On Earth’s surface, there are only a handful of high-quality astronomical sites that meet the requirements for very large next-generation facilities. In the context of scientific opportunities in time-domain astronomy, a good site on the Tibetan Plateau will bridge the longitudinal gap between the known best sites1,2 (all in the Western Hemisphere). The Tibetan Plateau is the highest plateau on Earth, with an average elevation of over 4,000 metres, and thus potentially provides very good opportunities for astronomy and particle astrophysics3–5. Here we report the results of three years of monitoring of testing an area at a local summit on Saishiteng Mountain near Lenghu Town in Qinghai Province. The altitudes of the potential locations are between 4,200 and 4,500 metres. An area of over 100,000 square kilometres surrounding Lenghu Town has a lower altitude of below 3,000 metres, with an extremely arid climate and unusually clear local sky (day and night)6. Of the nights at the site, 70 per cent have clear, photometric conditions, with a median seeing of 0.75 arcseconds. The median night temperature variation is only 2.4 degrees Celsius, indicating very stable local surface air. The precipitable water vapour is lower than 2 millimetres for 55 per cent of the night.

Stress relaxation experiments are reported that culminate in energetic failure in rocks analogous to the loading cycle and subsequent localization or reactivation on brittle faults embedded in an elastic medium. Universally, rapid primary deformation arrests and transitions into a long secondary deformation phase that ultimately accelerates to catastrophic rupture. Primary deformation (u) conforms to Andrade's law as du/dt~(t c À t 0 )θ with a standard exponent of 2/3. In the long, and readily observable, secondary phase, the samples both deform and analogously shed load near linearly in time. This stress relaxation rate exhibits a robust power law dependency with time-to-rupture and exhibits the same 2/3 power law exponent observed in the primary phase. Similarly, the brittle strain energy released in the tertiary collapse scales with a normalized secondary stress relaxation rate. Together, these observations suggest a way to predict both the timing of rupture and its energetics from the observed stress (or strain) rate during the secondary relaxation stage.

SONG is a global ground based network of 1 meter telescopes for stellar time-domain science, an international collaboration involving many countries across the world. In order to enable a favourable duty cycle, the SONG network plans to create a homogeneous distribution of 4 nodes in each of the northern and southern hemispheres. A natural possibility was building one of the northern nodes in East Asia, preferably on the Qinghai-Tibetan Plateau. During the last decade, a great deal of effort has been invested in searching for high a quality site for ground based astronomy in China, since this has been one of the major concerns for the development of Chinese astronomy. A number of sites on the plateau have been in operation for many years, but most of them are used only for radio astronomy, as well as small optical telescopes for applied astronomy. Several potential sites for large optical instruments have been identified by the plateau site survey, but as yet none of them have been adequately quantitatively characterised. Here we present results from a detailed multi-year study of the Delingha site, which was eventually selected for the SONG-China node. We also describe the site monitoring system that will allow an isolated SONG and 50BiN node to operate safely in an automated mode.-2nodes which aims to study edge-cutting problems, namely determining detailed internal structures of oscillating stars and looking for Earth-like planetary systems revealed by micro-lensing events. In order to achieve a high duty cycle within a limited budget and to produce homogenous data, a network of identical 1 meter telescope and instruments is planned, which includes 4 nodes almost homogeneously distributed in geographic latitude on each hemisphere (Grundahl et al. 2008). To form such a network in the north, one node must be located in East Asia. Then it is straightforward to plan the remaining 3 sites, in terms of geographic distribution and site quality, in the Canary Islands, the Hawaiian islands and the western Pacific coast of the US. However, due to the global climate pattern, it is unclear whether East Asia is likely to contain a site that can match the quality of those other three oustanding locations, which is necessary to optimize the network's duty-cycle. The Qinghai-Tibetan Plateau provides our best chance to find a site that can deliver data of both quality and quantity that matches the other nodes.During the last decade, the search for a high quality site for ground based astronomy has been one of the major concerns for the development of general-purpose astronomy in China. A great deal of effort has been invested towards this goal over recent years. Since the Qinghai-Tibetan Plateau has a high altitude, dry climate and obviously low light pollution, it has naturally been searched for future high-quality sites. A specific research group to perform site surveys in the west land of western China has been organized (Yao 2005). Some sites, including Oma and Ali, were then selected for detailed site testing measurements...

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