Paleoearthquake rupture behavior and recurrence of great earthquakes along the Haiyuan fault, northwestern China

Abstract

It is generally accepted that crustal earthquakes are caused by sudden displacement along faults, which rely on two primary conditions. One is that the fault has a high degree of synergism, so that once the stress threshold is reached, fault segments can be connected rapidly to facilitate fast slip of longer fault sections. The other is sufficient strain accumulated at some portions of the fault which can overcome resistance to slip of the highstrength portions of the fault. Investigations to such processes would help explore how to detect shortterm and impending precursors prior to earthquakes. A simulation study on instability of a straight fault is conducted in the laboratory. From curves of stress variations, the stress state of the specimen is recognized and the metainstability stage is identified. By comparison of the observational information from the press machine and physical parameters of the fields on the sample, this work reveals differences of temporalspatial evolution processes of fault stress in the stages of stress deviating from linearity and metainstability. The results show that due to in teraction between distinct portions of the fault, their independent activities turn gradually into a synergetic activity, and the degree of such synergism is an indicator for the stress state of the fault. This synergetic process of fault activity includes three stages: generation, expansion and increase amount of strain release patches, and connection between them.. The first stage begins when the stress curve deviates from linearity, different strain variations occur at every portions of the fault, resulting in isolated areas of stress release and strain accumulation. The second stage is associated with quasistatic instability of the early metainstability when isolated strain release areas of the fault increase and stable expansion proceeds. And the third stage corresponds to the late metainstability, i.e. quasidynamic instability as both the expansion of strain release areas and rise of strain level of strain accumulation areas are accelerated. The synergism is accelerated when the quasistatic expansion transforms into quasidynamic expansion, with interaction between fault segments as its mechanism. The essence of such transformation is that the expansion mechanism has changed, i.e. expansion of isolated fault segments is replaced by linkage of the interacting segments when the fault enters the critical state of a potential earthquake. Based on the experimental re sults, coupled with data on the temporalspatial evolution of earthquakes along the LaohushanMaomaoshan fault, west of the Haiyuan fault zone in northwestern China, the synergism process of this fault before the 6 June 2000 M6.2 earthquake is analyzed. GEODYNAMICS & TECTONOPHYSICS P U B L I S H E D B Y T H E I N S T I T U T E O F T H E E A R T H ' S C R U S T S I B E R I A N B R A N C H O F R U S S I A N A C A D E M Y O F S C I E N C E S T e c t o n o p h y s i c s Ma Jin et al.: Accelerated synergism along a fault… 388Аннотация: Обычно...

Clustering of offsets on the Haiyuan fault and their relationship to paleoearthquakes

“…GPS measurements of 3-5 mm/yr (Zhang et al, 2004;Gan et al, 2005) corroborate well with the geological rate. The recurrence interval is reported to be in a thousand year cycle, which is almost the consensus from previous paleoseismic studies (Zhang et al, 1988b;Gaudemer et al, 1995;Liu et al, 1995;Ran et al, 1997;Ran and Deng, 1998;Min et al, 2001;Zhang et al, 2005;Liu-Zeng et al, 2007), among which Zhang et al (2005) proposed synthesis results from 19 trenches on the Haiyuan fault. Geological studies of the 1920 Haiyuan Ms 8.5 earthquake began in 1921, but 1:50,000 scale geological and active fault mapping was not accomplished until the 1980s.…”

“…The Haiyuan fault then changed to a major left-lateral strike-slip fault in the late Pliocene or early Pleistocene (Burchfiel et al, 1991). Over shorter time scales, researchers have focused on active tectonics studies involving active fault mapping (IGCEA, NBCEA, 1990), fault slip rate evaluation (Zhang et al, 1988a;Lasserre et al, 1999;Li et al, 2009), paleoseismology (Zhang et al, 1988b;Gaudemer et al, 1995;Liu et al, 1995;Ran et al, 1997;Ran and Deng, 1998;Min et al, 2001;Zhang et al, 2005;Liu-Zeng et al, 2007), and the analysis of the 1920 coseismic surface rupture zone (Song et al, 1983;Zhang et al, 1987). Slip rates have also been reported based on modern surveys involving interferometric synthetic aperture radar (InSAR), global positioning system (GPS), and LiDAR (Wang et al, 2003;Gan et al, 2005;Liu et al, 2013;Chen et al, 2014).…”

Late Quaternary left‐lateral slip rate of the Haiyuan fault, northeastern margin of the Tibetan Plateau

“…Individual fault strands mostly trend N60°-65°W and intersect the average strike of fault zone at about 15°, except for F 1 . The Haiyuan fault can be divided into three segments according to fault geometry, geomorphology, and paleoseismology [Zhang et al, 2003].…”

“…Paleoseismological studies conducted at Shaomayin and another site (Caiyuan, about 15 km east of Shaomayin site) by Zhang et al [1988bZhang et al [ , 2003 revealed that the earthquake recurrence interval along the Haiyuan fault is greater than 800 years, and possibly 800 to 1400 years. Ran et al [1997] excavated a series trenches to study horizontal displacement associated with paleoearthquakes only 300 m east of our Gaowanzi site.…”

Self-organizing dual clustering considering spatial analysis and hybrid distance measures

“…However, in many real applications, non-spatial attributes are of most concern to users [17][18][19][20]. In a spatial database with non-spatial attributes, data points that are similar to each other in their non-spatial attributes may be scattered geometrically.…”