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Rupture imaging of the 25 April 2015 M_W7.9 Nepal earthquake from back-projection of teleseismic P waves

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Earthquake Science 2018年第4期31卷 199-207页

作者： Yong Qiu Qiaoxia Liu Geophysical Exploration Center China Earthquake Administration

The M7.9 Nepal earthquake of 25 April2015 had over 8, 500 fatalities and was the most destructive earthquake in Nepal since the Bihar-Nepal earthquake in 1934.In this study, we imaged the rupture process of this Nepal event by back-projecting the teleseismic P-wave energy recorded at the three regional networks in Alaska, Australia and Europe. The back-projection images of the three subarrays revealed that the Nepal earthquake propagated along the strike in a southeast direction over a distance of ～ 160–170 km with the duration of ～ 50–55 s. The rupture process was found to be a simple, unilateral event with a near constant velocity of 3.3 km/s.The beam power was mainly distributed in the geographic region just north of Kathmandu and the peak intensity for the source time function curve occurred at about 30 s. The earthquake was destructive due to its occurrence at shallow depth(～ 12–15 km) and the fact that the capital lies in a basin of soft sediment. Additionally, the resonance effect for the longer period waves that occurred in the Kathmandu valley led to destructive aggravation, impacting mainly the taller buildings.

关键词： rupture imaging Nepal MW7.9 earthquake back-projection regional arrays

Image Reconstruction from Fan-Beam projections without back-projection Weight in a 2-D Dynamic CT: Compensation of Time-Dependent Rotational, Uniform Scaling and Translational Deformations

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Open Journal of Medical Imaging 2013年第4期3卷 136-143页

作者： A. V. Narasimhadhan Aman Sharma Dipen Mistry National Institute of Technology Goa Goa India National Institute of Technology Karnataka Surathkal India

In a dynamic CT, the acquired projections are corrupted due to strong dynamic nature of the object, for example: lungs, heart etc. In this paper, we present fan-beam reconstruction algorithm without position-dependent backprojection weight which compensates for the time-dependent translational, uniform scaling and rotational deformations occurring in the object of interest during the data acquisition process. We shall also compare the computational cost of the proposed reconstruction algorithm with the existing one which has position-dependent weight. To accomplish the objective listed above, we first formulate admissibility conditions on deformations that is required to exactly reconstruct the object from acquired sequential deformed projections and then derive the reconstruction algorithm to compensate the above listed deformations satisfying the admissibility conditions. For this, 2-D time-dependent deformation model is incorporated in the fan-beam FBP reconstruction algorithm with no backprojection weight, assuming the motion parameters being known. Finally the proposed reconstruction algorithm is evaluated with the motion corrupted projection data simulated on the computer.

关键词： Fan-Beam Reconstruction Algorithm Hilbert Filter Virtual Acquisition Geometry Equiangular Detector Geometry Rotational Uniform Scaling and Translational Deformation Position Dependent back-projection Weight

Estimating Seismic Intensity Maps of the 2021 Mw 7.3 Madoi,Qinghai and Mw 6.1 Yangbi,Yunnan,China Earthquakes

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Journal of Earth Science 2022年第4期33卷 839-846页

作者： Wenkai Chen Dun Wang Can Zhang Qiang Yao Hongjun Si Lanzhou Institute of Seismology China Earthquake AdministrationLanzhou 730000China State Key Laboratory of Geological Processes and Mineral Resources School of Earth SciencesChina University of GeosciencesWuhan 430074China Seismological Research Institute Inc. Tokyo 113-0032Japan

This study focuses on rapidly determining seismic intensity maps of earthquakes because it offers fundamental information for effective emergency rescue and subsequent scientific research,and remains challenging to accurately determine seismic intensity map in regions with sparse instrumental observations.Here we applied a novel method that consisted of array technology(backprojection),ground-motion prediction equations,and site corrections,to estimate the seismic intensity maps of the 2021 Mw 7.3 Madoi,Qinghai and the Mw 6.1 Yangbi,Yunnan,China earthquakes.We used seismic data recorded at European stations to back-project the source processes of the 2021 Mw7.3 Madoi,Qinghai and the Mw 6.1 Yangbi,Yunnan,China earthquakes.The back-projected energy radiations were then used as subevents or used to define the fault geometry.Summing the contributions of each subevent or estimating the shortest distances from each site to the rupture fault,we obtained the ground motion(PGA and PGV)for each site under rock site conditions.The estimated ground motions were corrected at each site for local site amplification according to the Vs30 database.Our estimated seismic intensity maps and field reports showed high similarity,which further validated the effectiveness of the novel approach,and pushed the limit of earthquake size down to~M 6.Such efforts would substantially help in the fast and accurate evaluation of earthquake damage,and precise rescue efforts.

关键词： earthquakes seismic intensity map back-projection ground-motion prediction equations

Rapid assessment of the September 5,2022 M_(S)6.8 Luding earthquake in Sichuan,China

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Earthquake Research Advances 2023年第2期3卷 1-7页

作者： Dengjie Kang Wenkai Chen Huaiqun Zhao Dun Wang Lanzhou Institute of Seismology Lanzhou730000GansuChina China University of Geosciences(Wuhan) Wuhan430000HubeiChina

At 12:52,September 5,2022,an M_(S)6.8 earthquake occurred in Luding,Sichuan.The earthquake caused serious casualties and property loss,and was determined to have an epicenter intensity of Ⅸ degree.In this study,we used three earthquake intensity rapid assessment methods(i.e.WFM,BPM and ASM) to evaluate the intensity of this earthquake.Then,we comparatively analyzed the three methods based on strong ground motion observation data and actual intensity maps.The results show that:(1) The earthquake is associated with a southeast-oriented single-sided rupture.The WFM method can only evaluate earthquakes with two-sided ruptures,which has some limitations;(2) The intensity of BPM and ASM was overestimated on the southwest and north sides of the epicenter,but other high-intensity zones were similar to the intensities measured by actual surveys;(3) The residuals of the three intensity assessment methods were all between-0.5 and 1.Although a small number of stations were underestimated,the overall residuals were good,and the residuals gradually approached 0 with the increase of distance;(4) The number of towns and villages evaluated by the three methods in the earthquake area was almost all lower than the field survey results.One exception is the area of Ⅷ degree,where the BPM and ASM were higher than the survey results;(5) The area of the earthquake area evaluated by the three methods was low in Ⅵ and Ⅶ degree,moderate in Ⅷ degree,and low in Ⅸ degree(the area from ASM is similar to the area measured by actual survey).Overall,ASM is applicable to this earthquake intensity assessment.

关键词： Luding earthquake Seismic intensity Rapid assessment Ground-Motion prediction equation back-projection Aftershock

Magnitude of the 23 January 2018 M7.9 Alaska Earthquake Estimated from Local Dense Seismic Records in Alaska

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Journal of Earth Science 2019年第5期30卷 1005-1009页

作者： Chen Song Qiang Yao Dun Wang Key Laboratory of Earthquake Geodesy Institute of Seismology China Earthquake Administration Wuhan 430071 China State Key Laboratory of Geological Processes and Mineral Resources School of Earth Sciences China University of Geosciences Wuhan 430074 China

We apply a novel method to estimate the magnitude of the 23 January 2018 M7.9 Alaska earthquake using seismic stations recorded at local to regional distances in Alaska, US. We determine the source duration from back-projection results derived from the Alaska stations in a relatively compact azimuth range. Then we calculate the maximum P-wave displacements recorded on a wide azimuth range at distances of 8 to 15 degrees. Combining the source duration and the maximum P-wave displacements, we obtain magnitudes of 7.86–8.03 for the 23 January 2018 earthquake in 3–5 min, very close to the Mw 7.9 determined by the USGS and GCMT. This example validates the new approach for determining magnitude of large earthquakes using local to regional stations, and its time efficiency that magnitudes of large earthquakes can be accurately estimated within in 3–5 min after origin time. Therefore, further application of this new method would help accurate estimation of size of earthquakes that occur offshore and might cause tsunami hazards.

关键词： rapid magnitude estimation back-projection real-time seismology tsunami warning geophysics

Imaging the rupture process of the 10 January 2018 Mw7.5 Swan island, Honduras earthquake

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Earthquake Science 2020年第4期33卷 194-200页

作者： Chuang Cheng Dun Wang School of Earth Sciences China University of GeosciencesWuhan 430074China

The 10 January 2018 Mw7.5 Swan island,Honduras earthquake occurred on the Swan island fault,which is a transform plate boundary between the North American and Caribbean plates.Here we back-project the rupture process of the earthquake using dense seismic stations in Alaska,and find that the earthquake ruptured at least three faults(three stages)for a duration of~40 s.The rupture speed for the longest fault(stage 3)is as fast as 5 km/s,which is much faster than the local shear wave velocity of~4 km/s.Supershear rupture was incidentally observed on long and straight strike-slip faults.This study shows a supershear rupture that occured on a strike-slip fault with moderate length,implying that supershear rupture might commonly occur on large strike-slip earthquakes.The common occurrence of supershear rupture on strike-slip earthquakes will challenge present understanding of crack physics,as well as strong ground motion evaluation in earthquake engineering.

关键词： 2018 Mw7.5 Honduras earthquake source process back-projection rupture speed supershear rupture

Source complexity of the 2016 M_W7.8 Kaikoura (New Zealand) earthquake revealed from teleseismic and InSAR data

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Earth and Planetary Physics 2018年第4期2卷 310-326页

作者： HaiLin Du Xu Zhang LiSheng Xu WanPeng Feng Lei Yi Peng Li Institute of Geophysics China Earthquake Administration Canada Center for Mapping and Earth Observation Natural Resources Canada School of Geodesy and Geomatics Wuhan University College of Marine Geosciences Ocean University of China

On November 13, 2016, an MW7.8 earthquake struck Kaikoura in South Island of New Zealand. By means of back-projection of array recordings, ASTFs-analysis of global seismic recordings, and joint inversion of global seismic data and co-seismic In SAR data, we investigated complexity of the earthquake source. The result shows that the 2016 MW7.8 Kaikoura earthquake ruptured about 100 s unilaterally from south to northeast(~N28°–33°E), producing a rupture area about 160 km long and about 50 km wide and releasing scalar moment 1.01×1021 Nm. In particular, the rupture area consisted of two slip asperities, with one close to the initial rupture point having a maximal slip value ~6.9 m while the other far away in the northeast having a maximal slip value ~9.3 m. The first asperity slipped for about 65 s and the second one started 40 s after the first one had initiated. The two slipped simultaneously for about 25 s.Furthermore, the first had a nearly thrust slip while the second had both thrust and strike slip. It is interesting that the rupture velocity was not constant, and the whole process may be divided into 5 stages in which the velocities were estimated to be 1.4 km/s, 0 km/s, 2.1 km/s, 0 km/s and 1.1 km/s, respectively. The high-frequency sources distributed nearly along the lower edge of the rupture area, the highfrequency radiating mainly occurred at launching of the asperities, and it seemed that no high-frequency energy was radiated when the rupturing was going to stop.

关键词： 2016 MW7.8 Kaikoura earthquake back-projection of array recordings ASTFs-analysis of global recordings joint inversion of teleseismic and InSAR data complexity of source

Novel Channel Attention Residual Network for Single Image Super-Resolution

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Journal of Beijing Institute of Technology 2020年第3期29卷 345-353页

作者： Wenling Shi Huiqian Du Wenbo Mei School of Information and Electronics Beijing Institute of TechnologyBeijing 100081China

A novel channel attention residual network(CAN)for SISR has been proposed to rescale pixel-wise features by explicitly modeling interdependencies between channels and encoding where the visual attention is located.The backbone of CAN is channel attention block(CAB).The proposed CAB combines cosine similarity block(CSB)and back-projection gating block(BG).CSB fully considers global spatial information of each channel and computes the cosine similarity between each channel to obtain finer channel statistics than the first-order statistics.For further exploration of channel attention,we introduce effective back-projection to the gating mechanism and propose BG.Meanwhile,we adopt local and global residual connections in SISR which directly convey most low-frequency information to the final SR outputs and valuable high-frequency components are allocated more computational resources through channel attention mechanism.Extensive experiments show the superiority of the proposed CAN over the state-of-the-art methods on benchmark datasets in both accuracy and visual quality.

关键词： back-projection cosine similarity residual network super-resolution

Rupture pattern of the Oct 23,2011 Van-Merkez,Eastern Turkey earthquake

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Earthquake Science 2014年第3期27卷 257-264页

作者： Hao Zhang Zengxi Ge Department of Geophysics School of Earth and Space SciencesPeking University Department of Earth and Planetary Sciences Northwestern University2145 Sheridan RdEvanstonIL 60208USA

High-frequency rupture process of the Oct 23, 2011 Van-Merkez earthquake is imaged by back-projection method using high-quality teleseismic P wave data from the US Array, and prestack Kirchhoff migration using P wave data from a subarray of global seismic networks. The rupture model with two asperities is confirmed by previous two methods. In low-frequency imaging, a large asperity derived from the migration method corresponds to the second one from the high-frequency P waves. The con- sistency of the locations of asperities from datasets with different frequency bands indicates that there is possible insignificance of the frequency-dependent feature for the earthquake. The resultant images illustrate the spatial and temporal evolution of the rupture, which mainly propa- gated WSW over a length of 33 km during the first 18 s, accompanying with bursts of two asperities at 3 and 11-13 s. The rupture direction is confirmed by the S wave comer frequency variations of strong ground accelerations. The rupture fronts are mainly located at the updip of the causative fault. Based on polarities of the P waveforms and focal mechanisms of the mainshock and aftershocks, the failure of these two asperities is determined to have occurred on a reverse fault with a dip angle of 47°. Hence, the rupture pattern of the 2011 Van-Merkez earthquakewas dominated by a unilateral rupture toward the west- southwest direction.

关键词： 2011 Van-Merkez earthquake· Rupturepattern back-projection Kirchhoff migration