Gong Jianhua

No Thumbnail Available
Last Name
Gong
First Name
Jianhua
ORCID
0000-0002-0485-5108

Filters

2019 - 2019 3 2020 - 2021 2
5
Reset filters

Settings

Search Results

Now showing 1 - 5 of 5
  • Article
    Causes of oceanic crustal thickness oscillations along a 74-M Mid-Atlantic ridge flow line
    (American Geophysical Union, 2019-11-19) Shinevar, William J. ; Mark, Hannah F. ; Clerc, Fiona ; Codillo, Emmanuel A. ; Gong, Jianhua ; Olive, Jean-Arthur ; Brown, Stephanie M. ; Smalls, Paris T. ; Liao, Yang ; Le Roux, Véronique ; Behn, Mark D.
    Gravity, magnetic, and bathymetry data collected along a continuous 1,400‐km‐long spreading‐parallel flow line across the Mid‐Atlantic Ridge indicate significant tectonic and magmatic fluctuations in the formation of oceanic crust over a range of time scales. The transect spans from 28 Ma on the African Plate to 74 Ma on the North American plate, crossing the Mid‐Atlantic Ridge at 35.8°N. Gravity‐derived crustal thicknesses vary from 3–9 km with a standard deviation of 1.0 km. Spectral analysis of bathymetry and residual mantle Bouguer anomaly show a diffuse power at >1 Myr and concurrent peaks at 390, 550, and 950 kyr. Large‐scale (>10 km) mantle thermal and compositional heterogeneities, variations in upper mantle flow, and detachment faulting likely generate the >1 Myr diffuse power. The 550‐ and 950‐kyr peaks may reflect the presence of magma solitons and/or regularly spaced ~7.7 and 13.3 km short‐wavelength mantle compositional heterogeneities. The 390‐kyr spectral peak corresponds to the characteristic spacing of faults along the flow line. Fault spacing also varies over longer periods (>10 Myr), which we interpret as reflecting long‐lived changes in the fraction of tectonically versus magmatically accommodated extensional strain. A newly discovered off‐axis oceanic core complex (Kafka Dome) found at 8 Ma on the African plate further suggests extended time periods of tectonically‐dominated plate separation. Fault spacing negatively correlates with gravity‐derived crustal thickness, supporting a strong link between magma input and fault style at mid‐ocean ridges.
  • Technical Report
    AT42-20 Cruise Report for the 2019-2021 Gofar Transform Fault Earthquake Prediction Experiment, Leg 1: OBS Deployment and Rock Dredging
    (Woods Hole Oceanographic Institution, 2019-12) Warren, Jessica M. ; Behn, Mark D. ; Fan, Wenyuan ; Morrow, Thomas ; Prigent, Cécile ; Schwartz, Darin M. ; Andrys, Janine ; Bahruth, Melinda ; Gong, Jianhua ; Lin, Kuan-Yu ; Gardner, Alan T. ; Kot, Dan ; Rapa, Martin ; Kelly, Brian ; A'Hearn, Patrick ; Warren, Jessica
    The goal of this cruise was to deploy 51 ocean bottom seismometers (OBS) and conduct rock dredges at the Quebrada/Discovery/Gofar (QDG) transform fault systems, with a focus on the Gofar system. QDG is located in the equatorial east Pacific on the East Pacific Rise (Figure 1). Sections of the Gofar and Discovery systems rupture with large (Mw > 5.3) earthquakes every 5-6 years, while only one event of this size has occurred on Quebrada in the last 35 years. Variations in along-strike earthquake behavior during these seismic cycles are further constrained by results from a 2008 OBS experiment on QDG. The 2008 experiment revealed the presence of ‘rupture zones’, which fail quasi-periodically in M6 earthquakes, and ‘rupture barriers’, which repeatedly stop large ruptures, yet undergo intense foreshock sequences. The current OBS deployment on Gofar is thus aimed at recording variations in stress build up, stress release, and fault strength within the context of a well-known seismic cycle.
  • Article
    Constraints on the geometry of the subducted Gorda Plate from converted phases generated by local earthquakes
    (American Geophysical Union, 2021-01-25) Gong, Jianhua ; McGuire, Jeffrey J.
    The largest slip in great megathrust earthquakes often occurs in the 10–30 km depth range, yet seismic imaging of the material properties in this region has proven difficult. We utilize a dense onshore‐offshore passive seismic dataset from the southernmost Cascadia subduction zone where seismicity in the mantle of the subducted Gorda Plate produces S‐to‐P and P‐to‐S conversions generated within a few km of the plate interface. These conversions typically occur in the 10–20 km depth range at either the top or bottom of a ∼5 km thick layer with a high Vp/Vs that we infer to be primarily the subducted crust. We use their arrival times and amplitudes to infer the location of the top and bottom of the subducted crust as well as the velocity contrasts across these discontinuities. Comparing with both the Slab1.0 and the updated Slab2 interface models, the Slab2 model is generally consistent with the converted phases, while the Slab1.0 model is 1–2 km deeper in the 2–20 km depth range and ∼6–8 km too deep in the 10–20 km depth range between 40.25°N and 40.4°N. Comparing the amplitudes of the converted phases to synthetics for simplified velocity structures, the amplitude of the converted phases requires models containing a ∼5 km thick zone with at least a ∼10%–20% reduction in S wave velocity. Thus, the plate boundary is likely contained within or at the top of this low velocity zone, which potentially indicates a significant porosity and fluid content within the seismogenic zone.
  • Thesis
    Structure and mechanics of the subducted Gorda plate: constrained by afterslip simulations and scattered seismic waves
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2021-02) Gong, Jianhua ; McGuire, Jeffrey J. ; Lizarralde, Daniel
    Subduction zones host the greatest earthquakes on earth and pose great threat to human society. The largest slip in megathrust earthquakes often occurs in the 10–50 km depth range, yet seismic imaging of the material properties in this region has proven difficult. This thesis focuses on developing methods to utilize high frequency (2–12 Hz) seismic waves scattered from the megathrust plate interface to constrain its fine-scale velocity structures and to investigate the relationship between velocity structures and megathrust slip behaviors. Chapter 2 investigates the locking condition of the subducted Gorda plate by simulating afterslip that would be expected as a result of the stress changes from offshore strike-slip earthquakes. Chapter 3 develops array analysis methods to identify P-to-S and S-to-P seismic converted phases that convert at the subducted Gorda plate interface from local earthquakes and uses them to constrain the geometry and material properties of the plate boundary fault of the subducted Gorda plate between 5–20 km depth. Chapters 4 and 5 use a dense nodal array and numerical modeling methods to study the seismic guided waves that propagate along the thin low velocity layer at the boundary of the subducted Gorda plate. Taken together, our results indicate that material properties of the subduction plateboundary fault is highly heterogeneous and the plate-boundary fault is potentially contained in a low velocity layer with significant porosity and fluid content at seismogenic depths.
  • Dataset
    Causes of oceanic crustal thickness oscillations along a 74-Myr Mid-Atlantic Ridge flow line
    ( 2019-11-12) Shinevar, William J. ; Mark, Hannah F. ; Clerc, Fiona ; Codillo, Emmanuel A. ; Gong, Jianhua ; Olive, Jean-Arthur ; Brown, Stephanie M. ; Smalls, Paris T. ; Liao, Yang ; Le Roux, Véronique ; Behn, Mark D.
    Gravity, magnetic, and bathymetry data collected along a continuous 1400-km-long spreading-parallel flow line across the Mid-Atlantic Ridge indicate significant tectonic and magmatic fluctuations in the formation of oceanic crust over a range of timescales. The transect spans from 28 Ma on the African Plate to 74 Ma on the North American plate, crossing the Mid-Atlantic Ridge at 35.8 ºN. Gravity-derived crustal thicknesses vary from 3–9 km with a standard deviation of 1 km. Spectral analysis of bathymetry and residual mantle Bouguer anomaly (RMBA) show diffuse power at >1 Myr and concurrent peaks at 390, 550, and 950 kyr. Large-scale (>10-km) mantle thermal and compositional heterogeneities, variations in upper mantle flow, and detachment faulting likely generate the >1 Myr diffuse power. The 550- and 950-kyr peaks may reflect the presence of magma solitons and/or regularly spaced ~7.7 and 13.3 km short-wavelength mantle compositional heterogeneities. The 390-kyr spectral peak corresponds to the characteristic spacing of faults along the flow line. Fault spacing also varies over longer periods (>10 Myr), which we interpret as reflecting long-lived changes in the fraction of tectonically- vs. magmatically- accommodated extensional strain. A newly discovered off-axis oceanic core complex (Kafka Dome) found at 8 Ma on the African plate further suggests extended time periods of tectonically dominated plate separation. Fault spacing negatively correlates with gravity-derived crustal thickness, supporting a strong link between magma input and fault style at mid-ocean ridges.