Yong LiAssociate Professor (Research) of Earth Sciences
Phone: (213) 740-3556
Office: ZHS B11
- Ph.D. Geophysics (Seismology), University of Southern California, 1987
Academic Appointment, Affiliation, and Employment History
Non-Tenure Track Appointments
- Research Professor, Earth Sciences, 2012-2013
- Research Professor, Earth Sciences, 2010-2011
Visiting and Temporary Appointments
- Visiting Professor, Fudan University, 2009-2010
- Honorary Professor, China Academy of Geological Science, 2012-2013
Description of Research
(1) Characterization of earthquake faults includes the pioneering work in discovery and simulation of the fault-zone trapped waves, high-resolution delineation of internal structure and physical properties in 3-D, fault rock co-seismic damage and post-mainshock heal at major active faults in California, Japan, China and New Zealand. (2) Investigation of crustal fracturing and anisotropy in active tectonic margins from shear-wave splitting observations and computation. Developed 2-D and 3-D dynamic ray tracing for seismic waves propagating in the crustal cracked media for evaluation of the in-situ stress states associated with occurrence of earthquakes. (3) Investigation of the crustal structure and evolution by seismic reflection/refraction profiling at Western U.S (COCOOP). Developed a combination computer modeling procedure of multi-channel reflection/refraction profiles, ray tracing, gravity and plate flexure to interpret the seismotectonic structures. (4) Analysis of earthquake source parameters using the method of joint inverse of source and path effects, and the Empirical Green's Function (EGF) method to study the dependence of corner frequency with depth and the stress drop with seismic moment. (5) High-resolution image using fault-zone guided waves for the subsurface water-born fracture zone in geothermal areas and 3-D tomography migration to image the shape of geothermal reservoir, aiming at the development of sustainable renewal energy from deep geothermal resources in the world.
Detailed Statement of Research Interests
I. Seismic Documentation of Subsurface Damage Zones of the M7.2 Darfield and M6.3 Christchurch Earthquake Sequence in New Zealand Using Fault-Zone Trapped Waves: The M6.3 Christchurch earthquake struck the Canterbury region in NZ's South Island on 22 February 2011, following ~6 months after the 2010 M7.1 Darfield earthquake in the same region. In order to document the subsurface structure of the damage zones caused by multiple slips in this earthquake sequence, we deployed two short linear seismic arrays at Canterbury rupture zones to record aftershocks in 2011. We have examined waveform data recorded for 853 aftershocks and identified prominent fault-zone trapped waves (FZTWs) with large amplitude and long wavetrains at stations of Array 1 located within the Darfield surface rupture zone for aftershocks occurring along the Greendale fault (GF) and the Port Hills fault (PHF), which ruptured in the 2010-2011 Canterbury earthquake sequence. The post-S durations of these FZTWs increase as event depths and epicentral distances increase, showing an effective low-velocity waveguide formed by severely damaged rocks extending along the GF and PHF at seismogenic depth. The FZTWs suggest that the Darfield rupture zone extends eastward as bifurcating blind fault segments an additional ~5-8 km beyond the mapped ~30-km extent of the GF surface rupture, consistent with aftershock distributions and geodetic models. On the other hand, the main rupture of the Mw6.3 Christchurch earthquake is ~15-km in length on the blind PHF dipping to SSE, but it likely extends westward along the aftershock lineament approaching the east blind extension of the Darfield/GF rupture. There exists a moderate portion of the low-velocity waveguide at depth in the step-over zone between the GF and PHF, where rocks might have experienced mild damage during the Darfield and Christchurch earthquakes and by 11 M=5 aftershocks occurring in this zone. The rupture segment of their largest M6 aftershock runs along an eastern blind branch of the PHF. Extensive observations and preliminary simulations of these FZTWs show that the main rupture zone on the GF and PHF is ~200-250-m wide in which velocities are reduced by 35-55% with the maximum reduction in the ~75-m-wide damage core zone. The damage zone on the GF extends down to the depth of 8-10 km or deeper. Our study also illuminates a potential approach to investigate the blind rupture zone in urban areas where the deployment of a seismic array is difficult, using FZTWs recorded at the array deployed at its surface section in suburban area. II. Collaborative Research: High-Resolution Imaging of on- and off-Fault Rock Damage at Parkfield, CA, Using P- and S-type Fault-Zone Trapped Waves and F3DT Tomography: The P-type FZTWs recorded at the SAFOD main-hole (MH) seismograph help to improve the image of the heart part of fault-zone damage with high-resolution. The F3DT method allows us to achieve the velocity attenuation structure in 3-D more objectively and with less uncertainty. The present proposal aims to obtain an entire 3-D picture of the fault damage structure and its variations (in fault-zone geometry, velocity, attenuation, rock damage magnitude and depth extent) along the fault strike in Parkfield region, using all the information required for conducting the full-3D waveform tomography (F3DT). III. Collaborative Research with USC, UOW: 3-D Image of Rock Damage of the Calico Fault and Its Heterogeneity Using F3DT for Fault-Zone Trapped Waves: We shall examine the more detailed heterogeneity in magnitude of rock damage along the Calico fault and particularly the damage extent at depth using the F3DT method . In the F3DT algorithm, both the reference structural model and the derived model perturbations are all 3D in space. The full wave sensitivity (Fréchet) kernels are calculated from the full physics of 3D wave propagation, which is implemented using the finite-difference method. In the proposed study, we shall apply the time-lapse, joint inversions for both seismic velocity and attenuation structures of the CF using waveforms recorded for explosions and earthquakes in the previous experiment. We’ll also identify the fault-zone trapped waves from telemetric earthquakes and use them to document the depth extent of the low-velocity compliant zone of the CF. IV. Collaborative research project on “Long-Term Borehole Geophysical Observations in the 5.2-km-Deep Scientific Drilling Well of Chinese Academy of Geological Science(CAGS)in China” using Borehole Instruments Made by Institution of Earth Science and Engineering (IESE) at University of Auckland (UOA) in New Zealand. V. Investigation of the Rock Damage and Heal on the Longmen-Shan Fault Ruptured in the 2008 M8 Wenchuan Earthquake in China: Results from the FZTWs show a distinct low-velocity zone (LVZ) composed by severely damaged rocks at seismogenic depths. Through numerical investigations of trapping efficiency for a dip fault, we imaged a damaged zone several hundred meters wide along the thrusting LSF, within which seismic velocities are reduced by ~30-60% from wall-rock velocities with the maximum velocity reduction in the fault core at shallow depth. We interpret this remarkable LVZ as being a break-down zone accumulating damages caused by dynamic rupture in historical major earthquakes, mainly in the 2008 M8 earthquake, which eventually forms a distinct low-velocity waveguide to trap seismic waves. Because the amplitude and dispersion feature of FZTWs are sensitive to the source location with respect to the waveguide, these waves allow us to delineate the geometry of fault-zone damage along with the principal slip of the Wenchuan mainshock at seismogenic depth based on locations of those aftershocks generating prominent FZTWS. By examining the changes in the dispersion features of FZTWS recorded at the same station for similar earthquakes occurring before and after the 2008 Wenchuan earthquake, we estimate that seismic velocities within the LVZ along the south LSF was reduced by ~10% likely due to the co-seismic damage of fault rocks (with rigidity weakening) during the 2008 M8 mainshock. This value is larger than the damage magnitude of fault rocks caused by the 1992 M7.4 Landers, 1999 M7.1 Hector Mine and 2004 M6 Parkfield earthquakes in California, probably due to the different sizes of slip and stress drop, and faulting mechanisms in these earthquakes. VI. Investigate Geothermal Renewal Energy: Promoting the project of the geothermal power project for China-US Collaborative Agreement in Environment and Energy.
- Li, Y. (2012). Imaging, Modeling and Assimilation in Seismology. (Vol. V1). Beijing in China and Boston in US: China High Education Press and De Gruyter.
- Li, Y. (2012). Fault-Zone Trapped Waves: High-Resolution Characterization of the Damage Zone of the Parkfield San Andreas Fault at Depth. Imaging, Modeling and Assimilation in Seismology (Vol. V1). pp. 107-150. Beijing in China and Boston in US: China High-Education Press with De Gruyter.
- Li, Y. (2012). Fault-zone trapped waves at a dip fault: Documentation of rock damage on the thrusting Longmen-Shan fault ruptured in the 2008 M8 Wenchuan earthquake. Imaging, Modeling and Assimilation in Seismology (Vol. V1). pp. 151 - 198. Beijing in China and Boston in US: China High Education Press and De Gruyter.
- Duan, B. (2011). Deformation of compliant fault zones induced by nearby earthquakes: Theoretical investigations in two dimensions. Journal of Geophysics Research. Vol. B3 (116), pp. 12.
- Li, Y. (2010). Fault Damage in the 2008 M8 Wenchuan Earthquake Epicentral Region. Academic Prospective. Vol. V6 (No. 1), pp. 2-16.
- Li, Y. (2009). High-resolution imaging of the San Andreas Fault damage zone from SAFOD main-hole and surface seismic records. PAGEOPH. Vol. Special/ISESEP
- Cochran, E. E., Li, Y., Shearer, P., Vidale, J. (2009). Seismic and geodetic evidence for extensive, long-lived fault. Geology. Vol. v37 No. 4 (doi: 10.1130/G25306A), pp. 315–318.
- Li, Y. G. (2008). San Andreas Fault damage at SAFOD viewed with fault-guided waves. Geophysical Research Letter. Vol. 35 (L08304/doi:10.1029/2007GL032924), pp. 6.
- Li, Y. (2008). Seismic Study of the San Andreas Fault in California and the Longmen-Shan Fault Ruptured in the 2008 M8 Wenchuan Earthquake in China. Academic Prospective/CSASC. Vol. 4, pp. 155-167.
- Li, Y. (2007). Parkfield fault-zone guided waves: Low-velocity damage zone on the San Andreas fault at depth near SAFOD site at Parkfield by fault-zone trapped waves. Scientific Drilling/IODP. Vol. Sepetember, , Special Issue No. 1 (doi:10.2204/iodp.sd.s01.09.2007), pp. 73-77.
- Li, Y. G. (2007). Seismic Velocity Variations on the San Andreas Fault Caused by the 2004 M6 Parkfield Earthquake and Their Implications. Earth, Planets and Space/TERRAPUB. Vol. 59, pp. 21-31.
- Li, Y. G. (2007). Low-velocity damage zone on the San Andreas fault at depth near SAFOD site at Parkfield by fault-zone trapped waves. Scientific Drilling. (Special Issue, No. 1), pp. 73-77.
- Li, Y. G. (2006). Seismic evidence for rock damage and healing on the San Andreas fault associated with the 2004 M6 Parkfield earthquake, Special issue for Parkfield M6 earthquake. Bulletin of Geological Society of America. Vol. 96 (No.4), pp. S1-15, doi:10.1785/0120050803.
- Cochran, E. S., Li, Y. G. (2006). Anisotropy in the shallow crust observed around the San Andreas fault before and after the 2004 M6 Parkfield earthquake. Bull. Seism. Soc. Am.. Vol. 96, pp. 364-375.
- Li, Y. G. (2004). Low-velocity damaged structure of the San Andreas fault at Parkfield from fault-zone trapped waves. Geophysical Research Letters/American Geophysical Union. Vol. V31, pp. 1-5, L12S06.
- Oglesby, D. D., Day, S. M., Li, Y. G. (2003). The 1999 Hector Mine earthquake: The dynamics of a branched fault system. Bull. Seism. Soc. Am.. Vol. 93, pp. 2459-2476.
- Li, Y. G. (2003). Characterization of rupture zones at Landers and Hector Mine, California in 4-D by fault-zone guided waves. Earth Sci. Frontiers. Vol. V10 (No. 4), pp. 479-505.
- Cochran, E. S., Vidale, J. E., Li, Y. G. (2003). Near-fault anisotropy following the Hector Mine earthquake. J. Geophys. Res.. Vol. 108 (B9), pp. 2436-2447.
- Li, Y. G. (2003). Post-seismic fault healing on the 1999 M7.1 Hector Mine, California earthquake. Bull. Seism. Soc. Am.. Vol. 93 (No. 2), pp. 853-864.
- Li, Y. G. (2003). Multiple-fault rupture of the M7.1 Hector Mine, California, earthquake from fault-zone trapped waves. J. Geophys. Res.. Vol. 108 (ESE 11, 1-25)
- Li, Y. G. (2003). Damage to the shallow Landers fault from the nearby Hector Mine earthquake. Nature. Vol. V421, pp. 524-526.
- Li, Y. G. (2002). Study of the M7.1 Hector Mine, California, earthquake fault plan by fault-zone trapped waves. Bull. Seism. Soc. Am.,. Vol. 92, pp. 1318-1332.
- Li, Y. G. (2001). Shallow seismic profiling at the Punchbowl fault zone, southern California. Shallow seismic profiling at the Punchbowl fault zone, southern California. Vol. 91, pp. 1820-1830.
- Li, Y. G. (2001). Characterization of the San Jacinto fault zone near Anza, California, by fault-zone trapped waves. J. Geophys. Res.. Vol. 106, pp. 30676-30688.
- Li, Y. G. (2001). Healing of the shallow fault zone from 1994-1998 after the 1992 M7.5 Landers, California, earthquake. Geophy. Res. Lett.. Vol. 28 (No.15), pp. 2999-3002.
- Li, Y. G. (2000). Depth-dependent structure of the Landers fault zone from trapped waves generated by aftershocks. J. Geophys. Res.. Vol. 105, pp. 6237-6254.
- Li, Y. G. (1999). Shallow structure of the Landers fault zone using explosion-excited trapped waves. J. Geophys. Res.. Vol. 104, pp. 20,257-20,275.
- Li, Y., Aki, K. (1998). A delineation of the Nojima fault ruptured in the M7.2 Kobe, Japan, earthquake of 1995 using fault zone trapped waves. J. Geophys. Res.. Vol. 103 (B4), pp. 7247-7263.
- Li, Y. G. (1998). Evidence of shallow fault zone strengthening after the 1992 M7.5 Landers, California, earthquake. Science. Vol. V279, pp. 217-219.
- Li, Y., Vernon, F. (1997). San Jacinto fault zone guided waves: A discrimination for recently active fault strands near Anza, California. J. Geophys. Res.. Vol. 102 (B6), pp. 11,689-11,701.
- Li, Y., Ellsworth, W., Thurber, C. (1997). Observations of fault-zone trapped waves excited by explosions at the San Andreas fault, central California. Bull. Seism. Soc. Am.. Vol. 87 (No. 1), pp. 210-221.
- Li, Y. (1996). Shear-wave splitting observations in the Los Angeles basin, California: Implications on stress regimes and crustal fracturing. J. Geophys. Res.. Vol. 101 (B6), pp. 13947-13961.
- Li, Y., Vidale, J. E. (1996). Low-velocity fault zone guided waves; numerical investigations of trapping efficiency. Bull. Seism. Soc. Am.. Vol. V86 (No. 2), pp. 371-378.
- Li, Y. G. (1994). Fine structure of the Landers fault zone; segmentation and the rupture process. Science. Vol. 256, pp. 367-370.
- Li, Y., Aki, K. (1994). Seismic guided waves trapped in the fault zone of the Landers, California, earthquake of 1992. J. Geophys. Res.. Vol. V99 (No. 6), pp. 11,705¬11,722.
- Li, Y. (1994). Shear-wave splitting observations in the northern Los Angeles basin, California. Bull. Seism. Soc. Am.. Vol. V84 (No. 2), pp. 307-323.
- Li, Y., Henyey, T., Lee, S. (1992). Aspect of crustal tectonics in the Western Mojave Desert, California, from seismic, gravity and magnetic profiling. J. Geophys. Res.. Vol. V97 (No. 6), pp. 8805-8816.
- Li, Y., Henyey, T., Leary, P. (1992). Seismic reflection constraints on the structure of the crust beneath the San Bernardino Mountains, Transverse Ranges, southern California. J. Geophys. Res.. Vol. V97 (No. 6), pp. 8817-8830.
- Li, Y., Leary, P. (1990). Fault zone trapped seismic waves. Bull. Seism. Soc. Am.. Vol. V80 (No. 5), pp. 1245-1271.
- Li, Y. G. (1990). Seismic trapped modes in the Oroville and San Andreas fault zones. Science. Vol. V249, pp. 763-766.
- Li, Y., Leary, P., Aki, K. (1990). Ray series modeling of seismic wave traveltime and amplitude in three-dimensional heterogeneous anisotropic crystalline rock: Borehole VSP seismograms from Mojave Desert, California. J. Geophys. Res.. Vol. V95 (No. 7), pp. 11,105-11,358.
- Li, Y., Leary, P., Henyey, T. (1988). Stress orientation inferred from shear wave splitting in basement rock at Cajon Pass. Geophys. Res. Letters. Vol. v15 (No. 9), pp. 997-1,000.
- Li, Y., Leary, P., Aki, K. (1987). Observation and modeling of fault zone fracture seismic anisotropy -. Geophys. J. R. astr. Soc, V91, No. , pp. 461-492, 1987. Vol. v91, pp. 461-492.
Service to the University
Other Service to the University
- An Ambassador for USC to promote the international high education between US and China. , 2012-2013
Service to the Profession
- AGU, SSA, SEG, 2012-2013
- Zumberge Hall of Science (ZHS)
- Los Angeles, CA 90089-0740
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