Zheng
Tingting
Zheng
Tingting
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ArticleLong-term evolution of nontransform discontinuities at the Mid-Atlantic Ridge, 24°N–27°30′N(American Geophysical Union, 2019-09-11) Zheng, Tingting ; Tucholke, Brian E. ; Lin, JianWe studied long‐term evolution of nontransform discontinuities (NTDs) on the Mid‐Atlantic Ridge from 0‐ to ~20‐ to 25‐Ma crust using plate reconstructions of multibeam bathymetry, long‐range HMR1 sidescan sonar, residual mantle Bouguer gravity anomaly (RMBA), and gravity‐derived crustal thickness. NTDs have propagated north and south with respect to flowlines of relative plate motion and both rapidly and slowly compared to the half spreading rate; at times they have been quasi‐stable. Fast, short‐term (<2 Myr) propagation is driven by reduced magma supply (increased tectonic extension) in the propagating ridge tip when NTD ridge‐axis offsets are small (≲5 km). Propagation at larger offsets generally is slower and longer term. These NTDs can show classic structures of rift propagation including inner and outer pseudofaults and crustal blocks transferred between ridge flanks by discontinuous jumps of the propagating ridge tip. In all cases crustal transfer occurs within the NTD valley. Aside from ridge‐axis offset, the evolution of NTDs appears to be controlled by three factors: (1) gross volume and distribution of magma supplied to ridge segments as controlled by 3‐D heterogeneities in mantle fertility and/or dynamic upwelling; this controls fundamental ridge segmentation. (2) The lithospheric plumbing system through which magma is delivered to the crust. (3) The consequent focusing of tectonic extension in magma‐poor parts of spreading segments, typically at segment ends, which can drive propagation. We also observe long‐wavelength (5‐10 Myr) RMBA asymmetry between the conjugate ridge flanks, and we attribute this to asymmetric distribution of density anomalies in the upper mantle.
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ArticleGravity anomalies and implications for shallow mantle processes of the western Cocos‐Nazca spreading center(American Geophysical Union, 2023-03-02) Zheng, Tingting ; Lin, Jian ; Schouten, Hans ; Smith, Deborah K. ; Klein, Emily ; Parnell‐Turner, RossThis study analyzes up‐to‐date gravity data in the Galapagos triple junction region to understand crustal structure and melt distribution beneath the propagating Cocos‐Nazca spreading center (CNSC). Application of a standard thermal model to the mantle Bouguer gravity anomaly (MBA) does not appear to result in a realistic crustal thickness in this region. The cross‐CNSC MBA profiles flatten and axial values increase from east toward the western end of the CNSC. A simple smoothing filter applied to the standard thermal model with different filter widths can explain the progressive flattening of the MBA and is interpreted as different distribution widths (concentrations) of partial melt in the mantle. The east‐west residual MBA gradient along the CNSC is similar to the east flank of the East Pacific Rise (EPR), suggesting that the along‐CNSC gradient could partly reflect the shallow mantle properties associated with the EPR.
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ArticleRaised potential earthquake and tsunami hazards at the North Sulawesi subduction zone after a flurry of major seismicity(Elsevier, 2022-11-30) Zheng, Tingting ; Qiu, Qiang ; Lin, Jian ; Yang, XiaodongThe North Sulawesi subduction zone (NSSZ) was ruptured by a series of large earthquakes (Mw >7) since 1990s, generally triggered small to moderate tsunamis in the surrounding seas and ocean. But the 2018 Sulawesi Mw 7.5 earthquake ruptured the west subduction zone and induced a large tsunami that displaced hundreds of people. These large earthquakes, especially the deeper thrust events, generated stress loading to the shallow megathrust that could rupture to excite exceptional tsunami hazard as observed in Sumatra, Japan and the other subduction zones. Whether the stress loading from downdip events can trigger future failure of a shallow tsunami earthquake and its ensuring tsunami hazard impact remains elusive. Here we investigate the potential of earthquake and tsunami by analyzing the historical earthquake characteristics, calculating Coulomb stress changes and simulating hundreds of hypothetical earthquake ruptures to assess the plausible tsunami hazard in the NSSZ. Our results show that a series of Mw 7+ downdip megathrust earthquakes have loaded most of the megathrust, especially the shallow portion (<10 km), with increased stress >10 kPa, implicating a high potential of future large earthquakes and ensuring outsize tsunamis. Our modeled tsunami wave heights vary between >0 and 43 m along the North Sulawesi coastlines. One intriguing fact is that the end point of the tsunami wave energy dissipation path gains a comparable tsunami impact as the region in the rupture zone for all the magnitude considered, highlighting a dual-pattern threatened regions in the Celebes Sea. Importantly, the thrust and fold belt structure in the wide outer wedge of the accretionary prism and the strong seafloor bathymetry variation offshore Sulawesi Island could serve an efficient wave-amplification tool that need to be considered in future hazard assessment. Our findings alert that the earthquake and tsunami hazard potential are largely raised by these downdip major earthquakes.
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DatasetLong-Term evolution of non-transform discontinuities at the Mid-Atlantic Ridge, 24°N - 27°30′N( 2018-12) Zheng, Tingting ; Tucholke, Brian E. ; Lin, JianWe studied long-term evolution of non-transform discontinuities (NTDs) on the Mid-Atlantic Ridge from 0 to ~20-25 Ma crust using plate reconstructions of multibeam bathymetry, long-range HMR1 sidescan sonar, residual mantle Bouguer gravity anomaly, and gravity-derived crustal thickness. NTDs have propagated north and south with respect to flowlines of relative plate motion and both rapidly and slowly compared to the half spreading rate, and at times they have been quasi-stable. Fast, short-term (<2 m.y.) propagation is driven by reduced magma supply (increased extension) in the propagating ridge tip when NTD ridge-axis offsets are small (<~ 5 km). Slow propagation can be much longer term. Some NTDs show classic structures of rift propagation including inner and outer pseudofaults and crustal blocks transferred between ridge flanks by discontinuous jumps of the propagating ridge tip. In all cases crustal transfer occurs within the NTD valley. Aside from ridge-axis offset, the evolution of NTDs appears to be controlled by three factors: (1) Gross volume and distribution of magma supplied to ridge segments as controlled by 3D heterogeneities in mantle fertility and/or dynamic upwelling; this controls fundamental ridge segmentation. (2) The lithospheric plumbing system through which magma is delivered to the crust. (3) The consequent focusing of tectonic extension in magma-poor parts of spreading segments, typically at segment ends, which can drive propagation. We also observe long-wavelength (5-10 m.y.) RMBA asymmetry between the conjugate ridge flanks, and we attribute this to asymmetric distribution of density anomalies in the upper mantle.