Source Process of the 1911M8.0 Chon-Kemin Earthquake: Investigation Results by Analogue Seismic Records

kulikova, galina ; kruger, frank;

Several destructive earthquakes have occurred in Tien-Shan region at the beginning of 20th century. However, the detailed seismological characteristics, especially source parameters of those earthquakes are still poorly investigated. The Chon-Kemin earthquake is the strongest instrumentally recorded earthquake in the Tien-Shan region. This earthquake has produced an approximately 200 km long system of surface ruptures along Kemin-Chilik fault zone and killed about∼400 people. Several studies presented the different information on the earthquake epicentre location and magnitude, and two different focal mechanisms were also published. The reason for the limited knowledge of the source parameters for the Chon-Kemin earthquake is the complexity of old analogue records processing, digitization and analysis. In this study the data from 23 seismic stations worldwide were collected and digitized. The earthquake epicentre was relocated to 42.996N◦ and 77.367E◦, the hypocentre depth is estimated between
10 and 20 km. The magnitude was recalculated to mB 8.05, Ms 7.94 and Mw 8.02. The focal mechanism, determined from amplitude ratios comparison of the observed and synthetic seismograms, was: str = 264◦, dip = 52◦, rake = 98◦. The apparent source time duration was
between ∼45 and ∼70 s, the maximum slip occurred 25 s after the beginning of the rupture. Two subevents were clearly detected from the waveforms with the scalar moment ratio between them of about 13
, the third subevent was also detected with less certainty. Taking into account surface rupture information, the fault geometry model with three patches was proposed. Based on scaling relations we conclude that the total rupture length was between ∼260 and 300 km and a maximum rupture width could reach ∼70 km.