RESEARCH TOPICS
RESEARCH TOPICS
Embedded Files
(1) Earthquake Relocation (Click for more details)
Earthquake locations are fundamental for studies of earthquake physics, fault orientations and Earth’s deformation. Accurate earthquake locations are also essential for characterizing magmatic pathways and identifying magma migration in volcanic areas. Improving earthquake location accuracy has been an important and challenging goal in seismology for the past few decades. In our relocation studies, we improve both absolute and relative earthquake location accuracies by applying the three-dimensional ray tracing and differential time relocation methods using waveform cross-correlation data. These approaches have been applied to different tectonically and volcanically active areas, including California, Puerto Rico, and Hawaii.
Earthquake location comparison for Hawaii (Lin et al., 2014).
(2) Seismic Tomography
(a) Velocity Model (Click for more details)
High-resolution three-dimensional (3-D) seismic velocity models are central to seismic and volcanic hazard assessments. 3-D velocity models are necessary for determining accurate earthquake locations and focal mechanisms, developing ground motion models, and relating seismicity to geologic structures. My group mainly applies the local earthquake tomography approaches, such as the simul2000 and double-difference tomography algorithms to invert for models of the compressional-wave velocity (Vp), shear-wave velocity (Vs), and their ratio (Vp/Vs) using seismic observations. We are also involved in ambient noise tomography for crustal and upper mantle velocity structure.
Map view of Vp and Vp/Vs model for Hawaii (Lin et al., 2014).
(b) Attenuation Model (Click for more details)
Seismic attenuation studies provide important independent constraints on Earth properties since their sensitivity to temperature, fluids, compositional differences, and other rock properties is distinct from that provided by P- and S-wave velocities. Tomographic inversions are now commonly applied to determine the three-dimensional attenuation (quantified by 1/Q) structure in a manner comparable to velocity tomography.
Map view of P-wave attenuation model for Hawaii (Lin et al., 2015).
(3) Volcanic Seismology
We apply a high-resolution Vp/Vs ratio estimation method described in Lin and Shearer (2007) using differential times from waveform cross-correlation to study spatial and temporal variations of near-source Vp/Vs ratios in different tectonic regions. The results can help to track movement of magma and volatiles within a volcano and to estimate spatial variations in fracturing and fluid content in active fault zones.
In situ Vp/Vs ratio near Mammoth Mountain (Lin, 2013).
(4) Induced Seismicity
(a) CO2 injection into the underground and storage in the oil and gas reservoir is a practicable and economic way for carbon sequestration. One of the most important geophysical monitoring is to study micro-seismic events induced by the migration and leakage of the injected CO2. We deploy broadband seismometers in Enhanced Oil Recovery (EOR) fields, which can record seismic information in a very wide band of frequency and provide information for the understanding of the characteristics of the induced seismic events.
Long-duration seismic events observed in an EOR field.
(b) Since 2008, the seismicity rate in the state of Oklahoma has significantly increased, which has resulted in speculations about the anthropogenic nature of the observed seismicity. The remarkable spatiotemporal correlation between seismicity (2013-2016) and wastewater injection rates (since 2015) in our study based on earthquake relocation and moment tensor inversion strongly supports the idea that the 2016 Mw 5.8 Pawnee mainshock was induced.
Comparison of the seismicity and daily injection rate in 2015 and 2016 before the Mw 5.8 Pawnee mainshock.
(5) Remote Earthquake Triggering
Earthquake triggering by the seismic waves of large remote earthquakes has been utilized to investigate critically loaded faults. We examine the remote triggering phenomena in geothermal fields and their surrounding areas to assess the anthropogenic effects on the stress state. We find that the geothermal production areas, although with high seismicity rate, are less susceptible to remote triggering, which suggests a less-critical stress state than in the surrounding areas.
Seismicity rate change near the Coso geothermal field after the 1992 Landers earthquake (Zhang et al., 2017).
(6) Subduction Zone Earthquakes (Click here for poster)
We have expanded our local earthquake location methods to the regional and teleseismic events by including more types of phases and other adjustments. For teleseismic studies, we apply these modified methods to relocate intermediate-depth events along 32 slab segments in the Ring of Fire in order to revisit a recent global assessment of Double Seismic Zone (DSZ) layer separations. We reanalyze events from the EHB catalog over a range of age and temperature and find the separation to be highly correlated with subducting slab age, and generally consistent with antigorite dehydration as the mechanism responsible for the intermediate-depth seismicity.
32 slab segments in the Ring of Fire
Seismicity and DSZ layer separation estimation in Honshu, Japan.
Page updated
Google Sites
Report abuse