Progress of research on anomalies of astronomical time and latitude observations before earthquake

WANG Bo 0 YIN ZhiQiang 0 HAN YanBen 0 0 National Astronomical Observatories, Chinese Academy of Sciences , Beijing 100012, China This paper introduces the discovery of the phenomenon that short-term anomalous fluctuations appeared in residuals of astronomical time and latitude observations before earthquakes and the progress of related researches carried out for many years. The relations between the anomalous variations of time and latitude residuals of astronomical time and latitude instruments in different regions and the earthquakes around these instruments as well as the characteristics of residuals' anomalous variations are analyzed. The significance of the anomalous fluctuations in residuals of astronomical time and latitude caused by the anomalous variations of the local plumb line before earthquake and detecting the vertical variation with astronomical time and latitude observations as well as the importance of carrying out further researches are discoursed. The possibility that the phenomenon will become an effective short-term earthquakes precursor, the current situations and the problems to be solved, are discussed. Also we offer the proposals to develop new roboticized astrometric instruments with high-precision and set up test observation networks in earthquake-prone areas in order to do research in-depth, optimize methods of observing and extracting anomalous information for short-term earthquake prediction, and so on. - Earthquake is one of the most serious natural disasters. A strong earthquake may create a large number of casualties and huge property losses. The earthquakes, which occurred in Tangshan of China in 1976, in Indonesia in 2004, in Wenchuan of China in 2008, in Haiti in 2010 and in Fukushima of Japan in 2011 all brought about huge disasters. Accurate and timely earthquake prediction is the effective means to mitigate earthquake disaster, especially to reduce casualties. The crustal structure and geotectonic movement are very complex. There is an extremely complex geophysical process during the gestation and occurrence of earthquake. So it is still very difficult to detect the movement and variation of ground mass. Although institutes and researchers in many countries are committed to earthquake observations and researches for many years, modern sciences level of comprehending the process of earthquake gestation as well as occurrence and the law of earthquake occurrence is still very shallow. So earthquake research, especially earthquake prediction, is accepted as a worldwide difficult scientific problem, even some researchers hold that earthquake could not be predicted [1]. However, more researchers believe that, by continuous studies, the law of the occurrence of earthquake can be recognized gradually and earthquake can be predicted. Many scholars continuously carry out the researches and attempt to find valuable precursory phenomena and earthquake prediction methods, although there will be a long and tough way to go [25]. Not long after the strong earthquake of M=7.8 in Tangshan in 1976, Zhang and Li et al. astronomers of Beijing Astronomical Observatory (the predecessor of the National Astronomical Observatories) analyzed the astronomical time and latitude observations obtained by visual astrolabe a classical astrometric instrument (relative to the later new technique such as VLBI, SLR, the former ground astromet The Author(s) 2012. This article is published with open access at Springerlink.com ric instruments, such as astrolabe, zenith telescope, zenith tube, are called classical instruments) of the observatory and found anomalous fluctuations appeared in astronomical time and latitude residuals (ATLR) before the major earthquake. They analyzed the data of classical astrometric instruments and vicinal earthquakes in other countries, and found similar phenomena appeared on the eve of many earthquakes [6]. The classical instruments take the local plumb line (direction of gravity field) as observation reference. They thought the anomalous variation of the local plumb line due to the motion of the ground mass before earthquake might be the main reason of the anomalies in ATLR [7]. The result has been submitted to the 19th Generally Assembly of the International Astronomical Union (IAU) in 1985. The 19th Committee (Earth Rotation Committee) pointed out that classical astrometric observations of latitude and universal time might be valuable for studying geophysical phenomena [8]. The significance of optical astrometric observations in research of variation of the plumb line was emphasized by the 19th commission of IAU again in 1991 [9]. During these years, Chinese researchers continued to carry out a series of studies, and proposed to set up observation networks to do further systemic researches to form a new method for providing earthquake prediction information [1030]. However, because of the lack of funding and instruments, observation networks could not be set up. It is a progressive process for people to understand the characteristics of any natural phenomena even the process will be very long due to the complexity of the phenomena and the restrictions of the science and technology development level in corresponding period. However, only by continuous research, will the characteristics of these natural phenomena gradually be understood. Therefore, research on the characteristics of earthquake and earthquake forecasting methods should be carried out continuously, which is extremely important for the development and progress of human society. It is always a question considered by some astronomers and seismologists continuously how to develop the short-term anomaly of ATLR before earthquake to become an effective earthquake precursor. This paper will briefly introduce the discovery and the progress of related researches about this phenomenon as well as the problems should be solved to develop the phenomenon to become an effective earthquake precursor, and offer our proposals for how to develop the research deeply and to do earthquake prediction test. 1 Significance and research progress of ATLR anomaly before earthquake 1.1 Discovery of the anomalous ATLR phenomenon celestial sphere due to the rotation of the earth with dedicated classical astrometric telescopes, calculating the variation of the earths rotation rate, that is the variation of the universal time UT (denoted by UT1UTc) and variation of observation stations latitude, and getting the information of the earths polar motion (expressed by polar coordinates X, Y). These data are called Earth rotation parameters (ERP). The dedicated international organization (in early stage it was International Latitude ServesILS, later were Bureau International de IHeureBIH and International Polar Motion ServesIPMS. Now the International Earth Orientation and Reference Systems ServiceIERS is in charge of these works) to calculate ERP by integrating the observations obtained by the instrume (...truncated)