Geologic hazards associated with seismogenic faulting in southern Siberia and Mongolia: forms and location patterns

Abstract

The forms and location patterns of geologic hazards induced by earthquakes in southern Siberia, Mongolia, and northern Kazakhstan in1950 through 2008 have been investigated statistically, using a database of coseismic effects created as a GIS MapInfo application, with a handy input box for large data arrays. The database includes 689 cases of macroseismic effects from MS=4.1–8.1 events at 398 sites. Statistical analysis of the data has revealed regional relationships between the magnitude of an earthquake and the maximum distance of its environmental effects (soil liquefaction and subsidence, secondary surface rupturing, and slope instability) to the epicenter and to the causative fault. Thus estimated limit distances to the fault for the MS=8.1 largest event are 40km for soil subsidence (sinkholes), 80km for surface rupture, 100km for slope instability (landslides etc.), and 130km for soil liquefaction. These distances are 3.5–5.6 times as short as those to the epicenter, which are 150, 450, 350, and 450km, respectively. Analysis of geohazard locations relative to nearest faults in southern East Siberia shows the distances to be within 2km for sinkholes (60% within 1.5km), 4.5km for landslides (90% within 1.5km), 8km for liquefaction (69% within 1km), and 35.5km for surface rupture (86% within 2km). The frequency of hazardous effects decreases exponentially away from both seismogenic and nearest faults. Cases of soil liquefaction and subsidence are analyzed in more detail in relation to rupture patterns. Equations have been suggested to relate the maximum sizes of secondary structures (sinkholes, dikes, etc.) with the earthquake magnitude and shaking intensity at the site. As a result, a predictive model has been created for locations of geohazard associated with reactivation of seismogenic faults, assuming an arbitrary fault pattern. The obtained results make basis for modeling the distribution of geohazards for the purposes of prediction and estimation of earthquake parameters from secondary deformation.