Olyutorskii Earthquake Research Articles

Enigma of the Olyutorskii Earthquake Resolved by SAR Interferometry

Enigma of the Olyutorskii Earthquake Resolved by SAR Interferometry

New Data on the Olyutorskii Earthquake Acquired via SAR Interferometry

A coseismic displacement field based on SAR interferometry data was determined for the area of the April 20, 2006 Olyutorskii earthquake. The resulting image shows displacements toward the satellite (“uplifts”) to the northwest of the surface rupture area where the epicenters of most aftershocks lie. The displacement- affected area extends as far as the Vyvenka–Vatyna tectonic suture. We have developed a model for the rupture surface that is in agreement with the hypothesis of A.V. Lander and T.K. Pinegina stating that the largest displacements occurred along a fault northwest of the surface rupture zone; the fault dips southeast and is not exposed. The slip on the fault is close to a pure thrust type. These results furnish another confirmation of the fact that advanced satellite technologies can provide important additional information on the dynamics of seismic regions, especially where the existing observing networks are sparse.

The deep structure of the Olyutorskii earthquake rupture zone in the Koryak Upland: Geophysical evidence

This paper considers the data of magnetotelluric sounding (MTS) and gravity and magnetic surveys, as well as other geological information. We describe the methods that were used in making the observations and for interpretation of MTS data. We focus on incorporating the influence of the shift effect and the coast effect. Generalized geoelectric sections are based on mean longitudinal curves, which are less subject to distortion. Transverse curves were used for fault identification. The geoelectric sections include a sedimentary-volcanogenic layer, a high ohmic crust, and a conductive lithosphere layer. They contain faults that were detected from the divergences between oriented MTS curves and other data. The deep-seated faults in the Vyvenka basin have surface expression in the form of seismotectonic discontinuities that extend for 80 and 140 km. It was found that the hypocenters of the Olyutorskii earthquake and its aftershocks were in the crustal layer above the conductive lithosphere layer. Most aftershock hypocenters are typically situated in the area of the deep fault. We discuss a possible origin of the conductive lithosphere layer and of deep faults.

Structural damage patterns in the villages of Korf and Tilichiki due to the M S 7.7 April 20(21), 2006 Olyutorskii earthquake

The area of the Koryak Autonomous Okrug was hit by an MS 7.7 earthquake on April 20(21), 2006, the largest to have occurred in the area during the period of historical and instrumental observation. This event is now referred to as the Olyutorskii earthquake. We present results from a study of the associated macroseismic effects as observed in the villages of Korf and Tilichiki. The intensity was IX at Korf and VIII at Tilichiki on the MSK-64 scale.

Geodynamic studies of the April 20(21), 2006 Olyutorskii earthquake based on observations by the Kamchatka GPS network

This paper presents results from an analysis of GPS observations made by the Kamchatka regional GPS network (KAMNET) in relation to the Olyutorskii earthquake and plate interaction. The coseismic changes were interpreted for the Olyutorskii earthquake and its largest aftershock (May 22, 2006, MW = 6.6) within the framework of a dislocation source in an elastic half-space.

Water-level changes in the wells of Kamchatka at the time of the M w 7.6, April 20, 2006 Olyutorskii earthquake

The seismic waves excited by the Mw 7.6 Olyutorskii earthquake that occurred on April 20, 2006 in the Koryak Upland gave rise to water-level changes in five wells situated in continental areas of Kamchatka at hypocentral distances of 750–1150 km. We describe the effects due to seismic waves, as well as the water-level anomalies for February–April 2006 before the earthquake. We used an original technique for the processing of water-level records based on the study of barometric and tidal water-level responses in order to estimate the volume strain in water-saturated rocks during synchronous level variations at two wells. We discuss possible mechanisms for producing anomalous water-level changes due to elastic deformation of monitored groundwater reservoirs and to crack dilatancy in the water-saturated rocks.

Macroseismic evaluation of the impact of the Olyutorskii earthquake and its larger aftershocks

This paper presents the results from a macroseismic survey of the impact and consequences of the MW = 7.6 April 20(21), 2006 Olyutorskii earthquake in the area of the Koryak Autonomous Okrug and the adjacent areas in Kamchatka and Magadan regions. The earthquake was felt over an area of about 400000 sq. km with intensities of II to IX–X on the MSK-64 scale. Information was gathered from 37 population centers situated in this area and was used to present a summary of felt effects, to construct an isoseismals map, and to determine the macroseismic magnitude.

The geometry and temporal structure of a high frequency source: The Olyutorskii earthquake of April 20, 2006

We have determined the parameters of the high frequency radiator for the M W = 7.6, April 20, 2006 Olyutorskii earthquake using P-wave high frequency power signal (HFPS), as recorded at 57 distant stations. Our data processing was done, first, to correct the HFPSs by inverse filtering using the aftershock HFPS as an empirical power Green’s function. In this way, we found the source HFPS for each station, separately for the frequency bands 0.7–1.7 and 1.5–2.5 Hz. These data were used to determine parameters of the radiator model as a segment with the rupture propagating to both sides of the hypocenter at constant velocity. The parameters are as follows: length 128 ± 52 km, the strike of the longer arm of the rupture 225° ± 19° SW, the distance from the epicenter to the centroid 23 ± 9 km, and rupture velocity 2.5 ± 0.8 km/s. The rupture was bilateral with a moderate asymmetry. The rupture duration was 35.0 ± 1.6 s for the southwestern arm and about 23 s for the northeastern.

A geological study of the epicentral area of the April 20(21), 2006 Olyutorskii earthquake

Primary and secondary earthquake effects were investigated (surface breakage and felt effects in the villages of Tilichiki, Korf, and Khailino) in the epicentral area of a large earthquake occurring in northern Kamchatka Krai. The primary effects include an extended surface break that can be followed for a length of about 140 km. The secondary (gravitational and vibrational) effects include soil slides and minor rockfalls, snow flows on slopes, resonant cracks, soil liquefaction phenomena consisting of mud cones, mud gryphons, and discharges of soil from cracks. Detailed maps showing the main types of earthquake surface effects have been made. Paleoseismic data show traces of several large earthquakes that have occurred in the Olyutorskii earthquake zone. Radio carbon dating of soil samples from these paleoseismic scarps revealed a history of great earthquakes occurring in Koryakia. In all, four seismic events with magnitudes about that of the 2006 Olyutorskii earthquake have occurred there during 8000 years, the return period of such events being 1000–2500 years.

Estimating the source parameters for the M W 7.6 April 20, 2006 Olyutorskii earthquake from long period P-wave records made by the worldwide network

The source parameters of the MW = 7.6 Olyutorskii earthquake were estimated using the moments of the slip rate function with degrees 1 and 2. The moments were estimated from broadband P-wave records at 52 stations of the worldwide network. The first step was to find a function S(t) for each station; this function is an apparent source time function, i.e., the P-wave slip as radiated by the source toward a station under consideration. The method of empirical Green’s functions was used to estimate S(t). The next step was to calculate the moments of S(t) of degrees 1 and 2 over time and to set up relevant equations to be solved by least squares for the unknown source moments. The horizontal linear source was used as a nonparametric model for calculating the source moments. Haskell’s parametric model was used for further interpretation of the source moments. The resulting estimates are as follows: the source centroid was 13–25 km southwest of the epicenter, the source was 105–120 km long, the source strike was 222°–228°, the rupture velocity was 2.7–3.0 km/s, and the total radiation duration was 24–27 s. These estimates indicate a bilateral rupture dominated by a southwestward sense of rupture propagation. The source characteristics are consistent with the aftershock area geometry and with the focal mechanism, as well as with surface breakage as observed by geologists in the field.

The Olyutorskii earthquake of April 20, 2006: Organizing surveys, observations, problems, and results

The Olyutorskii earthquake of April 20, 2006: Organizing surveys, observations, problems, and results

The earthquake history of the Koryak Upland and the aftershock process of the M W 7.6 April 20(21), 2006 Olyutorskii earthquake

We investigated the seismicity in the aftershock area of a great earthquake occurring on April 20, 2006 (21:04 LT) in the area of the Koryak Autonomous Okrug. This analysis of the aftershock process was based on a complete catalog of the earthquakes that were recorded during April–May 2006 by the regional network of seismic stations operated by the Kamchatka Branch of the Geophysical Service of the Russian Academy of Sciences. We also made use of a catalog of low magnitude events for May 2–17 as recorded by a mobile seismic network deployed in the rupture zone. We provide a review of seismicity for the Koryak Upland for the period of instrumental observations in the 20th and early 21st centuries.

The ground motion excited by the Olyutorskii earthquake of April 20, 2006 and by its aftershocks based on digital recordings

We studied broadband digital records of the MW = 7.6 Olyutorskii earthquake of April 20, 2006 and its aftershocks at local and regional distances. We have made a detailed analysis of data on peak ground motion velocities and accelerations due to aftershocks based on records of two digital seismic stations, Tilichiki (TLC) and Kamenskoe (KAM). The first step in this analysis was to find the station correction for soil effects at TLC station using coda spectra. The correction was applied to the data to convert them to the reference bedrock beneath the Kamenskoe station. The second step involved multiple linear regression to derive average relationshis of peak amplitude to local magnitude ML and distance R for the Koryak Upland conditions. The data scatter about the average relationshis is comparatively low (0.22–0.25 log units). The acceleration amplitudes for ML = 5, R = 25 km are lower by factors of 2–3 compared with those for eastern Kamchatka, the western US, or Japan. A likely cause of this anomaly could be lower stress drops for the aftershocks.