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| 1 | A shallow aftershock sequence in the north-eastern end of the Wenchuan earthquake aftershock zone显示文摘Previous studies show that mature faults are filled with fault gouge in the shallow part and thus cannot accumulate enough strain energy for earthquakes. Therefore most earthquakes are deeper than 5 km, except those events occurring on new faults or in intact rocks. From field observation, Wenchuan earthquake is found to rupture the free surface about 200 km, but the rupture may extend underground much further from teleseismic body waves inversion and aftershocks distribution. In the northeastern end of the rupture zone, deep rupture may induce stress increase near the free surface, and trigger shallow earthquakes. An Ms 5.7 aftershock occurred at Qingchuan, northeast end of Wenchuan earthquake fault on July 24, 2008, featuring thrust mechanism with a 3 km source centroid depth. The shallow focal depth is confirmed with the sPL phase recorded at station L0205. As Rayleigh wave is well only developed for source depth less than 1/5 of epicentral distance, the observed large amplitude of Rg at a distance of 15 km implied depth of 3 km or less. Dozens of aftershocks' sPL waveforms are also analyzed to confirm the source depths less than 3 km. On the other hand, no surface ruptures are found by geological survey or InSAR studies. It is strongly suggested that these aftershock sequences initiate fresh rupture in intact rocks triggered by stress increase from the deep co-seismic rupture of the Wenchuan mainshock. | Luo Yan Ni SiDao Zeng XiangFang Zheng Yong Chen QiFu Chen Yong | 2010 | Science China Earth Sciences2010，53，11： | 26 |
| 2 | The M5.0 Suining-Tongnan (China) earthquake of 31 January 2010:A destructive earthquake occurring in sedimentary cover显示文摘Usually, only crystalline basement is strong enough to store the massive strain energy that can be released in a damaging earthquake. By contrast, sedimentary cover is weak, because of its relatively high porosity and fluids. Therefore, it generally cannot accumulate enough energy for strong earthquakes. On January 31, 2010, a M5.0 earthquake occurred near the border of Suining and Tongnan in China. It excited strong short-period Rayleigh waves Rg, indicative of its shallow focal depth. The focal depth is constrained to less than 4 km, most probably in the range of 1-3 km, by modeling amplitude dependence on the frequency and waveforms of teleseismic depth phases (pP, sP). Because the local Mesozoic sedimentary cover is about 6 km thick, this earthquake should have occurred in the sedimentary cover. Though some shallow earthquakes with magnitudes up to M4 occur in Paleozoic sediments, this earthquake is the first M5 event studied in Mesozoic sedimentary cover. This event provides a rare opportunity to study seismogenic processes of damaging earthquakes in sedimentary basins. | LUO Yan NI SiDao ZENG XiangFang XIE Jun CHEN Yong LONG Feng | 2011 | Chinese Science Bulletin2011，56，6： | 17 |
| 3 | Determination of focal depth by two waveform-based methods:A case study for the 2008 Panzhihua earthquake显示文摘With the 2008 M S 6.1 Panzhihua earthquake as a case study,we demonstrate that the focal depth of the main shock can be well constrained with two approaches:(1) using the depth phase sPL and (2) using full waveform inversion of local and teleseismic data.We also show that focal depths can be well constrained using the depth phase sPL with single broadband seismic station.Our study indicates that the main shock is located at a depth of 11 km,much shallower than those from other studies,confirming that the earthquake occurs in upper crust.Aftershocks are located in the depth range of 11-16 km,which is consistent with a ruptured near vertical fault whose width is about 10 km,as expected for an M S 6.1 earthquake. | Zhenjie Wang Jiajun Chong Sidao Ni Barbara Romanowicz | 2011 | Earthquake Science2011，24，4： | 17 |
| 4 | Rupture directivity of the August 3rd, 2014 Ludian earthquake(Yunan, China)显示文摘An M6.5 earthquake occurred on August 3rd, 2014 in Ludian of Yunnan Province in China, causing severe casualty and economic loss. Local broadband waveform inversion with the CAP method demonstrates that the earthquake is a strike-slip event, with the strike along 70° and 160° for the two nodal planes respectively. However, the geological structure in the epicentral region is complicated with abundant active faults, and it is challenging to identify the seismogenic fault with the focal plane solutions due to nodal-plane ambiguity. We resolved the rupture directivity by measuring the difference between centroid location and hypocenter of the Ludian earthquake with the time shift from CAP inversion, and found that the nodal plane with the strike of 160° is the ruptured fault plane. Moreover, the rupture is found to propagate from northwest to southeast. | HE XiaoHui NI SiDao LIU Jie | 2015 | Science China Earth Sciences2015，58，5： | 12 |
| 5 | Slip model for the 2011 M_w 9.0 Sendai (Japan) earthquake and its M_w 7.9 aftershock derived from GPS data显示文摘用为 8 h 的测量 GPS 的 coseismic 和 seismic 以后排水量跟随 M w 2011 年 3 月 11 日, coseismic 和 seismic 以后差错的 9.0 仙台地震滑动模型基于一个分层的外壳的模型被开发。主要吃惊的测地学的时刻大小是被测量近似 M w 8.98。slip 展出清楚的反向的特征,与大约 23.3 m 的 hypocenter,和大小附近的最大值。某罢工滑倒行为可以发生在山峰破裂地区的二个方面上。主要吃惊释放的几乎 90% 地震时刻发生在深度不到 40 km。精力由差错释放了在跟随主要吃惊的 8 h 滑倒近似等于 M w 的地震 8.13。与 1.5 m 的最大值, seismic 以后滑倒在 coseismic 破裂差错的西南的部分被集中,它与 M w 的地点和行为同意很好 7.9 余震。这暗示在在主要吃惊以后的 8 h 的 seismic 以后变丑被 M w 主要导致 7.9 余震。另外, seismic 以后 0.20.4 m 滑倒在 coseismic 破裂的下面剧降延期被观察,它可能被在滑倒以后的效果在这个时期期间引起了。 | DIAO FaQi XIONG Xiong NI SiDao ZHENG Yong GE Can | 2011 | Chinese Science Bulletin2011，56，27： | 8 |
| 6 | Near surface velocity and Q_s structure of the Quaternary sediment in Bohai basin,China显示文摘Heavily populated by Beijing and Tianjin cities,Bohai basin is a seismically active Cenozoic basin suffering from huge lost by devastating earthquakes,such as Tangshan earthquake.The attenuation(QP and QS) of the surficial Quaternary sediment has not been studied at natural seismic frequency(1-10 Hz),which is crucial to earthquake hazards study.Borehole seismic records of micro earthquake provide us a good way to study the velocity and attenuation of the surficial structure(0-500 m).We found that there are two pulses well separated with simple waveforms on borehole seismic records from the 2006 MW4.9 Wen'an earthquake sequence.Then we performed waveform modeling with generalized ray theory(GRT) to confirm that the two pulses are direct wave and surface reflected wave,and found that the average vP and vS of the top 300 m in this region are about 1.8 km/s and 0.42 km/s,leading to high vP/vS ratio of 4.3.We also modeled surface re-flected wave with propagating matrix method to constrain QS and the near surface velocity structure.Our modeling indicates that QS is at least 30,or probably up to 100,much larger than the typically assumed extremely low Q(~10),but consistent with QS modeling in Mississippi embayment.Also,the velocity gradient just beneath the free surface(0-50 m) is very large and velocity increases gradually at larger depth.Our modeling demonstrates the importance of borehole seismic records in resolving shallow velocity and attenuation structure,and hence may help in earthquake hazard simulation. | Jiajun Chong Sidao Ni | 2009 | Earthquake Science2009，22，5： | 7 |
| 7 | Composition of high frequency ambient noise from cross-correlation:A case study using a small aperture array显示文摘Long-time cross correlation of ambient noise has been proved as a powerful tool to extract Green's function between two receivers.The study of composition of ambient noise is important for a better understanding of this method.Previous studies confirm that ambient noise in the long period (3 s and longer) mostly consists of surface wave,and 0.25-2.5 s noise consists more of body waves.In this paper,we perform cross correlation processing at much higher frequency (30-70 Hz) using ambient noise recorded by a small aperture array.No surface waves emerge from noise correlation function (NCF),but weak P waves emerge.The absence of surface wave in NCF is not due to high attenuation since surface waves are strong from active source,therefore probably the high ambient noise mostly consists of body wave and lacks surface wave.Origin of such high frequency body waves in ambient noise remains to be studied. | Weitao Wang Sidao Ni Baoshan Wang | 2010 | Earthquake Science2010，23，5： | 6 |
| 8 | Rapid earthquake focal mechanism inversion using high-rate GPS velometers in sparse network显示文摘In this study, we demonstrate an approach for inverting earthquake source parameters based on high-rate global positioning system(GPS) velocity seismograms. The velocity records obtained from single-station GPS velocity solutions with broadcast ephemeris are used directly for earthquake source parameter inversion using the Cut and Paste method, without requiring conversion of the velocity records into displacement records. Taking the El Mayor-Cucapah earthquake as an example, GPS velocity records from 10 stations with reasonable azimuthal coverage provide earthquake source parameters very close to those from the Global centroid moment tensor(Global CMT) solution. In sparse network tests, robust source parameters with acceptable bias can be achieved with as few as three stations. When the number of stations is reduced to two, the bias in rake angle becomes appreciable, but the magnitude and strike estimations are still robust. The results of this study demonstrate that rapid and reliable estimation of earthquake source parameters can be obtained from GPS velocity data. These parameters could be used for early earthquake warning and shake map construction, because such GPS velocity records can be obtained in real time. | GUO AiZhi NI SiDao CHEN WeiWen Jeffrey T.FREYMUELLER SHEN ZhiChao | 2015 | Science China Earth Sciences2015，58，11： | 3 |
| 9 | Source model of the 11th July 2004 Zhongba earthquake revealed from the joint inversion of InSAR and seismological data显示文摘We use interferometric synthetic aperture radar (InSAR) and broadband seismic waveform data to estimate a source model of the 11th July, 2004 M W 6.2 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 (~M W 6.2), 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. | Shengji Wei Sidao Ni Xianjie Zha Don Helmberger | 2011 | Earthquake Science2011，24，2： | 3 |
| 10 | Magnitude and rupture duration from high frequency teleseismic P wave with projected landweber deconvolution显示文摘Earthquake magnitude and rupture duration are among the most important parameters characterizing an earthquake for the purpose of early tsunami warning. While they can be routinely determined from broadband P waveforms with iterative inver- sion procedures, the inversion procedures may fail when the rupture either lasts longer than the interval between P and later arrivals or requires too much time or human intervention. Little contaminated by later arrivals, high frequency P waves are useful for modeling earthquake source processes, though the envelope waveform is affected by strong scattering in lithosphere. With high frequency envelopes from aftershocks as Empirical Green's Function (EGF), the coda effects can be removed and more accurate relative source time function (RSTF) of the main shock can be obtained. Assuming that RSTFs cannot be negative, we use the projected Landweber deconvolution method (PLD) to obtain high frequency RSTFs because PLD method has the advantage of non-negativity, causality, and compactness (finite duration). We are able to determine rupture durations of four large earthquakes: the 2004 Sumatra-Andaman earthquake, the 2005 Nias event, the 2006 Java event, and the 2011 Tokuko earthquake. The rupture durations of the Sumatra-Andaman, Nias, and Tohuko events are found to be around 550, 110, and 120 s respectively, consistent with previous studies. The rupture duration of the Java event is about 130 s, supporting that the Java event is a tsunami earthquake. The magnitudes of these earthquakes are found to depend on both the amplitude and the duration of the deconvolved waveforms, and can be approximated by integrating these waveforms. | ZHENG Yong NI SiDao CHEN Yong TAN Ying Don HELMBERGER | 2013 | Science China Earth Sciences2013，56，1： | 3 |
| 11 | Crustal S-wave velocity structure of the Yellowstone region using a seismic ambient noise method显示文摘The Yellowstone volcano is one of the largest active volcanoes in the world,and its potential hazards demand detailed seismological and geodetic studies.Previous studies with travel time tomography and receiver functions have revealed a low-velocity layer in the crust beneath the Yellowstone volcano,suggesting the presence of a magma chamber at depth.We use ambient seismic noise from regional seismic stations to retrieve short-period surface waves and then study the shallow shear velocity structure of the Yellowstone region by surface wave dispersion analysis.We first obtained a crustal model of the area outside of the Yellowstone volcano and then constructed an absolute shear wave velocity structure in combination with receiver function results for the crust beneath the Yellowstone volcano.The velocity model shows a low-velocity layer with shear velocity at around1.3 km/s,suggesting that a large-scale magma chamber exists at shallow levels within the crust of the Yellowstone volcanic region. | Yan Lü Sidao Ni Jun Xie Yingjie Xia Xiangfang Zeng Bin Liu | 2013 | Earthquake Science2013，26，5： | 2 |
| 12 | Stationary phase approximation in the ambient noise method revisited显示文摘The method of extracting Green's function between stations from cross correlation has proven to be effective theoretically and experimentally.It has been widely applied to surface wave tomography of the crust and upmost mantle.However,there are still controversies about why this method works.Snieder employed stationary phase approximation in evaluating contribution to cross correlation function from scatterers in the whole space,and concluded that it is the constructive interference of waves emitted by the scatterers near the receiver line that leads to the emergence of Green's function.His derivation demonstrates that cross correlation function is just the convolution of noise power spectrum and the Green's function.However,his derivation ignores influence from the two stationary points at infinities,therefore it may fail when attenuation is absent.In order to obtain accurate noise-correlation function due to scatters over the whole space,we compute the total contribution with numerical integration in polar coordinates.Our numerical computation of cross correlation function indicates that the incomplete stationary phase approximation introduces remarkable errors to the cross correlation function,in both amplitude and phase,when the frequency is low with reasonable quality factor Q.Our results argue that the distance between stations has to be beyond several wavelengths in order to reduce the influence of this inaccuracy on the applications of ambient noise method,and only the station pairs whose distances are above several (>5) wavelengths can be used. | Zhongwen Zhan Sidao Ni | 2010 | Earthquake Science2010，23，5： | 2 |
| 13 | Seismic attenuation in the lower mantle beneath Northeast China constrained from short-period reflected core phases at short epicentral distances显示文摘The thermal structure of the lower mantle plays a key role in understanding the dynamic processes of the Earth's evolution and mantle convection.Because intrinsic attenuation in the lower mantle is highly sensitive to temperature,determining of the attenuation of the lower mantle could help us determine its thermal state.We attempted to constrain the attenuation of the lower mantle by measuring the amplitude ratios of p to ScP on the vertical component and s to ScS on the tangential component at short epicentral distances for seismic wave data from deep earthquakes in Northeast China.We calculated the theoretical amplitude ratios of p to ScP and s to ScS by using ray theory and the axial-symmetric spectral element method AxiSEM,as well as by considering the effects of radiation patterns,geometrical spreading,and ScP reflection coefficients.By comparing the observed amplitude ratios with the synthetic results,we constrained the quality factors as Qα≈3,000 and Qβ≈1,300 in the lower mantle beneath Northeast China,which are much larger than those in the preliminary reference Earth model(PREM)model of Qα~800 and Qβ~312.We propose that the lower mantle beneath Northeast China is relatively colder than the average mantle,resulting in weaker intrinsic attenuation and higher velocity.We estimated the temperature of the lower mantle beneath Northeast China as approximately 300–700 K colder than the global average value. | BaoLong Zhang SiDao Ni YuLin Chen | 2019 | Earth and Planetary Physics2019，3，6： | 2 |
| 14 | An Adaptive 2D Planar Projection and Its Application in Geoscience Studies显示文摘A linear projection approach is developed to present geoscience research result in planar coordinate system projected from spherical coordinate system. Here, the sphere is intersected by a plane and its surface is projected onto the plane. In order to keep the projected coordinate system orthogonal, and minimize the distortion, one axis of the planar coordinate system is chosen in our projection based on the shape of the region to be projected, and the other axes can be chosen arbitrarily or based on the constraint of the orthogonality. In the new method the projection is self-contained. The forward projection can be fully projected backward without loss of precision. The central area of the sphere will be projected to the planar system without distortion, and the latitudinal length in the rotated spherical system keeps constant during the projecting process. Only the longitudinal length in the rotated spherical system changes with the rotated latitude. The distortion of the projection therefore, overall, is small and suitable for geoscience studies. | Yong Zheng Bikai Jin Xiong Xiong Sidao Ni | 2015 | Journal of Earth Science2015，26，5： | 1 |
| 15 | Magnitude estimation for early warning applications using the initial part of P waves: A case study on the 2008 Wenchuan sequence显示文摘 | Wang Weitao Ni Sidao Chen Yong Kanamori Hiroo | 2009 | Geophysical Research Letters2009，，16： | 1 |
| 16 | Sharp sides to the African superplume显示文摘 | Ni Sidao Tan Eh Gurnis Michael and Helmberger Don | 2002 | Science2002，296，： | 1 |
| 17 | Further constraints on the African superplume structure 显示文摘 | Ni Sidao and Helmberger Don V | 2003 | Physics of the Earth and Planetary Interiors2003，，： | 1 |
| 18 | Seismological constraints on the South African superplume; could be the oldest distinct structure on Earth显示文摘 | Ni Sidao and Helmberger Don V | 2003 | Earth and Planetary Science Letters2003，206，： | 1 |
| 19 | Further constraints on the African superplume structure显示文摘 | Sidao N Helmberger D V | 2003 | Phys Earth Planet Inter2003，140，： | 1 |
| 20 | A Case Study on the Effect of Post-critical SmS on Ground Motion in Yingjiang,Yunnan Province,China显示文摘There are controversies on ground motion attenuation relations at the epicentral distance of about 100km. Some models predict that the seismic energy remains almost constant or becomes even stronger with increasing distance at this distance,while other models hold that it decreases with increased distance. The divergence lies mainly in whether SmS is stronger than direct S and surface waves at this distance. With the MS5. 9 earthquake sequence in the Yingjiang region of Yunnan Province as an example,we demonstrate that SmS is always 2 ~ 5 times stronger than direct S waves around the epicentral distance of 100km ( which is the post-critical distance for S in this region ). Study of synthetic seismograms suggest that crustal structure has an important effect on the amplitude of post-critical SmS, with simple crust producing strong SmS. This preliminary study confirms that in China,SmS also plays an important role on ground motion at distances around 100km,which demands more studies of post-critical SmS. | Luo Yan Ni Sidao Chen Yong | 2011 | Earthquake Research in China2011，25，1： | 0 |
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