In this study, records from a 3-yr intensified observational experiment at eight stations along the hillside of Seqilashan over the southeastern Tibetan Plateau were analyzed and combined with records at 28 routine ob...In this study, records from a 3-yr intensified observational experiment at eight stations along the hillside of Seqilashan over the southeastern Tibetan Plateau were analyzed and combined with records at 28 routine observation stations in the Chinese National Meteorological Station Network to investigate the influences of station location on the different diurnal rainfall variations between station records and Tropical Rainfall Measuring Mission （TRMM） data products. The results indicate that the diurnal variation of warm season rainfall is closely related to location of stations. The prevailing nocturnal rainfall peak in observations at routine stations can be largely attributed to the relatively lower location of the stations, which are mostly situated in valleys. The records at Seqilashan stations on hillsides revealed an evident diurnal afternoon peak of warm season rainfall, similar to that indicated by TRMM data. The different diurnal phases between valley and hillside stations are closely related to the orographically induced regional circulations caused by the complex topography over the Tibetan Plateau. The results of this study indicate that the prevailing nocturnal rainfall associated with the relatively lower location of routine observation stations can partially explain the diurnal rainfall variations between observation station records and TRMM data.展开更多
An advanced earthquake location technique presented by Prugger and Gendzwill (1988) was introduced in this paper. Its characteristics are: 1) adopting the difference between the mean value by observed arrival times an...An advanced earthquake location technique presented by Prugger and Gendzwill (1988) was introduced in this paper. Its characteristics are: 1) adopting the difference between the mean value by observed arrival times and the mean value by calculated travel times as the original reference time of event to calculate the traveltime residuals, thus resulting in the 'true' minimum of travel-time residuals; 2) choosing the L1 norm statistic of the residuals that is more suitable to earthquake location; 3) using a simplex optimized algorithm to search for the minimum residual value directly and iteratively, thus it does not require derivative calculations and avoids matrix inversions, it can be used for any velocity structures and different network systems and can solve out hypocentral parameters (λ, ,h) rapidly and exactly; 4) original time is further derived alone, so the trade-off between focal depth and original time is avoided. All these prominent features make us obtain more accurate Tibetan earthquake locations in the rare network condition by using this method. In this paper, we examined these schemes for our mobile and permanent networks in Tibet with artificial data sets,then using these methods, we determined the hypocentral parameters of partial events observed in the field work period of this project from July 1991 to September 1991 and the seven problematic earthquakes during 1989 - 1990. The hypocentral location errors may be estimated to be less than 3. 6 km approximately. The events with focal depth more than 40 km seem to be distributed in parallel to Qinghai-Sichuan-Yunnan arc structural zone.展开更多
With dense seismic arrays and advanced imaging methods, regional three-dimensional （3D） Earth models have become more accurate. It is now increasingly feasible and advantageous to use a 3D Earth model to better loca...With dense seismic arrays and advanced imaging methods, regional three-dimensional （3D） Earth models have become more accurate. It is now increasingly feasible and advantageous to use a 3D Earth model to better locate earthquakes and invert their source mechanisms by fitting synthetics to observed waveforms. In this study, we develop an approach to determine both the earthquake location and source mechanism from waveform information. The observed waveforms are filtered in different frequency bands and separated into windows for the individual phases. Instead of picking the arrival times, the traveltime differences are measured by cross-correlation between synthetic waveforms based on the 3D Earth model and observed waveforms. The earthquake location is determined by minimizing the cross-correlation traveltime differences. We then fix the horizontal location of the earthquake and perform a grid search in depth to determine the source mechanism at each point by fitting the synthetic and observed waveforms. This new method is verified by a synthetic test with noise added to the synthetic waveforms and a realistic station distribution. We apply this method to a series of Mw3.4-5.6 earthquakes in the Longmenshan fault （LMSF） zone, a region with rugged topography between the eastern margin of the Tibetan plateau and the western part of the Sichuan basin. The results show that our solutions result in improved waveform fits compared to the source parameters from the catalogs we used and the location can be better constrained than the amplitude-only approach. Furthermore, the source solutions with realistic topography provide a better fit to the observed waveforms than those without the topography, indicating the need to take the topography into account in regions with rugged topography.展开更多
基金supported by the Major National Basic Research Program of China (973 Program) on Global Change (Grant No.2010CB951902)the National Natural Science Foundation of China (Grant Nos. 40625014,40705025,40921003,and 41005044)
文摘In this study, records from a 3-yr intensified observational experiment at eight stations along the hillside of Seqilashan over the southeastern Tibetan Plateau were analyzed and combined with records at 28 routine observation stations in the Chinese National Meteorological Station Network to investigate the influences of station location on the different diurnal rainfall variations between station records and Tropical Rainfall Measuring Mission （TRMM） data products. The results indicate that the diurnal variation of warm season rainfall is closely related to location of stations. The prevailing nocturnal rainfall peak in observations at routine stations can be largely attributed to the relatively lower location of the stations, which are mostly situated in valleys. The records at Seqilashan stations on hillsides revealed an evident diurnal afternoon peak of warm season rainfall, similar to that indicated by TRMM data. The different diurnal phases between valley and hillside stations are closely related to the orographically induced regional circulations caused by the complex topography over the Tibetan Plateau. The results of this study indicate that the prevailing nocturnal rainfall associated with the relatively lower location of routine observation stations can partially explain the diurnal rainfall variations between observation station records and TRMM data.
文摘An advanced earthquake location technique presented by Prugger and Gendzwill (1988) was introduced in this paper. Its characteristics are: 1) adopting the difference between the mean value by observed arrival times and the mean value by calculated travel times as the original reference time of event to calculate the traveltime residuals, thus resulting in the 'true' minimum of travel-time residuals; 2) choosing the L1 norm statistic of the residuals that is more suitable to earthquake location; 3) using a simplex optimized algorithm to search for the minimum residual value directly and iteratively, thus it does not require derivative calculations and avoids matrix inversions, it can be used for any velocity structures and different network systems and can solve out hypocentral parameters (λ, ,h) rapidly and exactly; 4) original time is further derived alone, so the trade-off between focal depth and original time is avoided. All these prominent features make us obtain more accurate Tibetan earthquake locations in the rare network condition by using this method. In this paper, we examined these schemes for our mobile and permanent networks in Tibet with artificial data sets,then using these methods, we determined the hypocentral parameters of partial events observed in the field work period of this project from July 1991 to September 1991 and the seven problematic earthquakes during 1989 - 1990. The hypocentral location errors may be estimated to be less than 3. 6 km approximately. The events with focal depth more than 40 km seem to be distributed in parallel to Qinghai-Sichuan-Yunnan arc structural zone.
基金supported by National Natural Science Foundation of China (Grants No.41374056)the Fundamental Research Funds for the Central Universities (WK2080000053)
文摘With dense seismic arrays and advanced imaging methods, regional three-dimensional （3D） Earth models have become more accurate. It is now increasingly feasible and advantageous to use a 3D Earth model to better locate earthquakes and invert their source mechanisms by fitting synthetics to observed waveforms. In this study, we develop an approach to determine both the earthquake location and source mechanism from waveform information. The observed waveforms are filtered in different frequency bands and separated into windows for the individual phases. Instead of picking the arrival times, the traveltime differences are measured by cross-correlation between synthetic waveforms based on the 3D Earth model and observed waveforms. The earthquake location is determined by minimizing the cross-correlation traveltime differences. We then fix the horizontal location of the earthquake and perform a grid search in depth to determine the source mechanism at each point by fitting the synthetic and observed waveforms. This new method is verified by a synthetic test with noise added to the synthetic waveforms and a realistic station distribution. We apply this method to a series of Mw3.4-5.6 earthquakes in the Longmenshan fault （LMSF） zone, a region with rugged topography between the eastern margin of the Tibetan plateau and the western part of the Sichuan basin. The results show that our solutions result in improved waveform fits compared to the source parameters from the catalogs we used and the location can be better constrained than the amplitude-only approach. Furthermore, the source solutions with realistic topography provide a better fit to the observed waveforms than those without the topography, indicating the need to take the topography into account in regions with rugged topography.
