size of seamounts of the Rivera plate, but they are similar to the seafloor fabric generated by a relict East Pacific Rise segment identified west of the trench in the bathymetry map of the region. Time-migrated images were also obtained after processing the MCS data to constrain the tectonic framework of the shallow subduction zone regardless of the tomographic models. The seismic sections reveal the lack of an extensive accretionary prism, implying that subduction-erosion dominates the structure of the margin in this region. Integrating all the data results, we find that megathrust highs correlate with low-velocity anomalies, suggesting the presence of fluids, and correlate with the presence of extensional faults in the overriding plate as well. This correlation demonstrates the control that megathrust topography exerts on the formation of tsunamigenic structures along the Rivera plate boundary.</p>

scholarly journals 1-D velocity structure modelling of the Earth's Crust in the NW Dinarides

2021 ◽  
Author(s):  
Gregor Rajh ◽  
Josip Stipčević ◽  
Mladen Živčić ◽  
Marijan Herak ◽  
Andrej Gosar ◽  
...  
Keyword(s):  
Crustal Structure ◽  
Velocity Structure ◽  
Pannonian Basin ◽  
Stable Solution ◽  
P Wave ◽  
Small Scale ◽  
Depth Range ◽  
Eurasian Plate ◽  
Low Velocity ◽  
Velocity Models

Abstract. The investigated area of the NW Dinarides is located at the NE corner of the Adriatic microplate and is bordered by the Adriatic foreland, the Southern Alps, and the Pannonian basin. Its complex crustal structure is the result of interactions among different tectonic units, mainly the Eurasian plate and the Adriatic microplate. Despite numerous seismic studies in this tectonically complex area, there is still a need for a detailed, small scale study focusing mainly on the upper, brittle part of the crust. We investigated the crustal velocity structure with 1-D simultaneous hypocenter-velocity inversion using routinely picked P wave arrival times. Most of the computed models converged to a stable solution in the depth range between 0 and 26 km. We further evaluated the inversion results with hypocenter shift tests, high and low velocity tests, and relocations. This helped us to select two best performing velocity models for the whole study area. Based on these results and the seismicity distribution, we further divided the study area into three parts, redefined the earthquake-station geometry, and performed inversion for each part separately to gain better insight into the crustal structure of each subregion. Median velocities in the upper 20 km of the crust in the eastern subregion are lower compared to the regional median and the median of the other two subregions. The northwestern and southwestern subregions are very similar in terms of crustal structure between about 8 and 23 km depth. The largest difference between them is observed in the upper 8 km, with higher median velocities in the southwestern subregion. Compared to the model currently used at Slovenian Environment Agency to locate earthquakes, the velocity models obtained show higher velocities in the upper 30 km depth and agree very well with some of the previous studies. In addition to general structural implications and a potential for improving seismic tomography results, the new 1-D velocity models can also be used for fast routine earthquake location and for detecting systematic travel time errors in seismological bulletins.

The ROLE OF CHINA-PAK ECONOMIC CORRIDOR (CPEC) IN LOGISTIC SYSTEM OF PAKISTAN’S AND CHINA’S

2019 ◽  
Vol 6 (1) ◽  
pp. 48-50
Author(s):  
Ikram Uddin
Keyword(s):  
Persian Gulf ◽  
Lead Time ◽  
Fiber Optic ◽  
Delivery Time ◽  
Fiber Optic Cable ◽  
Total Cost ◽  
Economic Complexity ◽  
Shipping Cost ◽  
The Impact

This study will explain the impact of China-Pak Economic Corridor (CPEC) on logistic system of China and Pakistan. This project is estimated investment of US $90 billion, CPEC project is consists of various sub-projects including energy, road, railway and fiber optic cable but major portion will be spent on energy. This project will start from Kashgar port of china to Gwadar port of Pakistan. Transportation is sub-function of logistic that consists of 44% total cost of logistic system and 20% total cost of production of manufacturing and mainly shipping cost and transit/delivery time are critical for logistic system. According to OEC (The Observing Economic Complexity) currently, china is importing crude oil which 13.4% from Persian Gulf. CPEC will china for lead time that will be reduced from 45 days to 10 days and distance from 2500km to 1300km. This new route will help to china for less transit/deliver time and shipping cost in terms of logistic of china. Pakistan’s transportation will also improve through road, railway and fiber optic cabal projects from Karachi-Peshawar it will have speed 160km per hour and with help of pipeline between Gwadar to Nawabshah gas will be transported from Iran. According to (www.cpec.inf.com) Pakistan logistic industry will grow by US $30.77 billion in the end of 2020.

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