THE VISIBLE EARTHQUAKE FOCAL RELICS OF 7.0 MAGNITUDE EARTHQUAKE OCCURRED IN 216.8MA IN EAST QINLING MOUNTAINS, CHINA

Earthquake Forecasting is recognized as a worldwide enormous scientific chanllenge,.However earthquake focal is very difficult to be directly observed and studied,which makes Seismogenesis research even harder.

Based on the fact of field geological exploration,engineering exposure,geophysical probe etc.an ancient earthquake focal relics has been found in Xionger mountain of the China East Qinling,which formed in 216.8±4Ma (isochron age is 227±8.4Ma) but now appearing on land surface by crustal uplift and wearthering denudation. Combined with the characteristics analysis of cryptoexplosion pipes, series of concealed explosive breccia, rock geochemistry, isotope tracer, isotopic dating, REE, gas-liquid inclusions, and the macroscopic and microscopic crushing characteristics of breccia show that the ancient earthquake focal relics has been formed by a strong hidden explosion in the deep crust on the collision and docking of late Indosinian orogeny between Yangzi plate and north China Plate.The hidden explosion was caused by derivatives of I-type granites magma crystallization differentiation which melt by upper mantle or lower crust through orogeny squeeze, in upwelling process generated high temperature and pressure gas-liquid-supercritical fluid by the crystallization differentiation and reduced pressure boiling,the supercritical fluid and expansion pressure accumulate in weak parts of the enclosed silicified space such as fracture or cracks ect,when the enormous expansion pressure of supercritical fluid exceeds bearing pressure of the depths of static pressure and broken rock strength.

According to the date of the thickness of the overlying strata,eruption ages and depth of the referenced plutonic rock’s , modern relative height contraction, modern outcrops scale of the main shock, and the experimental data of underground nuclear explosions estimate that the cryptoexplosion depth of the earthquake focal relics was located 10km below the surface, the major earthquakes, forming cryptoexplosion energy is about 1.55 × 10¹⁷J, corresponding main earthquake’s surface wave magnitude MS is about 7.0.

This is not only an entity visible earthquake focal relics, but also a complete and consistent one, such as the focal depth, the occurrence time and the intensity of the earthquake.