Abstract We present a new three‐dimensional seismic velocity model of the crustal and upper mantle structure for Mauna Loa and Kilauea volcanoes in Hawaii. Our model is derived from the first‐arrival times of the compressional and shear waves from about 53,000 events on and near the Island of Hawaii between 1992 and 2009 recorded by the Hawaiian Volcano Observatory stations. The V p model generally agrees with previous studies, showing high‐velocity anomalies near the calderas and rift zones and low‐velocity anomalies in the fault systems. The most significant difference from previous models is in V p / V s structure. The high‐ V p and high‐ V p / V s anomalies below Mauna Loa caldera are interpreted as mafic magmatic cumulates. The observed low‐ V p and high‐ V p / V s bodies in the Kaoiki seismic zone between 5 and 15 km depth are attributed to the underlying volcaniclastic sediments. The high‐ V p and moderate‐ to low‐ V p / V s anomalies beneath Kilauea caldera can be explained by a combination of different mafic compositions, likely to be olivine‐rich gabbro and dunite. The systematically low‐ V p and low‐ V p / V s bodies in the southeast flank of Kilauea may be caused by the presence of volatiles. Another difference between this study and previous ones is the improved V p model resolution in deeper layers, owing to the inclusion of events with large epicentral distances. The new velocity model is used to relocate the seismicity of Mauna Loa and Kilauea for improved absolute locations and ultimately to develop a high‐precision earthquake catalog using waveform cross‐correlation data.
Abstract A series of conjugate strike‐slip faults is the most prominent geologic feature in central Tibet and is considered to accommodate east‐west extension and coeval north‐south contraction. The development mechanism of the conjugate strike‐slip fault system is under debate because of unclear crustal physical properties and compositional variations. P and S wave arrivals from 414 local earthquakes recorded by the temporary Seismic Array Integrated Detection for a Window of Indian Continental Head array and the permanent China National Seismic Network were used for the velocity tomography, with additional P and S wave arrivals from 12 shots of the International Deep Profiling of Tibet and the Himalaya III reflection/refraction profile. The local earthquakes were simultaneously relocated with the updated velocity models. We also inverted for a three‐dimensional upper crustal Qp model with the same earthquake data set. The Vp structure near the surface shows that low‐Vp anomalies generally correspond to sedimentary basins and high‐Vp anomalies are related to exhumed metamorphic blocks in the study area. Relatively low Vp/Vs ratios in the upper crust indicate widely distributed quartz‐rich rocks. The low‐Vp zone from 0‐ to 10‐km depth (resolving depth limit) is spatially correlated with the Bangong‐Nujiang suture, possibly reflecting the compositional difference along the ophiolitic mélange belt accompanied by twin volcanic arcs from a double‐sided subduction. This interpretation is supported by relatively heterogeneous Qp values. This low‐velocity zone also implies relatively uniform stress and continuous deformation in the upper crust of central Tibet. The relatively weak materials in at least the upper crust would result in strain concentration and help the development of the conjugate strike‐slip fault system along the Bangong‐Nujiang suture.
Author(s): Lin, Guoqing | Abstract: Earthquake locations are fundamental to studies of earthquake physics, fault orientations and Earth's deformation. Improving earthquake location accuracy has been an important goal branch in seismology for the past few decades. In this dissertation, I consider several methods to improve both relative and absolute earthquake locations. Chapter 2 is devoted to the comparison of different relative earthquake location techniques based on synthetic data, including the double-difference and source -specific station term (SSST) method. The shrinking box SSST algorithm not only provides similar improvements in relative earthquake locations compared to other techniques, but also improves absolute location accuracy compared to the simple SSST method. Chapter 4 describes and documents the COMPLOC software package for implementing the shrinking box SSST algorithm. Chapter 3 shows how absolute locations for quarry seismicity can be obtained by using remote sensing data, which is useful in providing absolute reference locations for three-dimensional velocity inversions and to constrain the shallow crustal structure in simultaneous earthquake location and velocity inversions. Chapter 5 presents and tests a to estimate local Vp/Vs ratios for compact similar earthquake clusters using the precise P- and S- differential times obtained using waveform cross-correlation. Chapter 6 describes a new three-dimensional seismic velocity model for southern California obtained using the composite event method applied to the SIMULPS tomographic inversion algorithm. Based on this velocity model and waveform cross-correlation, Chapter 7 describes how a new earthquake location catalog is obtained for about 450,000 southern California earthquakes between 1981 and 2005
We develop and test a method to estimate local Vp / Vs ratios for compact similar earthquake clusters using the precise P and S differential times obtained using waveform cross-correlation. We demonstrate how our technique works using synthetic data and evaluate likely errors arising from near-source takeoff angle differences between P and S waves. We use a robust misfit function method to compute Vp / Vs ratios for both synthetic data sets and several similar event clusters in southern California, and use a bootstrap resampling approach to estimate standard errors for real data. Our technique has higher resolution for near-source Vp / Vs ratios than typical tomographic inversion methods and provides constraints on near-fault rock properties.
Nicastrin (NCT) is an essential component of gamma-secretase, a multiprotein complex that catalyzes intramembranous cleavage of APP, Notch and other substrates. Shah, Yu and colleagues have reported that the large ectodomain of NCT functions as a receptor that recognizes and captures substrate to facilitate proteolysis. At present, very little information has emerged pertaining to the domains through which the components within the complex interact, or the structural basis for NCT recognition and binding to substrates. We have employed a co-crystallization strategy that provides a superb methodology to facilitate crystal growth and improve crystal quality for nicastrin structural studies. We purified nicastrin ectodomain (NCTect) from the medium of a mammalian cell line that stably expresses NCTect, and deglycosylated this subject to remove N-glycans. Using a phage library that displays a large number of potential binders with desired diversities, we performed multiple rounds of affinity selection against NCTect. Eight independent Fab fragments have been successfully identified that tightly bind NCTect. The binding strength was determined by surface plasmon resonance biosensor, with dissociation constants in the lower nanomolar range. The nicastrin and Fab fragment form stable complexes which are now being isolated and purified for crystallization trials.
SUMMARY In the Gulf of California, Mexico, the relative motion across the North America–Pacific boundary is accommodated by a series of marine transform faults and spreading centres. About 40 M> 6 earthquakes have occurred in the region since 1960. On 2009 August 3, an Mw 6.9 earthquake occurred near Canal de Ballenas in the region. The earthquake was a strike-slip event with a shallow hypocentre that is likely close to the seafloor. In contrast to an adjacent M7 earthquake, this earthquake triggered a ground-motion-based earthquake early warning algorithm being tested in southern California (∼600 km away). This observation suggests that the abnormally large ground motions and dynamic strains observed for this earthquake relate to its rupture properties. To investigate this possibility, we image the rupture process and resolve the slip distribution of the event using a P-wave backprojection approach and a teleseismic, finite-fault inversion method. Results from these two independent analyses indicate a relatively simple, unilateral rupture propagation directed along-strike in the northward direction. However, the average rupture speed is estimated around 4 km s−1, suggesting a possible supershear rupture. The supershear speed is also supported by a Rayleigh wave Mach cone analysis, although uncertainties in local velocity structure preclude a definitive conclusion. The Canal de Ballenas earthquake dynamically triggered seismicity at multiple sites in California, with triggering response characteristics varying from location-to-location. For instance, some of the triggered earthquakes in California occurred up to 24 hr later, suggesting that nonlinear triggering mechanisms likely have modulated their occurrence.
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