Earthquake Environmental Effects of the 1992 MS7.3 Suusamyr Earthquake, Kyrgyzstan, and Their Implications for Paleo-Earthquake Studies

Abstract

Large pre-historical earthquakes leave traces in the geological and geomorphological record, such as primary and secondary surface ruptures and mass movements, which are the only means to estimate their magnitudes. These environmental earthquake effects (EEEs) can be calibrated using recent seismic events and the Environmental Seismic Intensity Scale (ESI2007). We apply the ESI2007 scale to the 1992 M S 7.3 Suusamyr Earthquake in the Kyrgyz Tien Shan, because similar studies are sparse in that area and geological setting, and because this earthquake was very peculiar in its primary surface rupture pattern. We analyze literature data on primary and secondary earthquake effects and add our own observations from fieldwork. We show that the ESI2007 distribution differs somewhat from traditional intensity assessments (MSK (Medvedev-Sponheuer-Karnik) and MM (Modified Mercalli)), because of the sparse population in the epicentral area and the spatial distribution of primary and secondary EEEs. However, the ESI2007 scale captures a similar overall pattern of the intensity distribution. We then explore how uncertainties in the identification of primary surface ruptures influence the results of the ESI2007 assignment. Our results highlight the applicability of the ESI2007 scale, even in earthquakes with complex and unusual primary surface rupture patterns.Geosciences 2019, 9, 271 2 of 17 may not be interpreted as a single earthquake. For example, the 2016 Kaikoura Earthquake in New Zealand with a magnitude of M W 7.8 ruptured at least twelve major crustal faults and produced highly variable primary surface ruptures [5]. It is unlikely that such complexity can be understood with paleoseismological methods, and the magnitude of the paleo-earthquake will probably be under-estimated. (iv) Incoherent and anomalous primary surface ruptures can not only be hard to detect, but may also cause problems when it comes to applying the empirical relationships. For example, the 1992 M S 7.3 Suusamyr Earthquake, Kyrgyzstan, broke the surface in two short sets of primary ruptures with a 25 km gap in between [6,7].One approach to overcome the problem of estimating paleo-earthquake magnitudes based solely on primary surface ruptures is the application of the Environmental Seismic Intensity Scale, ESI2007 [8][9][10]. In contrast to classical intensity scales, such as MSK (Medvedev-Sponheuer-Karnik) or MM (Modified Mercalli), the ESI2007 only uses effects on the environment to assign earthquake intensities. It, therefore, avoids the influence of building styles and the problem of saturation at high intensities, and allows applying the scale to paleo-earthquakes. The conversion of ESI2007 intensities to magnitudes, however, can only be based on a large set of modern case studies, which are currently being collected in the Earthquake Environmental Effects (EEE) catalogue hosted by ISPRA [11]. Preferably, this set of case studies should include earthquakes with different mechanisms, magnitudes, depths, tectonic and geological settings, distribute...

Intensity Reassessment of the 2017 Pohang Earthquake Mw = 5.4 (South Korea) Using ESI-07 Scale

“…This raises concerns for areas with unconsolidated soil deposits and potential areas for liquefaction or areas having potential for slope failure. Therefore, the compilation and documentation of ground effects emerge as a very useful tool in seismic hazard assessment, particularly in land-use planning for sites for future urban centers or areas with critical life-line facilities [27,[39][40][41].…”

“…Several case studies have been reported in the literature of estimating the seismic intensity for historical and modern seismic events around the globe [10,16,[21][22][23][24][25][26]. Despite having the upper hand over traditional intensity scales, the ESI-07 scale only has a limited number of entries from Asia or Central Asia [9,25,27].…”

New Perspectives in the Definition/Evaluation of Seismic Hazard through Analysis of the Environmental Effects Induced by Earthquakes

“…Therefore, the incorporation of the environmental geological effects into the probabilistic/deterministic hazard analysis appears to be mandatory in order to achieve a more accurate seismic hazard estimation. The paper "Earthquake Environmental Effects of the 1992 M S = 7.3 Suusamyr Earthquake, Kyrgyzstan, and Their Implications for Paleo-Earthquake Studies" by C. Grützner et al [10] presents the application of the ESI-07 scale to the 1992 M S = 7.3 Suusamyr Earthquake in the Kyrgyz Tien Shan. The author shows that the ESI-2007 intensity values distribution differs somewhat from traditional intensity assessments Medvedev-Sponheuer-Karnik (MSK) and Modified Mercalli Intensity scale (MMI), because of the sparse population in the epicentral area and the spatial distribution of primary and secondary Environmental Earthquake Effects (EEEs).…”

Use of Macroseismic Intensity Data to Validate a Regionally Adjustable Ground Motion Prediction Model

“…Thus, prehistorical events that are not within the scope of any historical archives can be covered. The basic idea of the ESI is to make use of traces of geological and/or geomorphological nature that have been left behind by primary and secondary surface ruptures and mass movements, so generated by large magnitude earthquakes to post-estimate the intensity of the hazard and the magnitude of the event [71]. Example applications of the ESI scale can be found in references [71][72][73][74][75].…”

“…The basic idea of the ESI is to make use of traces of geological and/or geomorphological nature that have been left behind by primary and secondary surface ruptures and mass movements, so generated by large magnitude earthquakes to post-estimate the intensity of the hazard and the magnitude of the event [71]. Example applications of the ESI scale can be found in references [71][72][73][74][75]. Results reported in reference [73] indicate that incorporating ESI data into probabilistic/deterministic seismic hazard analysis can result in significant changes to the modelled PGA values.…”