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Papers by xianjie zha

In the past two decades, dental implants have been an essential component of the public health. H... more In the past two decades, dental implants have been an essential component of the public health. However, lack of a reliable and safe dental surgery imaging modality remains a major problem. Optical coherence tomography (OCT) is an interferometic optical imaging modality that is somewhat similar to B-mode ultrasound but utilizes infrared light instead of sound waves. It can provide optical biopsy at a very high resolution and in real time. The compact fiber-optic components of OCT make it easy to integrate into dental drill bit to provide the dentists with real-time image feedback about the anatomical structure in the vicinity of the drill bit. This research focuses on the image processing for such a concept designing OCT integrated dental drilling system. Various image processing methods are applied to the OCT images with the intention of finding out the suitable solutions for speckle noise reduction, image reconstruction and dental tissues segmentation. OCT imaging system obtains the cross sectional structure of samples by measuring the back reflected light. The coherent detection makes the OCT images are always subject to speckle noise. The existence of speckle noise limits the interpretation of OCT images. In this study, various speckle reduction digital filters are applied to the images obtained from OCT during high speed rotation. Our results indicate that the adaptive Wiener filter is particularly suitable for our specific application. It is a time–saving method that not only significantly suppresses speckle noise but also preserves image edges. The study also concerns the image restoration due to the non-uniform rotational scanning. One modified method based on the cross correlation between successive A-scans is posted and studied. The assembled images indicate our algorithm is capable of reconstructing the manually-scanned images with an acceptable assemble accuracy. In tissue segmentation, the porous structure of the trabecular bones enables us to discriminate different them from cortical bones. However, due to the intensity decay along the depth direction, the way for image automatic segmentation is still a major problem need to be solved in future research. To test and verify our algorithms, the experiments are conducted to both real animal jawbones and silicone elastomer-based optical tissue phantoms. This proof-of-concept study shows that OCT is able to probe dental tissues in rotational scanning. The results from both samples are highly in accord with each other. This conclusion suggests that our optical phantom is a good jawbone substitute. The durable, easy-to-make phantoms can significantly reduce the cost of future researches.

Bulletin of the Seismological Society of America

The hidden Haicheng fault system is an earthquake-prone zone on the Liaodong Peninsula, China. It... more The hidden Haicheng fault system is an earthquake-prone zone on the Liaodong Peninsula, China. Its seismogenic structure is still unclear and needs further study. In this study, we used the differential evolution algorithm to invert the waveform data of the 2008 ML 4.8 Haicheng earthquake and the 2012 ML 4.8 Gaizhou earthquake and obtained an updated 1D crustal velocity model. The model reveals a low-velocity zone with a depth of 18–24 km below the Haicheng fault zone. Based on the velocity model, we used the arrival-time data to accurately locate the earthquakes that occurred in the Haicheng area from 2008 to 2018. The relocated earthquakes show that the Az 300°-trending Haicheng fault consists of two segments spaced about 2 km apart, namely the western and the eastern segments. They are about 12 and 22 km long and inclined to the northeast with dips of 70° and 80°, respectively. These seismogenic structures of the Haicheng fault zone are important for assessing the future seismic ...

International Journal of Remote Sensing, 2020

ABSTRACT Differential interferogram of space-borne SAR data may be affected by residual orbital f... more ABSTRACT Differential interferogram of space-borne SAR data may be affected by residual orbital fringes resulting from errors in the orbit (i.e. baseline) determination that hinder subsequent InSAR applications (deformation or elevation measurements). In this paper, an easy-to-use method was developed to remove the orbit errors in complex SAR interferogram in the radar coordinate system by accurately estimating the frequencies of the orbital ramp phase. The method first finds an approximate integer frequency by searching for the peak of the sum of the Fourier spectra of all the rows of the interferogram. It then uses the 100-order Burg spectral estimation algorithm to estimate the power spectrum for each row of the interferogram, and calculates the high-resolution power spectrum over the frequency range Hz. Finally, the method obtains the exact frequency of the orbital ramp phase in the row direction by searching for the peak of the sum of the high-resolution power spectra of all rows. By performing the same operations on all columns of the interferogram, the exact frequency in the column direction can be obtained. The orbital ramp phase can be calculated using these exact frequencies and be removed from the interferogram. Validation tests demonstrate that our method can accurately estimate the frequencies of the orbital ramp phase in the row and column directions, and eliminate the orbital ramp fringes from the simulated and actual interferograms. The proposed method only needs to calculate the high-resolution spectrum in a small frequency range, so the burden of calculation is light. The proposed method is easy to use since phase unwrapping or a priori satellite orbit information is not required.

International Journal of Remote Sensing, 2019

The 2016 M w 5.9 Menyuan earthquake occurred on the Qilian-Haiyuan fault system on the northeaste... more The 2016 M w 5.9 Menyuan earthquake occurred on the Qilian-Haiyuan fault system on the northeastern margin of the Tibetan Plateau. Since the seismogenic source is a blind fault, it is difficult to obtain reliable geometric parameters of the source only from the satellite data. In this paper, we used two aftershock relocation data sets to constrain the seismogenic fault, and obtained two southwest-dipping listric fault models with a strike of about 126°and different dip angles. According to the geological structures, we assumed that the dip is uniformly reduced along the width direction, and modelled the Interferometric Synthetic Aperture Radar (InSAR) data of the Menyuan event using a simulated annealing algorithm to search for the optimal fault dips. The optimal top and bottom dips are about 59°and 1°, respectively. Using the optimal fault model, we obtained the slip distribution and three-dimensional displacement fields for the 2016 M w 5.9 Menyuan earthquake. Sliding occurs mainly on the four sub-faults in the middle of the model, indicating that the rupture zone is relatively small. The displacement fields indicate that the seismogenic source is a thrust fault, and the epicentre experienced a strong northeastward compression deformation.

Seismological Research Letters, 2018

Journal of Geodesy, 2018

We used both seismic and InSAR data to investigate the mechanism behind the 2011 Hawthorne (Nevad... more We used both seismic and InSAR data to investigate the mechanism behind the 2011 Hawthorne (Nevada) earthquake swarm that occurred between March 15 and August 17, 2011. Regional seismic data were used to estimate the centroid depth and focal mechanism for nine earthquakes that occurred in this swarm, with magnitudes between M w 3.9 and M w 4.8. The inferred focal mechanisms indicate that the source of these earthquakes is normal faulting with a small left-lateral strike-slip component along the southwest direction. Three InSAR displacement maps covering the epicentral zone of the 2011 Hawthorne earthquakes were inverted to get a slip model. The slip distribution shows that the deformation source is characterized by normal faulting, consistent with our inferred focal mechanisms. Our results suggest that the seismogenic zone was in the tensile stress environment. The temporal and spatial evolutions of seismicity suggest that the 2011 Hawthorne swarm might be caused by aseismic slip. Therefore, the 2011 Hawthorne earthquake swarm may have been the result of aseismic slip under the regional tectonic stress, and had nothing to do with volcanic activity. However, the quantitative evidence for aseismic slip is limited to the indication that the geodetic moment is 15% greater than the seismic moment, which is near the level of uncertainty.

Journal of Asian Earth Sciences, 2017

The 2015 M w 7:8 Nepal earthquake occurred on the segment of the main Himalayan thrust fault betw... more The 2015 M w 7:8 Nepal earthquake occurred on the segment of the main Himalayan thrust fault between the Indian and Eurasian plates, and caused serious casualties. This earthquake may produce a profound impact on the evolution of the Tibetan Plateau and have brought a stress loading to faults within the plateau. In this paper, a high-resolution slip distribution of the 2015 Nepal earthquake is inverted from the InSAR and GPS data in the near field, and is used to compute the evolution of the cumulative Coulomb stress changes on faults in the earthquake-prone zone in the Tibetan Plateau. In the given reasonable parameters, the calculated co-and post-seismic stress changes on faults do not exceed 1.0 kPa at the north of latitude 32°in the Tibetan Plateau. The largest positive stress changes occur on the South Tibet Detachment fault, and the magnitudes are much less than 100 kPa. The estimated seismicity rate change on the segment of the South Tibet Detachment fault can be up to a level of two hundred thousandths. This indicates that there is a high hazard of earthquake triggering in the South Tibet Detachment fault and its adjacent regions. In the northern and eastern Tibetan Plateau, the estimated seismicity rate changes are lower than a level of one thousandth. However, some faults with a relative high background seismicity rate, such as the Xianshuihe and Longmenshan faults, may have a high hazard of earthquake triggering in the future.

Journal of Asian Earth Sciences, 2015

We invert the background stress fields of the Longmenshan and its adjacent regions before and aft... more We invert the background stress fields of the Longmenshan and its adjacent regions before and after the 2008 great Wenchuan earthquake from focal mechanism data. Our results show that the stress orientations after the 2008 great Wenchuan earthquake are more coherent than those before this event at the epicentral zone. This result includes twofold implications: one is that the Wenchuan event altered the local stress field, the other is that the strength of the Wenchuan fault zone is very high and the characteristic of the seismogenic fault is consistent with the asperity model. We also estimate the stress changes caused by the Wenchuan event using an accurate source model and exhaustive receiver faults. The stress changes of >10 kPa mainly occur in the nearby areas of the Longriba, east Kunlun, Qingchuan, Lushan faults and the southeastern section of the Xianshuihe fault, indicating that there is high earthquake hazard in these areas. The seismicity before and after the great Wenchuan earthquake in the Longmenshan and its adjacent regions shows that some subsequent earthquakes in the stress shadow area may be delayed and the 2013 Lushan earthquake may be advanced.

Remote Sensing of the Environment: 16th National Symposium on Remote Sensing of China, 2008

... 1). We process the five pairs using three-pass interferometric method by the Doris InSAR soft... more ... 1). We process the five pairs using three-pass interferometric method by the Doris InSAR software5 and obtain the interferograms containing topographical information (See Fig.2). It is noticeable that the image pair (3 Dec. 2003, 7 Jan. ...

Journal of Asian Earth Sciences, 2013

Abstract The 2003 M w 6.3 Delingha earthquake happened at the Dacaidan-Zongwulong fault system, w... more Abstract The 2003 M w 6.3 Delingha earthquake happened at the Dacaidan-Zongwulong fault system, which is an important active tectonic belt on the northeastern margin of Tibetan plateau. Until the end of 2004, 6 approximately M w 5.0 aftershocks occurred on almost the same seismogenic fault. The conventional viewpoint is that the seismic hazard near the continental seismogenic fault will be reduced in decades or centuries after rupture. Why did so many large earthquakes happen on almost the same seismogenic fault within a short temporal interval? The seismogenic fault information and the character of the co-seismic slip distribution are the keys to answer this problem. In this paper, the co-seismic slip distribution of the 2003 M w 6.3 Delingha earthquake was inverted using 18 teleseismic broadband P waveforms, 8 SH waveforms and 28 long period surface waveforms data. The peak slip concentrates at 12 km depth beneath the epicenter, and the slip decreases gradually from 6 km depth to surface and beneath 12 km depth. The shallow slip deficit of the co-seismic slip distribution may be caused by inelastic failures in the uppermost crust. Beneath 12 km depth, the strain energy may be accumulated by the velocity-strengthening frition behavior and may trigger aftershock. Three post-seismic InSAR interferograms spanning the most aftershocks were formed. Through analysis on the aftershock distribution and the focal mechanisms of M w ⩾ 4.9 aftershocks, two 3D finite element models containing topography were built and used to simulate the InSAR observations. Comparing the modeled results with the InSAR observations, we obtained the seismic source of the 2003–2004 Delingha earthqakes. It consists of two southwest-dipping seismogenic faults, named the west-fault and the east-fault. The east-fault extends beneath the west-fault. The 2003 M w 6.3 Delingha earthquake occurred on the west-fault, while 6 large aftershocks occurred on the east-fault. This shows that the complex spatial location relationship between the seismogenic faults may be an important factor to the large earthquake occurrence with high frequency at almost the same locality. Due to special tectonic setting and complex structure, the Dacaidan-Zongwulong fault system will be a high seismic risk zone in the future.

IEEE Geoscience and Remote Sensing Letters, 2008

A novel noise reduction scheme for synthetic aperture radar (SAR) interferograms based on the wav... more A novel noise reduction scheme for synthetic aperture radar (SAR) interferograms based on the wavelet packet transform (WPT) and the Wiener filter is introduced in this letter. First, by employing the WPT in the spatial frequency domain, the real and imaginary parts of the complex noisy interferogram are decomposed, respectively, and the wavelet coefficients are obtained. Then, for these coefficients, Wiener filtering is adopted to remove noise. This scheme can filter noise adaptively according to the local noise level, without requiring any a priori information. By using a simulated noisy interferogram and two ENVISAT advanced synthetic aperture radar C-band interferograms, the performance of this scheme, in terms of noise reduction and fringes preservation, is reported and compared with other filter algorithms. The experimental results demonstrate the effectiveness of the proposed scheme.

IEEE Geoscience and Remote Sensing Letters, 2012

An accurate phase unwrapping algorithm is presented for reconstructing the true phase field for d... more An accurate phase unwrapping algorithm is presented for reconstructing the true phase field for deformation interferograms. This algorithm is a combination of reliability sorting and residue mask, while introducing more reliable unwrapping fiducial information. In tests conducted with a pyramidal phase image, a complex simulated interferogram, and a real deformation interferogram, the proposed algorithm successfully unwraps the images with perfect precision. This algorithm is also shown to be superior to the prevailing improved Goldstein's residue-cut algorithm in terms of precision.

Acta Seismologica Sinica, 2007

Using seismic shear phases from 47 Tonga-Fiji and its adjacent region events recorded by the CENC... more Using seismic shear phases from 47 Tonga-Fiji and its adjacent region events recorded by the CENC and IRIS, and from 26 northeast Asia and north Pacific events recorded by IRIS, we studied the shear wave anisotropy in D” region beneath the western Pacific utilizing the ScS-S differential travel time method and obtained the splitting time values between the radial and transverse components of each ScS wave corresponding to each core-mantle boundary (CMB) reflection point. We found that most shear waves involved horizontally polarized shear wave components traveling faster than vertically polarized shear wave components through the D” region. The splitting time values of ScS wave range from −0.91 s to 3.21 s with an average value of 1.1 s. The strength of anisotropy varies from −0.45% to 1.56% with an average value of 0.52%. The observations and analyses show that in the D” region beneath the western Pacific the lateral flow is expected to be dominant and the vertical transverse isotropy may be the main anisotropic structure. This structure feature may be explained by the shape preferred orientation of the CMB chemical reaction products or partial melt and the lattice preferred orientation of the lower mantle materials caused by the lateral flow at lowermost mantle.

Acta Seismologica Sinica, 2005

ABSTRACT

Acta Seismologica Sinica, 2006

... Vol.19 554 )( )() 22 22 2 z ad v g zWa D Θ = − α (2) where v is viscosity, d is distance betw... more ... Vol.19 554 )( )() 22 22 2 z ad v g zWa D Θ = − α (2) where v is viscosity, d is distance between upper and lower boundaries of this system, a is thermal expansion, the operator D=d/dz and dimensionless wave number a2=(dkx)2+(dky)2= 2 2 y x a a + . ...

Acta Seismologica Sinica, 2008

Modeling transient and long-term postseismic deformation: A case study of 1995 M W 9.5 Chile eart... more Modeling transient and long-term postseismic deformation: A case study of 1995 M W 9.5 Chile earthquake * SHAO Zhi-gang (邵志刚) FU Rong-shan (傅容珊) XUE Ting-xiao (薛廷虓) ZHA Xian-jie (查显杰)

Acta Seismologica Sinica, 2005

Upper mantle convection driving by density anomaly and a test model* FU Rong-shan ((~.~) WANG Jin... more Upper mantle convection driving by density anomaly and a test model* FU Rong-shan ((~.~) WANG Jing-yun (q:~..~) CHANG Xiao-hua (~:~) HUANG Jian-hua (~.~~) DAI Zhi-yang (~ gff) ZHA Xian-jie (~,~)

Earthquake Science, 2011

We use interferometric synthetic aperture radar (InSAR) and broadband seismic waveform data to es... more We use interferometric synthetic aperture radar (InSAR) and broadband seismic waveform data to estimate a source model of the 11th July, 2004 MW6.2 Zhongba earthquake, Tibet of China. This event occurred within the seismically active zone of southwestern Tibetan Plateau where the east-west extension of the upper crust is observed. Because of limitations in one pair of InSAR data available, there are trade-offs among centroid depth, rupture area and amount of slip. Available seismic data tightly constrain the focal mechanism and centroid depth of the earthquake but not the horizontal location. Together, two complementary data sets can be used to identify the actual fault plane, better constrain the slip model and event location. We first use regional seismic waveform to estimate point source mechanism, then InSAR data is used to obtain better location. Finally, a joint inversion of teleseismic P-waves and InSAR data is performed to obtain a distributed model. Our preferred point source mechanism indicates a seismic moment of ∼2.2×10 18 N•m (∼MW6.2), a fault plane solution of 171 • (342 •)/42 • (48 •)/−83 • (−97 •), corresponding to strike/dip/rake, and a depth of 11 km. The fault plane with strike of 171 • and dip of 42 • is identified as the ruptured fault with the aid of InSAR data. The preferred source model features compact area of slips between depth of 5-11 km and 10 km along strike with maximum slip amplitude of about 1.5 m.

Bulletin of the Seismological Society of America, 2011

We construct a coseismic deformation interferogram for the April 2010 Yushu earthquakes using ALO... more We construct a coseismic deformation interferogram for the April 2010 Yushu earthquakes using ALOS/PALSAR data from the ascending track (path 487). We then infer the trace of the Yushu fault using the coherence image, and we build five fault models for the Yushu fault. To determine the fault geometry parameters that give the best fit to the coseismic interferogram, we apply an elastic dislocation algorithm. Our preferred fault model consists of two faults dipping to the northeast. One strikes ∼N60°W with a dip of 82°; the other strikes ∼N67°W with a dip of 86°. Lastly, we infer the coseismic slip distributions of the Yushu earthquakes by the inversion of the displacement in the line of sight (LOS). The results show that three high-slip concentrations are located at a depth of 5 ∼ 8 km, with a peak slip of 1.32 m at (96.93 E, 33.03 N). The Yushu fault is a left-lateral strike-slip faulting with small northside-up, dip-slip components.

Geophysical Journal International, 2009

The 1999 M s = 5.6 Kuqa earthquake occurred in a seismically active belt between the Tianshan Mou... more The 1999 M s = 5.6 Kuqa earthquake occurred in a seismically active belt between the Tianshan Mountain and the Traim basin. Because of the sparse seismic network and complex crustal structure, it is very difficult to accurately locate the epicentre for this event using seismic waves. The epicentres located by different research groups vary over a spatial range of 20-40 km. Interferometric synthetic aperture radar (InSAR) is a geodetic technique with fine spatial resolution, good precision and wide coverage. An interferometric map of the epicentral region constrains the epicentre of this event. The arid climate and sparsely vegetation in the Kuqa region provide excellent conditions for InSAR studies. In this paper, we firstly construct a interferogram to map the coseismic deformation field due to the 1999 Kuqa earthquake using a coseismic interferometric pair of radar images acquired by the ESA ERS-2 satellite. Then, we develop a new geocoding method and apply it to the interferogram. Next, we infer the geometry of the seismogenic fault according to its focal mechanism and tectonic setting. To model the interferogram, we assume a dislocation buried in a uniform elastic half-space. Finally, we infer the epicentre of this earthquake to be located at (82.80 • E, 41.92 • N), which is close to the results of the National Earthquake Information Center of USGS and China Earthquake Administration. The epicentre location inferred from InSAR falls in the six-level isoseismal contour described by Xinjiang earthquake administration using the field investigations.

In the past two decades, dental implants have been an essential component of the public health. H... more In the past two decades, dental implants have been an essential component of the public health. However, lack of a reliable and safe dental surgery imaging modality remains a major problem. Optical coherence tomography (OCT) is an interferometic optical imaging modality that is somewhat similar to B-mode ultrasound but utilizes infrared light instead of sound waves. It can provide optical biopsy at a very high resolution and in real time. The compact fiber-optic components of OCT make it easy to integrate into dental drill bit to provide the dentists with real-time image feedback about the anatomical structure in the vicinity of the drill bit. This research focuses on the image processing for such a concept designing OCT integrated dental drilling system. Various image processing methods are applied to the OCT images with the intention of finding out the suitable solutions for speckle noise reduction, image reconstruction and dental tissues segmentation. OCT imaging system obtains the cross sectional structure of samples by measuring the back reflected light. The coherent detection makes the OCT images are always subject to speckle noise. The existence of speckle noise limits the interpretation of OCT images. In this study, various speckle reduction digital filters are applied to the images obtained from OCT during high speed rotation. Our results indicate that the adaptive Wiener filter is particularly suitable for our specific application. It is a time–saving method that not only significantly suppresses speckle noise but also preserves image edges. The study also concerns the image restoration due to the non-uniform rotational scanning. One modified method based on the cross correlation between successive A-scans is posted and studied. The assembled images indicate our algorithm is capable of reconstructing the manually-scanned images with an acceptable assemble accuracy. In tissue segmentation, the porous structure of the trabecular bones enables us to discriminate different them from cortical bones. However, due to the intensity decay along the depth direction, the way for image automatic segmentation is still a major problem need to be solved in future research. To test and verify our algorithms, the experiments are conducted to both real animal jawbones and silicone elastomer-based optical tissue phantoms. This proof-of-concept study shows that OCT is able to probe dental tissues in rotational scanning. The results from both samples are highly in accord with each other. This conclusion suggests that our optical phantom is a good jawbone substitute. The durable, easy-to-make phantoms can significantly reduce the cost of future researches.

Bulletin of the Seismological Society of America

The hidden Haicheng fault system is an earthquake-prone zone on the Liaodong Peninsula, China. It... more The hidden Haicheng fault system is an earthquake-prone zone on the Liaodong Peninsula, China. Its seismogenic structure is still unclear and needs further study. In this study, we used the differential evolution algorithm to invert the waveform data of the 2008 ML 4.8 Haicheng earthquake and the 2012 ML 4.8 Gaizhou earthquake and obtained an updated 1D crustal velocity model. The model reveals a low-velocity zone with a depth of 18–24 km below the Haicheng fault zone. Based on the velocity model, we used the arrival-time data to accurately locate the earthquakes that occurred in the Haicheng area from 2008 to 2018. The relocated earthquakes show that the Az 300°-trending Haicheng fault consists of two segments spaced about 2 km apart, namely the western and the eastern segments. They are about 12 and 22 km long and inclined to the northeast with dips of 70° and 80°, respectively. These seismogenic structures of the Haicheng fault zone are important for assessing the future seismic ...

International Journal of Remote Sensing, 2020

ABSTRACT Differential interferogram of space-borne SAR data may be affected by residual orbital f... more ABSTRACT Differential interferogram of space-borne SAR data may be affected by residual orbital fringes resulting from errors in the orbit (i.e. baseline) determination that hinder subsequent InSAR applications (deformation or elevation measurements). In this paper, an easy-to-use method was developed to remove the orbit errors in complex SAR interferogram in the radar coordinate system by accurately estimating the frequencies of the orbital ramp phase. The method first finds an approximate integer frequency by searching for the peak of the sum of the Fourier spectra of all the rows of the interferogram. It then uses the 100-order Burg spectral estimation algorithm to estimate the power spectrum for each row of the interferogram, and calculates the high-resolution power spectrum over the frequency range Hz. Finally, the method obtains the exact frequency of the orbital ramp phase in the row direction by searching for the peak of the sum of the high-resolution power spectra of all rows. By performing the same operations on all columns of the interferogram, the exact frequency in the column direction can be obtained. The orbital ramp phase can be calculated using these exact frequencies and be removed from the interferogram. Validation tests demonstrate that our method can accurately estimate the frequencies of the orbital ramp phase in the row and column directions, and eliminate the orbital ramp fringes from the simulated and actual interferograms. The proposed method only needs to calculate the high-resolution spectrum in a small frequency range, so the burden of calculation is light. The proposed method is easy to use since phase unwrapping or a priori satellite orbit information is not required.

International Journal of Remote Sensing, 2019

The 2016 M w 5.9 Menyuan earthquake occurred on the Qilian-Haiyuan fault system on the northeaste... more The 2016 M w 5.9 Menyuan earthquake occurred on the Qilian-Haiyuan fault system on the northeastern margin of the Tibetan Plateau. Since the seismogenic source is a blind fault, it is difficult to obtain reliable geometric parameters of the source only from the satellite data. In this paper, we used two aftershock relocation data sets to constrain the seismogenic fault, and obtained two southwest-dipping listric fault models with a strike of about 126°and different dip angles. According to the geological structures, we assumed that the dip is uniformly reduced along the width direction, and modelled the Interferometric Synthetic Aperture Radar (InSAR) data of the Menyuan event using a simulated annealing algorithm to search for the optimal fault dips. The optimal top and bottom dips are about 59°and 1°, respectively. Using the optimal fault model, we obtained the slip distribution and three-dimensional displacement fields for the 2016 M w 5.9 Menyuan earthquake. Sliding occurs mainly on the four sub-faults in the middle of the model, indicating that the rupture zone is relatively small. The displacement fields indicate that the seismogenic source is a thrust fault, and the epicentre experienced a strong northeastward compression deformation.

Seismological Research Letters, 2018

Journal of Geodesy, 2018

We used both seismic and InSAR data to investigate the mechanism behind the 2011 Hawthorne (Nevad... more We used both seismic and InSAR data to investigate the mechanism behind the 2011 Hawthorne (Nevada) earthquake swarm that occurred between March 15 and August 17, 2011. Regional seismic data were used to estimate the centroid depth and focal mechanism for nine earthquakes that occurred in this swarm, with magnitudes between M w 3.9 and M w 4.8. The inferred focal mechanisms indicate that the source of these earthquakes is normal faulting with a small left-lateral strike-slip component along the southwest direction. Three InSAR displacement maps covering the epicentral zone of the 2011 Hawthorne earthquakes were inverted to get a slip model. The slip distribution shows that the deformation source is characterized by normal faulting, consistent with our inferred focal mechanisms. Our results suggest that the seismogenic zone was in the tensile stress environment. The temporal and spatial evolutions of seismicity suggest that the 2011 Hawthorne swarm might be caused by aseismic slip. Therefore, the 2011 Hawthorne earthquake swarm may have been the result of aseismic slip under the regional tectonic stress, and had nothing to do with volcanic activity. However, the quantitative evidence for aseismic slip is limited to the indication that the geodetic moment is 15% greater than the seismic moment, which is near the level of uncertainty.

Journal of Asian Earth Sciences, 2017

The 2015 M w 7:8 Nepal earthquake occurred on the segment of the main Himalayan thrust fault betw... more The 2015 M w 7:8 Nepal earthquake occurred on the segment of the main Himalayan thrust fault between the Indian and Eurasian plates, and caused serious casualties. This earthquake may produce a profound impact on the evolution of the Tibetan Plateau and have brought a stress loading to faults within the plateau. In this paper, a high-resolution slip distribution of the 2015 Nepal earthquake is inverted from the InSAR and GPS data in the near field, and is used to compute the evolution of the cumulative Coulomb stress changes on faults in the earthquake-prone zone in the Tibetan Plateau. In the given reasonable parameters, the calculated co-and post-seismic stress changes on faults do not exceed 1.0 kPa at the north of latitude 32°in the Tibetan Plateau. The largest positive stress changes occur on the South Tibet Detachment fault, and the magnitudes are much less than 100 kPa. The estimated seismicity rate change on the segment of the South Tibet Detachment fault can be up to a level of two hundred thousandths. This indicates that there is a high hazard of earthquake triggering in the South Tibet Detachment fault and its adjacent regions. In the northern and eastern Tibetan Plateau, the estimated seismicity rate changes are lower than a level of one thousandth. However, some faults with a relative high background seismicity rate, such as the Xianshuihe and Longmenshan faults, may have a high hazard of earthquake triggering in the future.

Journal of Asian Earth Sciences, 2015

We invert the background stress fields of the Longmenshan and its adjacent regions before and aft... more We invert the background stress fields of the Longmenshan and its adjacent regions before and after the 2008 great Wenchuan earthquake from focal mechanism data. Our results show that the stress orientations after the 2008 great Wenchuan earthquake are more coherent than those before this event at the epicentral zone. This result includes twofold implications: one is that the Wenchuan event altered the local stress field, the other is that the strength of the Wenchuan fault zone is very high and the characteristic of the seismogenic fault is consistent with the asperity model. We also estimate the stress changes caused by the Wenchuan event using an accurate source model and exhaustive receiver faults. The stress changes of >10 kPa mainly occur in the nearby areas of the Longriba, east Kunlun, Qingchuan, Lushan faults and the southeastern section of the Xianshuihe fault, indicating that there is high earthquake hazard in these areas. The seismicity before and after the great Wenchuan earthquake in the Longmenshan and its adjacent regions shows that some subsequent earthquakes in the stress shadow area may be delayed and the 2013 Lushan earthquake may be advanced.

Remote Sensing of the Environment: 16th National Symposium on Remote Sensing of China, 2008

... 1). We process the five pairs using three-pass interferometric method by the Doris InSAR soft... more ... 1). We process the five pairs using three-pass interferometric method by the Doris InSAR software5 and obtain the interferograms containing topographical information (See Fig.2). It is noticeable that the image pair (3 Dec. 2003, 7 Jan. ...

Journal of Asian Earth Sciences, 2013

Abstract The 2003 M w 6.3 Delingha earthquake happened at the Dacaidan-Zongwulong fault system, w... more Abstract The 2003 M w 6.3 Delingha earthquake happened at the Dacaidan-Zongwulong fault system, which is an important active tectonic belt on the northeastern margin of Tibetan plateau. Until the end of 2004, 6 approximately M w 5.0 aftershocks occurred on almost the same seismogenic fault. The conventional viewpoint is that the seismic hazard near the continental seismogenic fault will be reduced in decades or centuries after rupture. Why did so many large earthquakes happen on almost the same seismogenic fault within a short temporal interval? The seismogenic fault information and the character of the co-seismic slip distribution are the keys to answer this problem. In this paper, the co-seismic slip distribution of the 2003 M w 6.3 Delingha earthquake was inverted using 18 teleseismic broadband P waveforms, 8 SH waveforms and 28 long period surface waveforms data. The peak slip concentrates at 12 km depth beneath the epicenter, and the slip decreases gradually from 6 km depth to surface and beneath 12 km depth. The shallow slip deficit of the co-seismic slip distribution may be caused by inelastic failures in the uppermost crust. Beneath 12 km depth, the strain energy may be accumulated by the velocity-strengthening frition behavior and may trigger aftershock. Three post-seismic InSAR interferograms spanning the most aftershocks were formed. Through analysis on the aftershock distribution and the focal mechanisms of M w ⩾ 4.9 aftershocks, two 3D finite element models containing topography were built and used to simulate the InSAR observations. Comparing the modeled results with the InSAR observations, we obtained the seismic source of the 2003–2004 Delingha earthqakes. It consists of two southwest-dipping seismogenic faults, named the west-fault and the east-fault. The east-fault extends beneath the west-fault. The 2003 M w 6.3 Delingha earthquake occurred on the west-fault, while 6 large aftershocks occurred on the east-fault. This shows that the complex spatial location relationship between the seismogenic faults may be an important factor to the large earthquake occurrence with high frequency at almost the same locality. Due to special tectonic setting and complex structure, the Dacaidan-Zongwulong fault system will be a high seismic risk zone in the future.

IEEE Geoscience and Remote Sensing Letters, 2008

A novel noise reduction scheme for synthetic aperture radar (SAR) interferograms based on the wav... more A novel noise reduction scheme for synthetic aperture radar (SAR) interferograms based on the wavelet packet transform (WPT) and the Wiener filter is introduced in this letter. First, by employing the WPT in the spatial frequency domain, the real and imaginary parts of the complex noisy interferogram are decomposed, respectively, and the wavelet coefficients are obtained. Then, for these coefficients, Wiener filtering is adopted to remove noise. This scheme can filter noise adaptively according to the local noise level, without requiring any a priori information. By using a simulated noisy interferogram and two ENVISAT advanced synthetic aperture radar C-band interferograms, the performance of this scheme, in terms of noise reduction and fringes preservation, is reported and compared with other filter algorithms. The experimental results demonstrate the effectiveness of the proposed scheme.

IEEE Geoscience and Remote Sensing Letters, 2012

An accurate phase unwrapping algorithm is presented for reconstructing the true phase field for d... more An accurate phase unwrapping algorithm is presented for reconstructing the true phase field for deformation interferograms. This algorithm is a combination of reliability sorting and residue mask, while introducing more reliable unwrapping fiducial information. In tests conducted with a pyramidal phase image, a complex simulated interferogram, and a real deformation interferogram, the proposed algorithm successfully unwraps the images with perfect precision. This algorithm is also shown to be superior to the prevailing improved Goldstein's residue-cut algorithm in terms of precision.

Acta Seismologica Sinica, 2007

Using seismic shear phases from 47 Tonga-Fiji and its adjacent region events recorded by the CENC... more Using seismic shear phases from 47 Tonga-Fiji and its adjacent region events recorded by the CENC and IRIS, and from 26 northeast Asia and north Pacific events recorded by IRIS, we studied the shear wave anisotropy in D” region beneath the western Pacific utilizing the ScS-S differential travel time method and obtained the splitting time values between the radial and transverse components of each ScS wave corresponding to each core-mantle boundary (CMB) reflection point. We found that most shear waves involved horizontally polarized shear wave components traveling faster than vertically polarized shear wave components through the D” region. The splitting time values of ScS wave range from −0.91 s to 3.21 s with an average value of 1.1 s. The strength of anisotropy varies from −0.45% to 1.56% with an average value of 0.52%. The observations and analyses show that in the D” region beneath the western Pacific the lateral flow is expected to be dominant and the vertical transverse isotropy may be the main anisotropic structure. This structure feature may be explained by the shape preferred orientation of the CMB chemical reaction products or partial melt and the lattice preferred orientation of the lower mantle materials caused by the lateral flow at lowermost mantle.

Acta Seismologica Sinica, 2005

ABSTRACT

Acta Seismologica Sinica, 2006

... Vol.19 554 )( )() 22 22 2 z ad v g zWa D Θ = − α (2) where v is viscosity, d is distance betw... more ... Vol.19 554 )( )() 22 22 2 z ad v g zWa D Θ = − α (2) where v is viscosity, d is distance between upper and lower boundaries of this system, a is thermal expansion, the operator D=d/dz and dimensionless wave number a2=(dkx)2+(dky)2= 2 2 y x a a + . ...

Acta Seismologica Sinica, 2008

Modeling transient and long-term postseismic deformation: A case study of 1995 M W 9.5 Chile eart... more Modeling transient and long-term postseismic deformation: A case study of 1995 M W 9.5 Chile earthquake * SHAO Zhi-gang (邵志刚) FU Rong-shan (傅容珊) XUE Ting-xiao (薛廷虓) ZHA Xian-jie (查显杰)

Acta Seismologica Sinica, 2005

Upper mantle convection driving by density anomaly and a test model* FU Rong-shan ((~.~) WANG Jin... more Upper mantle convection driving by density anomaly and a test model* FU Rong-shan ((~.~) WANG Jing-yun (q:~..~) CHANG Xiao-hua (~:~) HUANG Jian-hua (~.~~) DAI Zhi-yang (~ gff) ZHA Xian-jie (~,~)

Earthquake Science, 2011

We use interferometric synthetic aperture radar (InSAR) and broadband seismic waveform data to es... more We use interferometric synthetic aperture radar (InSAR) and broadband seismic waveform data to estimate a source model of the 11th July, 2004 MW6.2 Zhongba earthquake, Tibet of China. This event occurred within the seismically active zone of southwestern Tibetan Plateau where the east-west extension of the upper crust is observed. Because of limitations in one pair of InSAR data available, there are trade-offs among centroid depth, rupture area and amount of slip. Available seismic data tightly constrain the focal mechanism and centroid depth of the earthquake but not the horizontal location. Together, two complementary data sets can be used to identify the actual fault plane, better constrain the slip model and event location. We first use regional seismic waveform to estimate point source mechanism, then InSAR data is used to obtain better location. Finally, a joint inversion of teleseismic P-waves and InSAR data is performed to obtain a distributed model. Our preferred point source mechanism indicates a seismic moment of ∼2.2×10 18 N•m (∼MW6.2), a fault plane solution of 171 • (342 •)/42 • (48 •)/−83 • (−97 •), corresponding to strike/dip/rake, and a depth of 11 km. The fault plane with strike of 171 • and dip of 42 • is identified as the ruptured fault with the aid of InSAR data. The preferred source model features compact area of slips between depth of 5-11 km and 10 km along strike with maximum slip amplitude of about 1.5 m.

Bulletin of the Seismological Society of America, 2011

We construct a coseismic deformation interferogram for the April 2010 Yushu earthquakes using ALO... more We construct a coseismic deformation interferogram for the April 2010 Yushu earthquakes using ALOS/PALSAR data from the ascending track (path 487). We then infer the trace of the Yushu fault using the coherence image, and we build five fault models for the Yushu fault. To determine the fault geometry parameters that give the best fit to the coseismic interferogram, we apply an elastic dislocation algorithm. Our preferred fault model consists of two faults dipping to the northeast. One strikes ∼N60°W with a dip of 82°; the other strikes ∼N67°W with a dip of 86°. Lastly, we infer the coseismic slip distributions of the Yushu earthquakes by the inversion of the displacement in the line of sight (LOS). The results show that three high-slip concentrations are located at a depth of 5 ∼ 8 km, with a peak slip of 1.32 m at (96.93 E, 33.03 N). The Yushu fault is a left-lateral strike-slip faulting with small northside-up, dip-slip components.

Geophysical Journal International, 2009

The 1999 M s = 5.6 Kuqa earthquake occurred in a seismically active belt between the Tianshan Mou... more The 1999 M s = 5.6 Kuqa earthquake occurred in a seismically active belt between the Tianshan Mountain and the Traim basin. Because of the sparse seismic network and complex crustal structure, it is very difficult to accurately locate the epicentre for this event using seismic waves. The epicentres located by different research groups vary over a spatial range of 20-40 km. Interferometric synthetic aperture radar (InSAR) is a geodetic technique with fine spatial resolution, good precision and wide coverage. An interferometric map of the epicentral region constrains the epicentre of this event. The arid climate and sparsely vegetation in the Kuqa region provide excellent conditions for InSAR studies. In this paper, we firstly construct a interferogram to map the coseismic deformation field due to the 1999 Kuqa earthquake using a coseismic interferometric pair of radar images acquired by the ESA ERS-2 satellite. Then, we develop a new geocoding method and apply it to the interferogram. Next, we infer the geometry of the seismogenic fault according to its focal mechanism and tectonic setting. To model the interferogram, we assume a dislocation buried in a uniform elastic half-space. Finally, we infer the epicentre of this earthquake to be located at (82.80 • E, 41.92 • N), which is close to the results of the National Earthquake Information Center of USGS and China Earthquake Administration. The epicentre location inferred from InSAR falls in the six-level isoseismal contour described by Xinjiang earthquake administration using the field investigations.