North Carolina Agricultural and Technical State University (NCA&T) has established a master's deg... more North Carolina Agricultural and Technical State University (NCA&T) has established a master's degree program in Computational Science and Engineering (CSE). The program will be highly interdisciplinary, drawing expertise and resources from various disciplines across the University, and operating outside a department. It will offer an interdisciplinary curriculum combining applied mathematics, high performance parallel and scalable computing, scientific modeling and simulation, data visualization, and domain areas such as physical science and engineering, life sciences, agricultural and environmental sciences, technology and business. The aim of this program is to provide students with an opportunity to (a) master high performance computer programming tools as well as data acquisition and processing techniques; (b) acquire computational modeling, simulation and visualization skills; (c) relate acquired computational science and engineering knowledge and skills to specific application fields of science, engineering, technology and business; and (d) learn to develop novel and robust computational tools and methods to solve scientific, engineering, technological or business problems. Graduates of this program will be highly versatile computational scientists, engineers, technologists or business executives with a good understanding of the connections among various disciplines, and capable of interacting and collaborating effectively with scientists, engineers and other professionals in other fields. The newly established MS degree program in CSE builds upon the University's curricular strength and research capability in science, engineering, mathematics, technology, and business. It is a result of interdisciplinary collaboration among the
We derive a family of sixth-order compact finite-difference schemes for the three-dimensional Poi... more We derive a family of sixth-order compact finite-difference schemes for the three-dimensional Poisson's equation. As opposed to other research regarding higher-order compact difference schemes, our approach includes consideration of the discretization of the source function on a compact finite-difference stencil. The schemes derived approximate the solution to Poisson's equation on a compact stencil, and thus the schemes can be easily implemented and resulting linear systems are solved in a high-performance computing environment. The resulting discretization is a one-parameter family of finite-difference schemes which may be further optimized for accuracy and stability. Computational experiments are implemented which illustrate the theoretically demonstrated truncation errors.
Bulletin of the Seismological Society of America, 2006
Significant surface waves were recorded in the western coastal plain (WCP) of Taiwan during the 1... more Significant surface waves were recorded in the western coastal plain (WCP) of Taiwan during the 1999 Chi-Chi, Taiwan, earthquake and its series of aftershocks. We study in detail the surface waves produced by one aftershock (20 September 1999, 18hr 03m 41.16sec, M 6.2) in this paper. We take the Chelungpu-Chukou fault to be the eastern edge of the WCP because it marks a distinct lateral contrast in seismic wave velocities in the upper few kilometers of the surface. For many records from stations within the WCP, body waves and surface waves separate well in both the time domain and the period domain. Long-period (e.g., Ͼ2 sec) ground motions in the plain are dominated by surface waves. Significant prograde Rayleigh wave particle motions were observed in the WCP. The observed peak ground velocities are about 3-5 times larger than standard predictions in the central and western part of the plain. Observed response spectra at 3 sec, 4 sec, and 5 sec at the center of the plain can be 15 times larger than standard predictions and 10 times larger than the predictions of Joyner (2000) based on surface wave data from the Los Angeles basin. The strong surface waves were probably generated at the boundary of the WCP and then propagated toward the west, largely along radial directions relative to the epicenter. The geometry of the boundary may have had a slight effect on propagation directions of surface waves. Group velocities of fundamental mode Rayleigh and Love waves are estimated using the multiple filter analysis (MFA) technique and are refined with phase matched filtering (PMF). Group velocities of fundamental mode surface waves range from about 0.7 km/sec to 1.5 km/sec for the phases at periods from 3 sec to 10 sec. One important observation from this study is that the strongest surface waves were recorded in the center of the plain. The specific location of the strongest motions depends largely on the period of surface waves rather than on specific site conditions or plain structures. Accordingly, we conjecture that surface waves could be generated in a wide area close to boundaries of low-velocity sedimentary wave guides. In the case studied in this article the area can be as wide as 30 km (from the Chelungpu fault to the center of the plain). Surface waves converted by P and S waves at different locations would overlap each other and add constructively along their propagation paths. As a result, the surface waves would get stronger and stronger. Beyond a certain distance to the boundary, no more surface waves would be generated. Consequently, no more local surface waves would be superimposed into the invasive surface waves, and the surface waves would tend to decay in amplitude with distance.
Bulletin of the Seismological Society of America, 2003
The digital accelerograph network installed in Taiwan produced a rich set of records from the 20 ... more The digital accelerograph network installed in Taiwan produced a rich set of records from the 20 September 1999 Chi-Chi, Taiwan earthquake (M w 7.6). Teledyne Geotech model A-800 and A-900A* digital accelerographs were colocated at 22 stations that recorded this event. Comparisons of the amplitudes, frequency content, and baseline offsets show that records from several of the A-800 accelerographs are considerably different than those from the colocated A-900A accelerographs. On this basis, and in view of the more thorough predeployment testing of the newer A-900A instruments, we recommend that the records from the A-800 instruments be used with caution in analyses of the mainshock and aftershocks. At the Hualien seismic station two A-900A and one A-800 instruments were colocated, along with a Global Positioning System instrument. Although the records from the two A-900A instruments are much more similar than those from a colocated A-800 instrument, both three-component records contain unpredictable baseline offsets, which produced completely unrealistic ground displacements derived from the accelerations by double integration, as do many of the strong-motion data from this event; the details of the baseline offsets differ considerably on the two threecomponent records. There are probably numerous sources of the baseline offsets, including sources external to the instruments, such as tilting or rotation of the ground, and sources internal to the instruments, such as electrical or mechanical hysteresis in the sensors. For the two colocated A-900A records at the Hualien seismic station, however, the differences in the baseline offsets suggest that the principal source is some transient disturbance within the instrument. The baseline offsets generally manifest themselves in the acceleration time series as pulses or steps, either singly or in combination. We find a 0.015-Hz low-cut filter can almost completely eliminate the effects of the baseline offsets, but then information regarding the permanent displacements is lost. The causative mechanisms of the baseline offsets are unknown presently. Hence, it is very difficult to recover the permanent displacements from the modern digital records, although for records close to large earthquakes, the signalto-noise ratio should theoretically be adequate to obtain ground motions with periods of hundreds of seconds. This study reinforces our conclusion from previous studies that the sources of baseline offsets occurring in digital strong-motion records are very complex and often unpredictable, and that, therefore, it is difficult to remove the baseline effects to maximize the information content of the record. The baseline offsets only affect very long period motions (e.g., Ͼ20 sec), however, and therefore are of little or no engineering concern.
Bulletin of the Seismological Society of America, 2006
The U.S. Geological Survey Parkfield Dense Seismograph Array (UP-SAR) recorded successfully stron... more The U.S. Geological Survey Parkfield Dense Seismograph Array (UP-SAR) recorded successfully strong ground motions during the 2004 Parkfield earthquake (M 6.0) and its aftershock series after waiting for 15 years for an anticipated event like this. The array also recorded the 2003 San Simeon earthquake (M 6.5). Because the array covers a very small area (0.45 km 2), these data offer some interesting fresh insights into intrasite variations of seismic ground motions. In this article, we study strong-motion data recorded at the UPSAR from the San Simeon event, the Parkfield event, and its seven aftershocks. We find that the variations of highfrequency ground motions (e.g., Ͼ3 Hz) are very considerable. The largest horizontal peak ground acceleration (PGA) (P11, 408 cm/sec 2) from the Parkfield event is close to three times of the smallest one (P01, 157 cm/sec 2); the largest peak response spectrum is even over three times of the smallest one. The shortest station-to-station distance (between P06 and P07) in the array is only 25 m, but three-component PGAs of the two stations differ from a factor of 1.5 for the Parkfield event. The coefficient of variation (C v ס r/mean) of Fourier acceleration is about 50% at frequencies higher than about 3 Hz. We find that C v depends strongly on frequency, while it is nearly stable for different earthquakes. The significant variation of the high-frequency ground motions seems to be brought about mostly by the local and neighboring topographic effects, which have a larger effect in horizontal than vertical directions. We also calculate the ratio of vertical to horizontal response spectrum. Our plotting shows that the ratio is not sensitive to earthquake magnitude. We compare the observed motions (PGA, 5%-damped pseudoacceleration response spectrum [PSA] from 0.02 to 5 sec) with estimations from four commonly used prediction equations (Abrahamson and Silva, 1997; Boore et al., 1997; Campbell and Bozorgnia, 2003; and Sadigh et al., 1997). The comparisons indicate that the significant station-to-station variation reduces largely the accuracy with which a site-specific estimation can be predicted. However, the mean of the observations at the UPSAR compares reasonably well with these estimations.
The pre-development period of Tropical Storm Debby (2006) initially formed over the Ethiopian Hig... more The pre-development period of Tropical Storm Debby (2006) initially formed over the Ethiopian Highlands (EH) region is studied in conjunction with the African easterly wave (AEW) disturbance and the embedded mesoscale convective systems (MCS). Based on infrared satellite imagery and numerically simulated results, several convective genesis and lysis periods are identified. With the mountains in central and western North Africa replaced by flat terrains, we found that the embedded MCS is weakened and the convective cycles less apparent. Similar effects are found with the reduced moisture content. It is found that the PBL effects and moisture availability are important for maintaining AEW-MCS system as it travels to the west and supporting sufficient moisture by allowing for surface moisture fluxes to affect these systems and aid in convective development. The AEW is slightly modulated by orography downstream from the EH region. Both the EH region and the PBL effects are essential in ...
Bulletin of The Seismological Society of America, 2007
The 2003 San Simeon, California, earthquake (M 6.5) generated a set of colocated and closely spac... more The 2003 San Simeon, California, earthquake (M 6.5) generated a set of colocated and closely spaced high-rate (1-sample-per-second) Global Positioning System (GPS) positions and ground motions from digital accelerographs in the Parkfield region (at epicentral distances of 50 to 70 km). The waveforms of displacements derived from the 13 GPS receivers in the region have dominant periods between about 7 and 18 sec. The waveforms are similar in shape, with a systematic change in waveform as a function of distance from the source. The GPS motions are smaller than the accelerograph motions for periods less than about 2 sec. From this we conclude that the 1-sample-per-sec GPS receivers provide a good representation of ground motion at periods longer than about 2 sec. Perhaps more important for earthquake engineering is that the accelerograph data are similar to the GPS data for periods as long as 30 sec, if not longer. This means that data from digital accelerographs can provide reliable relative-displacement response spectra at the periods needed in the design of large structures, at least for earthquakes with magnitudes of 6.5 or above at distances within 70 km. We combine the colocated or very closely spaced GPS and accelerograph data sets in the frequency domain to obtain a single broadband time series of the ground motion at each accelerograph station. These broadband ground motions may be useful to seismologists in unraveling the dynamic process of fault rupture and to engineers for designing large structures with verylong-period response.
Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Wie... more Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Wien. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to selfarchive your work, please use the accepted author's version for posting to your own website or your institution's repository. You may further deposit the accepted author's version on a funder's repository at a funder's request, provided it is not made publicly available until 12 months after publication.
The formation of African easterly waves (AEWs) and mesoscale convective systems (MCSs) in eastern... more The formation of African easterly waves (AEWs) and mesoscale convective systems (MCSs) in eastern North Africa and its impacts on the tropical cyclogenesis over the eastern Atlantic Ocean is studied. Based on numerical simulations using WRF model, the AEWs during the hurricane season may be generated by the orography and shear zone established by the Somali jet and anticyclonic circulation associated with the Asian monsoon to the north of the Ethiopian Highlands (EH) and Red Sea. The WRF is employed to simulate the pre-hurricane AEW-MCS system of Tropical Storm Debby (2006) near the EH. Finer-resolution numerical simulations demonstrate that the vortex generated on the lee and MCS over the mountain eventually merge and become an AEW-MCS system serving as a precursor of tropical cyclone. The larger-scale environments conducive to the formation of the AEW-MCS system are also investigated.
North Carolina Agricultural and Technical State University (NCA&T) has established a master's deg... more North Carolina Agricultural and Technical State University (NCA&T) has established a master's degree program in Computational Science and Engineering (CSE). The program will be highly interdisciplinary, drawing expertise and resources from various disciplines across the University, and operating outside a department. It will offer an interdisciplinary curriculum combining applied mathematics, high performance parallel and scalable computing, scientific modeling and simulation, data visualization, and domain areas such as physical science and engineering, life sciences, agricultural and environmental sciences, technology and business. The aim of this program is to provide students with an opportunity to (a) master high performance computer programming tools as well as data acquisition and processing techniques; (b) acquire computational modeling, simulation and visualization skills; (c) relate acquired computational science and engineering knowledge and skills to specific application fields of science, engineering, technology and business; and (d) learn to develop novel and robust computational tools and methods to solve scientific, engineering, technological or business problems. Graduates of this program will be highly versatile computational scientists, engineers, technologists or business executives with a good understanding of the connections among various disciplines, and capable of interacting and collaborating effectively with scientists, engineers and other professionals in other fields. The newly established MS degree program in CSE builds upon the University's curricular strength and research capability in science, engineering, mathematics, technology, and business. It is a result of interdisciplinary collaboration among the
We derive a family of sixth-order compact finite-difference schemes for the three-dimensional Poi... more We derive a family of sixth-order compact finite-difference schemes for the three-dimensional Poisson's equation. As opposed to other research regarding higher-order compact difference schemes, our approach includes consideration of the discretization of the source function on a compact finite-difference stencil. The schemes derived approximate the solution to Poisson's equation on a compact stencil, and thus the schemes can be easily implemented and resulting linear systems are solved in a high-performance computing environment. The resulting discretization is a one-parameter family of finite-difference schemes which may be further optimized for accuracy and stability. Computational experiments are implemented which illustrate the theoretically demonstrated truncation errors.
Bulletin of the Seismological Society of America, 2006
Significant surface waves were recorded in the western coastal plain (WCP) of Taiwan during the 1... more Significant surface waves were recorded in the western coastal plain (WCP) of Taiwan during the 1999 Chi-Chi, Taiwan, earthquake and its series of aftershocks. We study in detail the surface waves produced by one aftershock (20 September 1999, 18hr 03m 41.16sec, M 6.2) in this paper. We take the Chelungpu-Chukou fault to be the eastern edge of the WCP because it marks a distinct lateral contrast in seismic wave velocities in the upper few kilometers of the surface. For many records from stations within the WCP, body waves and surface waves separate well in both the time domain and the period domain. Long-period (e.g., Ͼ2 sec) ground motions in the plain are dominated by surface waves. Significant prograde Rayleigh wave particle motions were observed in the WCP. The observed peak ground velocities are about 3-5 times larger than standard predictions in the central and western part of the plain. Observed response spectra at 3 sec, 4 sec, and 5 sec at the center of the plain can be 15 times larger than standard predictions and 10 times larger than the predictions of Joyner (2000) based on surface wave data from the Los Angeles basin. The strong surface waves were probably generated at the boundary of the WCP and then propagated toward the west, largely along radial directions relative to the epicenter. The geometry of the boundary may have had a slight effect on propagation directions of surface waves. Group velocities of fundamental mode Rayleigh and Love waves are estimated using the multiple filter analysis (MFA) technique and are refined with phase matched filtering (PMF). Group velocities of fundamental mode surface waves range from about 0.7 km/sec to 1.5 km/sec for the phases at periods from 3 sec to 10 sec. One important observation from this study is that the strongest surface waves were recorded in the center of the plain. The specific location of the strongest motions depends largely on the period of surface waves rather than on specific site conditions or plain structures. Accordingly, we conjecture that surface waves could be generated in a wide area close to boundaries of low-velocity sedimentary wave guides. In the case studied in this article the area can be as wide as 30 km (from the Chelungpu fault to the center of the plain). Surface waves converted by P and S waves at different locations would overlap each other and add constructively along their propagation paths. As a result, the surface waves would get stronger and stronger. Beyond a certain distance to the boundary, no more surface waves would be generated. Consequently, no more local surface waves would be superimposed into the invasive surface waves, and the surface waves would tend to decay in amplitude with distance.
Bulletin of the Seismological Society of America, 2003
The digital accelerograph network installed in Taiwan produced a rich set of records from the 20 ... more The digital accelerograph network installed in Taiwan produced a rich set of records from the 20 September 1999 Chi-Chi, Taiwan earthquake (M w 7.6). Teledyne Geotech model A-800 and A-900A* digital accelerographs were colocated at 22 stations that recorded this event. Comparisons of the amplitudes, frequency content, and baseline offsets show that records from several of the A-800 accelerographs are considerably different than those from the colocated A-900A accelerographs. On this basis, and in view of the more thorough predeployment testing of the newer A-900A instruments, we recommend that the records from the A-800 instruments be used with caution in analyses of the mainshock and aftershocks. At the Hualien seismic station two A-900A and one A-800 instruments were colocated, along with a Global Positioning System instrument. Although the records from the two A-900A instruments are much more similar than those from a colocated A-800 instrument, both three-component records contain unpredictable baseline offsets, which produced completely unrealistic ground displacements derived from the accelerations by double integration, as do many of the strong-motion data from this event; the details of the baseline offsets differ considerably on the two threecomponent records. There are probably numerous sources of the baseline offsets, including sources external to the instruments, such as tilting or rotation of the ground, and sources internal to the instruments, such as electrical or mechanical hysteresis in the sensors. For the two colocated A-900A records at the Hualien seismic station, however, the differences in the baseline offsets suggest that the principal source is some transient disturbance within the instrument. The baseline offsets generally manifest themselves in the acceleration time series as pulses or steps, either singly or in combination. We find a 0.015-Hz low-cut filter can almost completely eliminate the effects of the baseline offsets, but then information regarding the permanent displacements is lost. The causative mechanisms of the baseline offsets are unknown presently. Hence, it is very difficult to recover the permanent displacements from the modern digital records, although for records close to large earthquakes, the signalto-noise ratio should theoretically be adequate to obtain ground motions with periods of hundreds of seconds. This study reinforces our conclusion from previous studies that the sources of baseline offsets occurring in digital strong-motion records are very complex and often unpredictable, and that, therefore, it is difficult to remove the baseline effects to maximize the information content of the record. The baseline offsets only affect very long period motions (e.g., Ͼ20 sec), however, and therefore are of little or no engineering concern.
Bulletin of the Seismological Society of America, 2006
The U.S. Geological Survey Parkfield Dense Seismograph Array (UP-SAR) recorded successfully stron... more The U.S. Geological Survey Parkfield Dense Seismograph Array (UP-SAR) recorded successfully strong ground motions during the 2004 Parkfield earthquake (M 6.0) and its aftershock series after waiting for 15 years for an anticipated event like this. The array also recorded the 2003 San Simeon earthquake (M 6.5). Because the array covers a very small area (0.45 km 2), these data offer some interesting fresh insights into intrasite variations of seismic ground motions. In this article, we study strong-motion data recorded at the UPSAR from the San Simeon event, the Parkfield event, and its seven aftershocks. We find that the variations of highfrequency ground motions (e.g., Ͼ3 Hz) are very considerable. The largest horizontal peak ground acceleration (PGA) (P11, 408 cm/sec 2) from the Parkfield event is close to three times of the smallest one (P01, 157 cm/sec 2); the largest peak response spectrum is even over three times of the smallest one. The shortest station-to-station distance (between P06 and P07) in the array is only 25 m, but three-component PGAs of the two stations differ from a factor of 1.5 for the Parkfield event. The coefficient of variation (C v ס r/mean) of Fourier acceleration is about 50% at frequencies higher than about 3 Hz. We find that C v depends strongly on frequency, while it is nearly stable for different earthquakes. The significant variation of the high-frequency ground motions seems to be brought about mostly by the local and neighboring topographic effects, which have a larger effect in horizontal than vertical directions. We also calculate the ratio of vertical to horizontal response spectrum. Our plotting shows that the ratio is not sensitive to earthquake magnitude. We compare the observed motions (PGA, 5%-damped pseudoacceleration response spectrum [PSA] from 0.02 to 5 sec) with estimations from four commonly used prediction equations (Abrahamson and Silva, 1997; Boore et al., 1997; Campbell and Bozorgnia, 2003; and Sadigh et al., 1997). The comparisons indicate that the significant station-to-station variation reduces largely the accuracy with which a site-specific estimation can be predicted. However, the mean of the observations at the UPSAR compares reasonably well with these estimations.
The pre-development period of Tropical Storm Debby (2006) initially formed over the Ethiopian Hig... more The pre-development period of Tropical Storm Debby (2006) initially formed over the Ethiopian Highlands (EH) region is studied in conjunction with the African easterly wave (AEW) disturbance and the embedded mesoscale convective systems (MCS). Based on infrared satellite imagery and numerically simulated results, several convective genesis and lysis periods are identified. With the mountains in central and western North Africa replaced by flat terrains, we found that the embedded MCS is weakened and the convective cycles less apparent. Similar effects are found with the reduced moisture content. It is found that the PBL effects and moisture availability are important for maintaining AEW-MCS system as it travels to the west and supporting sufficient moisture by allowing for surface moisture fluxes to affect these systems and aid in convective development. The AEW is slightly modulated by orography downstream from the EH region. Both the EH region and the PBL effects are essential in ...
Bulletin of The Seismological Society of America, 2007
The 2003 San Simeon, California, earthquake (M 6.5) generated a set of colocated and closely spac... more The 2003 San Simeon, California, earthquake (M 6.5) generated a set of colocated and closely spaced high-rate (1-sample-per-second) Global Positioning System (GPS) positions and ground motions from digital accelerographs in the Parkfield region (at epicentral distances of 50 to 70 km). The waveforms of displacements derived from the 13 GPS receivers in the region have dominant periods between about 7 and 18 sec. The waveforms are similar in shape, with a systematic change in waveform as a function of distance from the source. The GPS motions are smaller than the accelerograph motions for periods less than about 2 sec. From this we conclude that the 1-sample-per-sec GPS receivers provide a good representation of ground motion at periods longer than about 2 sec. Perhaps more important for earthquake engineering is that the accelerograph data are similar to the GPS data for periods as long as 30 sec, if not longer. This means that data from digital accelerographs can provide reliable relative-displacement response spectra at the periods needed in the design of large structures, at least for earthquakes with magnitudes of 6.5 or above at distances within 70 km. We combine the colocated or very closely spaced GPS and accelerograph data sets in the frequency domain to obtain a single broadband time series of the ground motion at each accelerograph station. These broadband ground motions may be useful to seismologists in unraveling the dynamic process of fault rupture and to engineers for designing large structures with verylong-period response.
Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Wie... more Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Wien. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to selfarchive your work, please use the accepted author's version for posting to your own website or your institution's repository. You may further deposit the accepted author's version on a funder's repository at a funder's request, provided it is not made publicly available until 12 months after publication.
The formation of African easterly waves (AEWs) and mesoscale convective systems (MCSs) in eastern... more The formation of African easterly waves (AEWs) and mesoscale convective systems (MCSs) in eastern North Africa and its impacts on the tropical cyclogenesis over the eastern Atlantic Ocean is studied. Based on numerical simulations using WRF model, the AEWs during the hurricane season may be generated by the orography and shear zone established by the Somali jet and anticyclonic circulation associated with the Asian monsoon to the north of the Ethiopian Highlands (EH) and Red Sea. The WRF is employed to simulate the pre-hurricane AEW-MCS system of Tropical Storm Debby (2006) near the EH. Finer-resolution numerical simulations demonstrate that the vortex generated on the lee and MCS over the mountain eventually merge and become an AEW-MCS system serving as a precursor of tropical cyclone. The larger-scale environments conducive to the formation of the AEW-MCS system are also investigated.
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