@article{OuKulikovaYuetal.2020, author = {Ou, Qi and Kulikova, Galina and Yu, Jingxing and Elliott, Austin and Parsons, Bethany and Walker, Richard}, title = {Magnitude of the 1920 Haiyuan earthquake reestimated using seismological and geomorphological methods}, series = {Journal of geophysical research : Solid earth}, volume = {125}, journal = {Journal of geophysical research : Solid earth}, number = {8}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-9313}, doi = {10.1029/2019JB019244}, pages = {28}, year = {2020}, abstract = {Reported magnitudes ranging between 7.8 and 8.7 highlight a confusion about the true size of the 1920 Haiyuan earthquake, the largest earthquake recorded in the northeast Tibetan Plateau. We compiled a global data set of previously unlooked-at historical seismograms and performed modern computational analyses on the digitized seismic records. We found the epicenter to be near Haiyuan town and obtained a moment magnitude of M-W=7.90.2. Following traditional approaches, we obtained m(B)=7.90.3 with data from 21 stations and M-S(20)=8.10.2 with data from three stations. Geomorphologically, we mapped the surface rupture and horizontal offsets on high-resolution Pleiades satellite and drone imagery that covered the entire western and middle sections of the 1920 Haiyuan earthquake rupture and compiled offsets reported on the eastern section from field measurements in the 1980s. Careful discrimination between single-event and cumulative offsets suggests average horizontal slips of 3.01.0m on the western section, 4.51.5m on the middle section, and 3.5 +/- 0.5m on the eastern section, indicating a total moment magnitude of M-W=7.8 +/- 0.1. Thus, the seismological and geomorphological results agree within the uncertainties, a weighted average giving a moment magnitude of M-W=7.9 +/- 0.2 for the 1920 Haiyuan earthquake. It is likely that earthquake magnitudes based on the historical M were systematically overestimated.
Plain Language Summary Earthquakes are the main mechanism by which elastic energy accumulating due to tectonic motion is released. As the earthquake magnitude scale is logarithmic, major earthquakes control the bulk of this energy budget and are often the most destructive, like the 1920 Haiyuan earthquake with similar to 230,000 casualties. However, major earthquakes tend to have recurrence periods of several hundred years, longer than our instrumental records. To obtain knowledge of historic major earthquakes, paleoseismologists measure geomorphic offsets and map surface ruptures left by past events and estimate the shaking intensity from historical writings. However, in the case of the Haiyuan earthquake, which happened in the late historic, early instrumental period, the magnitudes reported from these two communities differed significantly. In order to constrain the magnitude of this earthquake for seismic hazard assessment and to reconcile the differences between published magnitudes, we reestimated its magnitude from both newly compiled and digitized seismological records and modern satellite and drone imagery. The results show that the early seismological magnitudes were overestimated, which may affect historical magnitudes systematically. The 1920 Haiyuan earthquake was of a similar magnitude to the 2001 Kokoxili and 2008 Wenchuan earthquakes that also occurred in and around the Tibetan Plateau, instead of more than half a magnitude larger.}, language = {en} } @article{EigmuellerChaushevGillenetal.2019, author = {Eigm{\"u}ller, Philipp and Chaushev, Alexander and Gillen, Edward and Smith, Alexis and Nielsen, Louise D. and Turner, Oliver and Csizmadia, Szilard and Smalley, Barry and Bayliss, Daniel and Belardi, Claudia and Bouchy, Francois and Burleigh, Matthew R. and Cabrera, Juan and Casewell, Sarah L. and Chazelas, Bruno and Cooke, Benjamin F. and Erikson, Anders and Gansicke, Boris T. and Guenther, Maximilian N. and Goad, Michael R. and Grange, Andrew and Jackman, James A. G. and Jenkins, James S. and McCormac, James and Moyano, Maximiliano and Pollacco, Don and Poppenh{\"a}ger, Katja and Queloz, Didier and Raynard, Liam and Rauer, Heike and Udry, Stephane and Walker, Simon. R. and Watson, Christopher A. and West, Richard G. and Wheatley, Peter J.}, title = {NGTS-5b}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {625}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201935206}, pages = {9}, year = {2019}, abstract = {Context. Planetary population analysis gives us insight into formation and evolution processes. For short-period planets, the sub-Jovian desert has been discussed in recent years with regard to the planet population in the mass/period and radius/period parameter space without taking stellar parameters into account. The Next Generation Transit Survey (NGTS) is optimised for detecting planets in this regime, which allows for further analysis of the sub-Jovian desert. Aims. With high-precision photometric surveys (e.g. with NGTS and TESS), which aim to detect short period planets especially around M/K-type host stars, stellar parameters need to be accounted for when empirical data are compared to model predictions. Presenting a newly discovered planet at the boundary of the sub-Jovian desert, we analyse its bulk properties and use it to show the properties of exoplanets that border the sub-Jovian desert. Methods. Using NGTS light curve and spectroscopic follow-up observations, we confirm the planetary nature of planet NGTS-5b and determine its mass. Using exoplanet archives, we set the planet in context with other discoveries. Results. NGTS-5b is a short-period planet with an orbital period of 3.3569866 +/- 0.0000026 days. With a mass of 0.229 +/- 0.037 M-Jup and a radius of 1.136 +/- 0.023 R-Jup, it is highly inflated. Its mass places it at the upper boundary of the sub-Jovian desert. Because the host is a K2 dwarf, we need to account for the stellar parameters when NGTS-5b is analysed with regard to planet populations. Conclusions. With red-sensitive surveys (e.g. with NGTS and TESS), we expect many more planets around late-type stars to be detected. An empirical analysis of the sub-Jovian desert should therefore take stellar parameters into account.}, language = {en} } @article{WalkerBoyntonShpritsetal.2022, author = {Walker, Simon N. and Boynton, Richard J. and Shprits, Yuri Y. and Balikhin, Michael A. and Drozdov, Alexander}, title = {Forecast of the energetic electron environment of the radiation belts}, series = {Space Weather: The International Journal of Research and Applications}, volume = {20}, journal = {Space Weather: The International Journal of Research and Applications}, number = {12}, publisher = {American Geophysical Union}, address = {Washington}, issn = {1542-7390}, doi = {10.1029/2022SW003124}, pages = {21}, year = {2022}, abstract = {Different modeling methodologies possess different strengths and weakness. For instance, data based models may provide superior accuracy but have a limited spatial coverage while physics based models may provide lower accuracy but provide greater spatial coverage. This study investigates the coupling of a data based model of the electron fluxes at geostationary orbit (GEO) with a numerical model of the radiation belt region to improve the resulting forecasts/pastcasts of electron fluxes over the whole radiation belt region. In particular, two coupling methods are investigated. The first assumes an average value for L* for GEO, namely LGEO* L-GEO* = 6.2. The second uses a value of L* that varies with geomagnetic activity, quantified using the Kp index. As the terrestrial magnetic field responds to variations in geomagnetic activity, the value of L* will vary for a specific location. In this coupling method, the value of L* is calculated using the Kp driven Tsyganenko 89c magnetic field model for field line tracing. It is shown that this addition can result in changes in the initialization of the parameters at the Versatile Electron Radiation Belt model outer boundary. Model outputs are compared to Van Allen Probes MagEIS measurements of the electron fluxes in the inner magnetosphere for the March 2015 geomagnetic storm. It is found that the fixed LGEO* L-GEO* coupling method produces a more realistic forecast.}, language = {en} }