Department of Geoscience, Stony Brook University
Faculty / Staff / Department of Geosciences / Stony Brook University
Lianxing Wen
Professor

Office: ESS 230
Department of Geosciences
State University of New York at Stony Brook
Stony Brook, NY, 11794
Phone: (631) 632-1726; Fax: (631) 632-8240
E-mail Address: Lianxing.Wen at stonybrook.edu
Ph.D., California Institute of Technology, 1998
Faculty member at Stony Brook since 2000



Professor Wen is a theoretical and observational seismologist and geodynamicist. His research is directed toward understanding the structure, dynamics, composition and evolution of the Earth and other planets. He uses seismic waves to probe the internal structure of the Earth and its change with time, combines seismic and mineral physics data to constrain the composition of the mantle, and develops geodynamical models of how Earth's internal processes govern the Earth's continental drift, surface uplift, surface large igneous province, geochemistry, intra-plate deformation and volcanism. He also has a strong interest in developing new techniques for simulating viscous flow and seismic wave propagation.



Discoveries of Earth's Interior

Professor Wen's group has made many seminal discoveries of the Earth's interior that have fundamentally changed the views of how the Earth works. Among those discoveries are: the east-west hemispheric difference of seismic velocity and attenuation in the top of the inner core, localized temporal change of inner core surface, inner core surface topography and localized mushy zone in the top of the inner core, two continental-scale compositional anomalies at the base of the mantle beneath Africa and Pacific, and various ultra-low velocity zones beneath many hotspots.

Nuclear Test Monitoring

Professor Wen's group's has developed seismic methods for studying nuclear tests and applied them to the monitoring of North Korea's nuclear tests. His group was the first to adopt a relative relocation method to determine the location of a nuclear test reaching a resolution of in the order of 100 meters, and was the first to pinpoint North Korea's 2009 nuclear test beneath Mount Mantap.

Mantle Geodynamics and Geochemistry

Professor Wen's group's research in mantle geodynamics and geochemistry is directed at exploring the physical process that relates the geodynamical observables (geoid, topography, plate motions and intra-plate stresses) and geochemical anomalies (such as the DUPAL anomaly) observed at the surface to the seismic anomalies in the Earth's interior.

Deep Earthquakes

Professor Wen's group's research has systematically studied the source processes of global large deep-focus (depth >400 km) earthquakes with Mw > 7.0 from 1994 to 2012. The earthquakes are classified into three categories: 1) category one, with non- planar distribution and variable focal mechanisms of sub-events, represented by the 1994 Mw 8.2 Bolivia earthquake and the 2013 Mw 8.3 Okhotsk earthquake; 2) category two, with planar distribution but focal mechanisms inconsistent with the plane; and 3) category three, with planar distribution and focal mechanisms consistent with the plane. We suggest that the inferred source processes of large deep-focus earthquakes can be best interpreted by cascading failure of shear thermal instabilities in pre-existing weak zones, with the perturbation of stress generated by a shear instability triggering another and focal mechanisms of the sub-events controlled by orientations of the pre-existing weak zones.

Microseismic Source

We find that microseisms generated by Hurricane Sandy exhibit coherent energy within 1 h time windows in the frequency band of 0.1–0.25 Hz, but with signals correlated among seismic stations aligned along close azimuths from the hurricane center. With the identification of this signal property, we show that travel time difference can be measured between the correlated stations. These correlated seismic signals can be attributed to two types of seismic sources, with one group of the seismic signals from the hurricane center and the other from coastal region. The seismic sources in coastal region are diffusive and move northward along the coastline as Sandy moves northward. We further develop a hurricane seismic source model, to quantitatively describe the coupling among sea level pressure fluctuations, ocean waves, and solid Earth in the region of hurricane center and determine the evolution of source’s strength and pressure fluctuation in the region of hurricane center using seismic data. Strong seismic sources are also identified near the coastal region in New England after Sandy’s dissipation, possibly related to subsequent storm surge in the area. The seismic method may be implemented as another practical means for hurricane monitoring, and seismological estimates of the hurricane seismic source model could be used as in situ proxy measurements of pressure fluctuation in the region of hurricane center for hurricane physics studies.

Induced Seismicity

Hutubi gas field, the largest gas storage field in China, has been operated on annual injection/extraction cycles since 9 June 2013. We study the seismicity near the gas field from 9 June 2013 to 22 October 2015, a time span that the gas field has experienced three injection periods and two extraction periods, and explore its physical mechanism based on the relationship between seismicity and field operation. We identify 273 events (ML > 1) in the region within 10 km of the gas field, with 97% of those occurring in the first two injection periods, 0.4% in the third injection period, and 1% in the two extraction periods. Seismicity in the first two injection periods occurs mostly as shallow clusters (focal depth < 2 km) at two locations: with one along the fault that marks the southern boundary of the gas field and the other about 2 km south to the southeastern tip of the gas field with the seismicity distributed along north‐south direction. The seismicity does not correlate with total gas injection volume, injection rate, or well pressure. It instead occurs 11–17 hr after simultaneous abrupt increases/decreases of gas injection rate and well pressure in the field operation in the first two injection periods when some accumulative injection has reached. Such relationship is consistent with a physical mechanism that the seismicity near Hutubi gas field is induced on pore‐pressured faults with a rate‐ and state‐dependent friction law through an abrupt change of stress in elastic and undrained poroelastic responses to simultaneous abrupt changes of injection rate and well pressure. Our study also points to the possibility that induced seismicity may be controllable in some practical field operations.

Hydrology and Near-surface Geodynamics

We establish a physical framework and build a preliminary database of stress changes on the Earth from 2000 to 2017 in a global scale and at various depths. We consider six loading forces that would generate stress changes on the Earth: hydrological loading, atmospheric pressure, ocean water (including tides and nontidal variation), solid lunisolar tides, pole tide, and postglacial rebound (PGR). The maximum amplitudes of normal deviatoric stress changes on the Earth's surface caused by hydrological loading, atmospheric pressure, and solid lunisolar tides reach 10−2 bar, those by pole tide 10−4–10−3 bar, and those by ocean tides 10−1 bar mostly in the coastal regions. The shear stress changes are about 1 order of magnitude smaller than the normal deviatoric stresses. The PGR‐induced stress rates are 10−3–10−2 bar/year. Stress variations caused by the different forces also exhibit different spatial patterns, with large hydro‐induced stresses mainly distributed in torrid and frigid zones, atmosphere‐induced stresses in temperate and frigid zones, and ocean‐induced stresses in coastlands and PGR‐induced stress rates in Greenland, north Europe, North America, and Antarctica. The hydro‐induced stresses exhibit significant seasonal variations in Amazon Basin, northern India, and central Africa and persistent increase/decrease in Antarctica, Greenland, and Alaska due to ice shelf melting. All loading‐induced stress changes exhibit significant depth variations. The stress database would provide a resource for better understanding the triggering mechanisms of various tectonic events, and the physical framework we establish to build the database could be useful for better studying properties and physical states of Earth's interior.`

Mars' Composition and Dynamics

We use the total mass, possible core radius and the observed mean moment of inertia factor of Mars to constrain mineralogical and compositional structures of Mars. We adopt a liquid Fe–S system for the Martian core and construct density models of the interior of Mars for a series of mantle compositions, core compositions and temperature profiles. The moment of inertia factor of the planet is then calculated and compared to the observation to place constraints on Mars composition. Based on the independent constraints of total mass, possible core radius of 1630–1830 km, and the mean moment of inertia factor ð0:3645 􏰀 0:0005Þ of Mars, we find that Fe content in the Martian mantle is between 9.9 and 11.9 mol%, Al content in the Martian mantle smaller than 1.5 mol%, S content in the Martian core between 10.6 and 14.9 wt%. The inferred Fe content in the bulk Mars lies between 27.3 and 32.0 wt%, and the inferred Fe/Si ratio in Mars between 1.55 and 1.95, within a range too broad to make a conclusion whether Mars has the same nonvolatile bulk composition as that of CI chondrite. We also conclude that no perovskite layer exists in the bottom of the Martian mantle. Based on the inferred density models, we estimate the flattening factor and J2 gravitational potential related to the hydrostatic figure of the rotating Mars to be ð5:0304 􏰀 0:0098Þ 􏰁 10􏰂3 and ð1:8151 􏰀 0:0065Þ 􏰁 10􏰂3 , respectively. We also discuss implications of these compositional models to the understanding of formation and evolution of the planet

Method Developments

Professor Wen's group also developed hybrid methods and migration methods. Hybrid methods are combinations of analytical and numerical methods, with numerical methods applied in heterogeneous regions only and analytical methods outside.




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