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ArticleAges and magnetic structures of the South China Sea constrained by deep tow magnetic surveys and IODP Expedition 349(John Wiley & Sons, 2014-12-27) Li, Chun-Feng ; Xu, Xing ; Lin, Jian ; Sun, Zhen ; Zhu, Jian ; Yao, Yongjian ; Zhao, Xixi ; Liu, Qingsong ; Kulhanek, Denise K. ; Wang, Jian ; Song, Taoran ; Zhao, Junfeng ; Qiu, Ning ; Guan, Yongxian ; Zhou, Zhiyuan ; Williams, Trevor ; Bao, Rui ; Briais, Anne ; Brown, Elizabeth A. ; Chen, Yifeng ; Clift, Peter D. ; Colwell, Frederick S. ; Dadd, Kelsie A. ; Ding, Weiwei ; Almeida, Ivan Hernandez ; Huang, Xiao-Long ; Hyun, Sangmin ; Jiang, Tao ; Koppers, Anthony A. P. ; Li, Qianyu ; Liu, Chuanlian ; Liu, Zhifei ; Nagai, Renata H. ; Peleo-Alampay, Alyssa ; Su, Xin ; Tejada, Maria Luisa G. ; Trinh, Hai Son ; Yeh, Yi-Ching ; Zhang, Chuanlun ; Zhang, Fan ; Zhang, Guo-LiangCombined analyses of deep tow magnetic anomalies and International Ocean Discovery Program Expedition 349 cores show that initial seafloor spreading started around 33 Ma in the northeastern South China Sea (SCS), but varied slightly by 1–2 Myr along the northern continent-ocean boundary (COB). A southward ridge jump of ∼20 km occurred around 23.6 Ma in the East Subbasin; this timing also slightly varied along the ridge and was coeval to the onset of seafloor spreading in the Southwest Subbasin, which propagated for about 400 km southwestward from ∼23.6 to ∼21.5 Ma. The terminal age of seafloor spreading is ∼15 Ma in the East Subbasin and ∼16 Ma in the Southwest Subbasin. The full spreading rate in the East Subbasin varied largely from ∼20 to ∼80 km/Myr, but mostly decreased with time except for the period between ∼26.0 Ma and the ridge jump (∼23.6 Ma), within which the rate was the fastest at ∼70 km/Myr on average. The spreading rates are not correlated, in most cases, to magnetic anomaly amplitudes that reflect basement magnetization contrasts. Shipboard magnetic measurements reveal at least one magnetic reversal in the top 100 m of basaltic layers, in addition to large vertical intensity variations. These complexities are caused by late-stage lava flows that are magnetized in a different polarity from the primary basaltic layer emplaced during the main phase of crustal accretion. Deep tow magnetic modeling also reveals this smearing in basement magnetizations by incorporating a contamination coefficient of 0.5, which partly alleviates the problem of assuming a magnetic blocking model of constant thickness and uniform magnetization. The primary contribution to magnetic anomalies of the SCS is not in the top 100 m of the igneous basement.
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ArticleMechanism of progressive broad deformation from oceanic transform valley to off-transform faulting and rifting(Elsevier, 2022-01-25) Zhang, Fan ; Lin, Jian ; Zhou, Zhiyuan ; Yang, Hongfeng ; Morgan, Jason P.Oceanic transform faults (TFs) are commonly viewed as single, narrow strike-slip seismic faults that offset two mid-ocean ridge segments. However, broad zones of complex deformation are ubiquitous at TFs. Here, we propose a new conceptual model for the progressive deformation within broad zones at oceanic TFs through detailed morphological, seismic, and stress analyses. We argue that, under across-transform extension due to a change in plate motion, plate deformation occurs first along high-angle transtensional faults (TTFs) within the transform valleys. Off-transform normal faults (ONFs) form when across-transform deviatoric extensional stresses exceed the yield strength of the adjacent oceanic lithosphere. With further extension, these normal faults can develop into off-transform rift zones (ORZs), some of which can further develop into transform plate boundaries. We illustrate that such progressive complex deformation is an inherent feature of oceanic TFs. The new conceptual model provides a unifying theory to explain the observed broad deformation at global transform systems.
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ArticleMechanism of the 2017 M-w 6.3 Pasni earthquake and its significance for future major earthquakes in the eastern Makran(Oxford University Press, 2022-07-05) Yang, Xiaodong ; Qiu, Qiang ; Feng, Wanpeng ; Lin, Jian ; Zhang, Jinchang ; Zhou, Zhiyuan ; Zhang, FanMakran subduction zone is very active with ∼38 mm yr−1 convergence rate and has experienced great earthquakes in the past. The latest great earthquake of 1945 Mw 8.1 event also triggered a large tsunami and led to ∼4000 casualties. However, due to incomplete historical seismicity records and poor modern instrumentation, earthquake mechanism, co-seismic slip and tsunami characteristics in Makran remain unclear. On 2017 February 17, an Mw 6.3 earthquake rattled offshore Pasni of Pakistan in the eastern Makran, marking the largest event after the 1945 Mw 8.1 earthquake with good geodetic and geophysical data coverage. We use a combination of seismicity, multibeam bathymetry, seismic profile, InSAR measurements and tide-gauge observation to investigate the seismogenic structure, co-seismic deformation, tsunami characteristics of this event and its implication for future major earthquakes. Our results indicate that (1) the earthquake occurred on the shallow-dipping (3°–4°) megathrust; (2) the megathrust co-seismically slipped 15 cm and caused ∼2–4 cm ground subsidence and uplift at Pasni; (3) our tsunami modelling reproduces the observed 5-cm-high small tsunami waveforms. The Pasni earthquake rupture largely overlaps the 1945 slip patch and disturbs the west and east megathrust segments that have not ruptured yet at least since 1765. With such stress perturbation and possible stress evolution effect from the 1945 earthquake, the unruptured patches may fail in the future. This study calls for more preparedness in mitigating earthquake and associated hazards in the eastern Makran.
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ArticleSeismic stratigraphy of the central South China Sea basin and implications for neotectonics(John Wiley & Sons, 2015-03-16) Li, Chun-Feng ; Li, Jiabiao ; Ding, Weiwei ; Franke, Dieter ; Yao, Yongjian ; Shi, Hesheng ; Pang, Xiong ; Cao, Ying ; Lin, Jian ; Kulhanek, Denise K. ; Williams, Trevor ; Bao, Rui ; Briais, Anne ; Brown, Elizabeth A. ; Chen, Yifeng ; Clift, Peter D. ; Colwell, Frederick S. ; Dadd, Kelsie A. ; Hernandez-Almeida, Ivan ; Huang, Xiao-Long ; Hyun, Sangmin ; Jiang, Tao ; Koppers, Anthony A. P. ; Li, Qianyu ; Liu, Chuanlian ; Liu, Qingsong ; Liu, Zhifei ; Nagai, Renata H. ; Peleo-Alampay, Alyssa ; Su, Xin ; Sun, Zhen ; Tejada, Maria Luisa G. ; Trinh, Hai Son ; Yeh, Yi-Ching ; Zhang, Chuanlun ; Zhang, Fan ; Zhang, Guo-Liang ; Zhao, XixiCoring/logging data and physical property measurements from International Ocean Discovery Program Expedition 349 are integrated with, and correlated to, reflection seismic data to map seismic sequence boundaries and facies of the central basin and neighboring regions of the South China Sea. First-order sequence boundaries are interpreted, which are Oligocene/Miocene, middle Miocene/late Miocene, Miocene/Pliocene, and Pliocene/Pleistocene boundaries. A characteristic early Pleistocene strong reflector is also identified, which marks the top of extensive carbonate-rich deposition in the southern East and Southwest Subbasins. The fossil spreading ridge and the boundary between the East and Southwest Subbasins acted as major sedimentary barriers, across which seismic facies changes sharply and cannot be easily correlated. The sharp seismic facies change along the Miocene-Pliocene boundary indicates that a dramatic regional tectonostratigraphic event occurred at about 5 Ma, coeval with the onsets of uplift of Taiwan and accelerated subsidence and transgression in the northern margin. The depocenter or the area of the highest sedimentation rate switched from the northern East Subbasin during the Miocene to the Southwest Subbasin and the area close to the fossil ridge in the southern East Subbasin in the Pleistocene. The most active faulting and vertical uplifting now occur in the southern East Subbasin, caused most likely by the active and fastest subduction/obduction in the southern segment of the Manila Trench and the collision between the northeast Palawan and the Luzon arc. Timing of magmatic intrusions and seamounts constrained by seismic stratigraphy in the central basin varies and does not show temporal pulsing in their activities.
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ArticleIntra- and intertrench variations in flexural bending of the Manila, Mariana and global trenches : implications on plate weakening in controlling trench dynamics(Oxford University Press, 2017-11-08) Zhang, Fan ; Lin, Jian ; Zhou, Zhiyuan ; Yang, Hongfeng ; Zhan, WenhuanWe conducted detailed analyses of a global array of trenches, revealing systematic intra- and intertrench variations in plate bending characteristics. The intratrench variations of the Manila and Mariana Trenches were analysed in detail as end-member cases of the relatively young (16–36 Ma) and old (140–160 Ma) subducting plates, respectively. Meanwhile, the intertrench variability was investigated for a global array of additional trenches including the Philippine, Kuril, Japan, Izu-Bonin, Aleutian, Tonga-Kermadec, Middle America, Peru, Chile, Sumatra and Java Trenches. Results of the analysis show that the trench relief (W0) and width (X0) of all systems are controlled primarily by the faulting-reduced elastic thickness near the trench axis (Tme) and affected only slightly by the initial unfaulted thickness (TMe) of the incoming plate. The reduction in Te has caused significant deepening and narrowing of trench valleys. For the cases of relatively young or old plates, the plate age could be a dominant factor in controlling the trench bending shape, regardless the variations in axial loadings. Our calculations also show that the axial loading and stresses of old subducting plates can vary significantly along the trench axis. In contrast, the young subducting plates show much smaller values and variations in axial loading and stresses.
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PreprintVariations in oceanic plate bending along the Mariana trench( 2014-05) Zhang, Fan ; Lin, Jian ; Zhan, WenhuanWe quantify along-trench variations in plate flexural bending along the Mariana trench in the western Pacific Ocean. A 3-D interpreted flexural deformation surface of the subducting Pacific Plate was obtained by removing from the observed bathymetry the effects of sediment loading, isostatically-compensated topography based on gravity modeling, age-related lithospheric thermal subsidence, and residual short-wavelength features. We analyzed flexural bending of 75 across-trench profile sections and calculated five best-fitting tectonic and plate parameters that control the flexural bending. Results of analysis revealed significant along-trench variations: the trench relief varies from 0.9 to 5.7 km, trench-axis vertical loading (-V0) from -0.73 × 1012 to 3.17 × 1012 N/m, and axial bending moment (-M0) from 0.1 × 1017 to 2.7× 1017 N. The effective elastic plate thickness seaward of the outer-rise region (Te M) ranges from 45 to 52 km, while that trench-ward of the outer-rise (Te m) ranges from 19 to 40 km. This corresponds to a reduction in Te of 21-61%. The transition from Te M to Te m occurs at a breaking distance of 60-125 km from the trench axis, which is near the outer-rise and corresponds to the onset of observed pervasive normal faults. The Challenger Deep area is associated with the greatest trench relief and axial vertical loading, while areas with seamounts at the trench axis are often associated with more subtle trench relief, smaller axial vertical loading, and greater topographic bulge at the outer-rise.