Total Seismic Energy Research Articles

SEISMICITY of TAJIKISTAN and ADJACENT TERRITORIES in 2015

The seismic monitoring system consisting of seven digital stations continued to operate in Tajikistan in 2015. This network has registered 9071 earthquakes with KR=8.6–17.0, 6427 of which were Pamir-Hindu Kush earthquakes with intermediate depths (h=70–300 km), and 2644 were shallow events. The total seismic energy released was E=1.8151017 J. The strongest for 2015 was the Hindu Kush earthquake on Octo-ber 26 with Mw=7.5, h=230 km (hpP=217 km) that occurred near the southern borders of the Republic. This earthquake caused significant damage and the death of at least 115 people. It was felt on the territory of 14 states, with a total shaking area of more than 14106 km2. A detailed isoseismal map of this earthquake is given for the Tajikistan territory only. The earthquake was accompanied by a series of over 1400 aftershocks with KR=8.6–12.8, unexpectedly numerous for a deep earthquake. Within the borders of the Republic, the Sarez-II earthquake occurred near the Lake of Sarez on December 7 with Mw=7.2, h=20 km, I0=8, was the strongest one. Undoubtedly, it was triggered by the Hindu Kush earthquake on October 26. In total, more than 500 houses were damaged, dozens of people were injured, and there were human casualties. A detailed isoseismal map of this earthquake was made for four levels of intensity – I=7, 6, 5 and 4. The number of its aftershocks for 24 days only was 1342, with KR=8.6–13.9. As a result the level of seismicity in Tajikistan in 2015, both in terms of the number of earthquakes and the level of released seismic energy, was the highest during the period of instrumental observations.

SEISMICITY of the ALTAI and SAYAN region in 2015

A review of seismicity of the Altai and Sayan region in 2015 is presented. The stationary network of seismic stations included 52 stations. Compared to 2014, four new seismic stations were added in the region. Additionally, two local temporary networks including 37 temporary seismic stations operated in the region. 6206 earthquakes were recorded with a total seismic energy of 5.97•1012 J. A brief description of the seismicity in the Chui-Kurai zone of the Altai Mountains is given.

SEISMICITY of the NORTH-EAST of RUSSIA in 2015

The results of seismic monitoring of the Magadan oblast, the Chukotka Autonomous okrug, and the shelves of the adjacent seas (Okhotsk, Chukchi, Bering, and East Siberian seas) are considered. There were 14 seismic stations working in the region. The new station “Gadlya” was opened on the Okhotsk sea coast. The catalog includes information about 290 earthquakes with energy classes KR=4.4–12.6. As usual, most of them (93 %) are localized in the Kolyma region. The total seismic energy released within the region’s borders was ΣЕ=4.6341012 J. According to the earthquake energy completeness map Кmin built for the region, minimal energy level of earthquakes, Кmin=5.0, is provided at two areas near the Susuman and Magadan stations. The station network can register without omissions the earthquakes with Kmin≥8 at the Okhotsk sea and Kolyma areas, with Kmin≥10.6 in the Chukotka area. In 2015 three earthquakes with intensities I=2–4 by MSK-64 scale were felt in settlements of North East of Russia. The 2015 strongest earthquake occurred on June 1 at 10h53m with KR=12.6 (MPSP=4.9), h=31 km in the Kolyma area. A maximum shaking intensity of I=4 was observed in Omsukchan settlement (∆=132 km). In March 2015 a swarm of 29 weak earthquakes with KR=6.2–9.8 occurred northeast of Talaya settlement. Epicenters of Kolyma area earthquakes were plotted on the tectonic zoning map of the Magadan region. Most earthquakes are confined to the main deep faults oriented in the northeastern and sublatitudinal directions. All hypocenters are located within the Earth's crust. The seismicity level of the North-East of Russia in 2015 according to the “SOUS09” scale was assessed as "background average" for the observation period from 1968 to 2015. Spatially, all earthquakes in the North-East of Russia are traditionally concentrated within the major seismogenic belts – Chersky, North-Okhotsk, and Trans-Beringian.

Seismotectonic analysis of the Viraayots–Karabakh zone (Armenia) and the adjacent areas of Lesser Caucasus

The territory of Armenia, although relatively small, is geologically and tectonically complex. Its complexity is not only due to a dense network of faults. It results from a complicated history of tectonic development including several phases of mountain formation and planation, and the extensive development of fold-block, tectonic and magmatic processes. An important scientific task is identification of earthquake-prone structural blocks by analysing seismotectonic data on geotectonic zones in Armenia. This article describes the seismotectonic analysis of geological and geophysical data on the Viraayots-Karabakh zone.We used a wide spectrum of modern tectonic-geomorphological indices and GIS technologies in order to assess the neotectonic (Neogene – Quaternary) activity of the main block units of the study area and to classify the block units by their tectonic activity levels. Tectonics of the study area is contrasting, and many tectonically active blocks are in the immediate neighbourhood with passive blocks.Based on the records of seismic events of various magnitudes and historic earthquake data, we analysed modern seismicity of the block units. For each block, a quantitative analysis of its total seismic energy release was performed, and relationships between the released seismic energy values and the number of recorded earthquakes were analyzed. Based on such analysis, we identify a group of blocks wherein the total released seismic energy values are high, but the numbers of seismic events recorded in these blocks are rather limited. In the context of block tectonic activity, analysing these data makes it possible to detect the blocks with the highest probability of the occurrence of strong earthquakes.

Seismic Response of RC Frames with a Soft First Story Retrofitted with Hysteretic Dampers under Near-Fault Earthquakes

Reinforced concrete (RC) frame structures with open first stories and masonry infill walls at the upper stories are very common in seismic areas. Under strong earthquakes, most of the energy dissipation demand imposed by the earthquake concentrates in the first story, and this eventually leads the building to collapse. A very efficient and cost-effective solution for the seismic upgrading of this type of structure consists of installing hysteretic dampers in the first story. This paper investigates the response of RC soft-story frames retrofitted with hysteretic dampers subjected to near-fault ground motions in terms of maximum displacements and lateral seismic forces and compares them with those obtained by far-field earthquakes. It is found that for similar levels of total seismic input energy, the maximum displacements in the first story caused by near-fault earthquakes are about 1.3 times larger than those under far-field earthquakes, while the maximum inter-story drift in the upper stories and the distribution and values of the lateral forces are scarcely affected. It is concluded that the maximum displacements can be easily predicted from the energy balance of the structure by using appropriate values for the parameter that reflects the influence of the impulsivity of the ground motion: the so-called equivalent number of cycles.

Derivation of yield force coefficient for RC frames considering energy balance and P-delta effects

Currently, prominent energy balance concept can efficiently be used to calculate the yield base shear force of structures. Energy balance equation is an additional constraint for the balance of seismic input energy by the energy absorption of the structure. This equation can be defined as the sum of elastic and plastic energies of structural systems using elastic and plastic load-deformation characteristics and the total energy dissipation capacity can finally be equated to the seismic energy demand. The objective of this paper is to present a procedure for the determination of energy-based yield force coefficient of reinforced concrete (RC) frame structures considering P-delta effects. The total of elastic and plastic energies are computed by means of elastic spectral velocity and energy modification factor, which is originally derived for structural systems with geometric nonlinearity. Total inelastic energy of single-degree-of-freedom (SDOF) system is transformed into the total inelastic energy of the multi-degree-of-freedom (MDOF) system using the conversion based on structural dynamics. Plastic energy of MDOF system is formulated after total seismic energy demand is obtained. It is accordingly equated to the total work done by inelastic MDOF structure with P-delta effects and consequently, a dimensionless yield force coefficient is derived. Nonlinear static analyses are performed for selected multi-story RC frames and yield force coefficients are compared with the results of the energy-based formulation. The results show that the proposed formulation taking P-delta effects into account can be effectively used to estimate the yield force coefficient of RC frame structures.

KURIL-OKHOTSK REGION

The review of the Kuril-Okhotsk region seismicity in 2014 is presented. Earthquake parameters were obtained on the basis of the data of the seismic stations of Sakhalin branch GS RAS and the data of neighboring seismological Russian and foreign agencies. 83.6 % of earthquakes are located within the depth interval of h80 km, 13.5 %  within the intermediate layer h=81–300 km, 2.9 % of earthquakes have depths h>300 km; the maximum depth of the hypocenter was h=559 km. The analysis of the seismic situation in 2014 in comparison with the data for 2001–2013 is carried out, a description of the seismic situation in seismically active regions is given. For 30 earthquakes information was obtained on the macroseismic effect in Russia, the maximum intensity did not exceed Ii=5; for 50 earthquakes there was information on the intensity in the territory of the Japanese Islands, the maximum value was Ii =67 by the MSK-64 scale. The strongest earthquake in the region occurred in the central part of the Sea of Okhotsk on September 18 at 04h17m with h=529 km and MSH=6.2. Its focal mechanism is classified as an incision with a small right-lateral strike-slip component along a subvertical plane of north-eastern strike. The seismicity of the region in 2014 can be considered as a moderate, the number of earthquakes with a magnitude MP≥4.5 and their total seismic energy do not exceed the average values over a 13-year period, the level of seismicity of the region according to the SOUS’09 method is classified as а “background average”. The distribution of earthquake hypocenters and their focal mechanisms show that most of the earthquakes in the Kuril-Okhotsk region relate to the process of the subduction of the Pacific lithospheric plate under the Okhotsk Sea plate.

NORTH-EAST OF RUSSIA

The results of seismic monitoring of Magadan region, Chukotka Autonomous Area and adjacent sea shelf (Okhotsk, Chukchi, Bering and East Siberian seas) are given. The information about 12 digital seismic stations and monitoring equipment types and parameters is given. Maps of earthquake energy representativeness, seismic stations and epiсenters are presented. The distribution of earthquake number by energy classes and total seismic energy by six regions of North-East of Russia is given. The information about 234 events with energy classes КР=6.0–12.8 is included in the catalog. All hypocenters are located within the Earth's crust. Earthquake epicenters in Kolyma area are plotted on the tectonic zoning scheme. The strongest earthquake in 2014 with MPSP=4.5 (КР=12.8) occurred on July 4 in Kolyma area and was called Elgenskoe II. It was sensible with intensity I=4. Monitoring in 2014 showed decrease of seismic activity in Okhotsk sea area and its increase in the Kolyma. Spatially, all the earthquakes of the North-East of Russia are traditionally concentrated within the large seismogenic zones: the Chersky, the North Okhotsk and the Trans-Bering Sea.

CARPATHIANS

The article describes seismic observations in the Carpathian region in 2014, which were carried out, as before, by two organizations from two states: in Ukraine – the Seismicity Department of the Carpathian region of the Institute of Geophysics of the National Academy of Sciences of Ukraine, in Moldova – the Seismology Laboratory of the Institute of Geology and Seismology of the Academy of Sciences of Moldova. In Ukraine, 20 stationary digital stations and 3 temporary ones worked in the Dniester energy complex with a processing center in Lviv, in Moldova - six stations with a center in Chisinau. Different programs, local hodo-graphs and magnitudes were used. The consolidated catalog of earthquakes was created in Lviv. A map of epi-centers and a table of the distribution of earthquakes of different classes by region are given. The total number of earthquakes in 2014 was NΣ=81 in the range KP =5.2–14.3 with the interval of hypocenter depths h=1–154 km and the total seismic energy ΣE=2.11·1014 J. Of these, 18 earthquakes with depths h=77–154 km located in the Vrancea zone. The maximum earthquake with KP=14.3 was registered on November 22 in the Precarpathian Trough with hрР=37 km. In the Vrancha mountains the maximum earthquake occurred on March 29 with the KP=12.5 and hрР=136 km. In the Precarpathian and Transcarpathian regions, all earthquakes were weaker. The most powerful event in Transcarpathia was a perceptible earthquake that occurred near the Trostnyk seismic station on November 15 with KP=8.9. The earthquake source is located in the Earth's crust at a depth of h=10 km. The earthquake was felt by the population of the Dyakovo, Trostnyk, Fanchykovo villages with the intensity of 5 and 4–5. In general, in all the seismically active zones of the Carpathians in 2014, there was a slight increase in the level of seismicity compared to that in 2013.

TAJIKISTAN

In 2014, a seismic monitoring system, restored with the participation of the Swiss government, continued to operate in Tajikistan. Seven digital stations Trident+Trillium-40 devices, provide registration of events located in Tajikistan and hundreds of kilometers beyond. This network recorded 5306 earthquakes with КР=8.6–14.5, of which 4308 are deep-focus Pamir-Hindu Kush earthquakes with h=70–270 km and 998 are shal-low, scattered throughout the territory. The total seismic energy released in the sources of all earthquakes amounted to Е~6.61014 J. Within the borders of the Republic, the most powerful earthquake (with КР=13.3) was on September 13. The earthquake located in the southern spurs of the RushanRange at the end of the system of dual Karakul-Sarez faults dividing the Pamirs into Western and Eastern parts. It was felt with an intensity of Ii=4–5 in Khorog and Roshtkal, Ii=4in Rushan and on the lake Sarez. Shocks with Ii=4–5 from the November 1 earthquake with KP=12.1 were also felt in Rogun, at the site of Rogun hydropower plant under construction. The maximum deepest earthquake (КР=14.5, Mw=5.4, h=200 km) occurred on June 14 in the Afghan subzone. Due to the great depth, the area of its perceptibility Ii=3 amounted to 220 thousand km2 in Tajikistan, Afghanistan, Pakistan and Kyrgyzstan. However,in general the seismic process in the Republic proceeded in the background.

ALTAI and SAYAN

The review of the seismicity in Altai and Sayan region for 2014 is presented. The stationary network of seismic stations included 48 stations. Compared to 2013, seven new seismic stations were added in the region. Additionally 3 local temporary networks including 39 temporary seismic stations operated in the region. 8828 earthquakes were recorded with the total seismic energy of 4.6•1012 J. A brief description of the seismicity in the Chui-Kurai zone of the Altai Mountains is given.

CENTRAL ASIAN GEODYNAMIC REGIMES WEST AND EAST 102–104° GEODIVIDER

Ample geologic and geophysical data provide the basis for distinguishing the 102–104° E geodivider in the North, Central and South Asia. The geodivider’s central part is confirmed by the data on seismicity, seismically active faults and the modern crust block structure. These data and historical and instrumentally identified earthquake epicenters were used for a more correct definition of the block boundaries and interblock zones in the central part of the geodivider and in its wings. Seismic energy is considerably increased (to 10 11 –10 16 J) in the eastern part of the geodivider’s western wing, and rarely increased directly in the geodivider itself. Near the geodivider, a seismic energy increase is detected east of it only at the western border of the South-Eastern China Block. The authors analyzed deep seismic sections and constructed energy dissipation graphs along transects crossing the geodivider and its western wing. The analysis and the graphs show the predomination of left-lateral NW-striking slips in the north, thrusts to the east and southeast in the center, and right-lateral NE-striking slips in the south. The total seismic energy increases constantly to the west. In the central and northern segments of the geodivider’s central part and west of it, horizontal blocks displacements cause a direct influence on seismicity level increasing and changes in geodynamic regimes within the investigated territory of Central Asia. Changes in the horizontal displacement vector are accompanied by the change of tectonic strain regimes. Increased heat flow values to the east from the geodivider within the East Asian transit zone are probably related to the change of the geodynamic regimes in the same direction under the influence of the submerged Pacific slab. The data obtained by the Chinese and Russian researchers confirm delamination (stratification) processes in the Southeast Tibet crust during its interaction with the colder and thicker lithosphere of Southeast China, and displacement of its upper layers to the southeast and south, as we supposed in our earlier publications.

Seismic modeling and inversion using half-precision floating-point numbers

New processors are increasingly supporting half-precision floating-point numbers, often with a significant throughput gain over single-precision operations. Seismic modeling, imaging, and inversion could benefit from such an acceleration, but it is not obvious how the accuracy of the solution can be preserved with a very narrow 16-bit representation. By scaling the finite-difference expression of the isotropic elastic wave equation, we have found that a stable solution can be obtained despite the very narrow dynamic range of the half-precision format.We develop an implementation with the CUDA platform, which, on most recent graphics processing units (GPU), is nearly twice as fast and uses half the memory of the equivalent single-precision version. The error on seismograms caused by the reduced precision is shown to correspond to a negligible fraction of the total seismic energy and is mostly incoherent with seismic phases. Finally, we find that this noise does not adversely impact full-waveform inversion nor reverse time migration, which both benefit from the higher throughput of half-precision computation.

Destruction of a lava dome observed with photogrammetry, acoustic and seismic sensors at Volcán de Colima, Mexico

During the period December 2016 to March 2017 the lava dome emplaced in September–November 2016 at Volcán de Colima was partially destroyed by Vulcanian explosions. In particular, 10 moderate-large explosions were observed with heights of 2–6.8 km from the crater and with the generation of pyroclastic density currents (PDCs), shock waves and ballistics. The acoustic and seismic energies were calculated for each event. The values found are similar to other moderate-large Vulcanian explosions observed at other volcanoes, the maximum value of seismic energy was of 1.6 × 109 J and for acoustic energy 7.5 × 108 J. These values were compared with the height of the eruptive column, which resulted in a poor correlation. For the acoustic signals, the reduced pressure was greater than that commonly reported for Vulcanian explosions elsewhere. Using the time or arrival of the acoustic and seismic signals, the depth of the acoustic-seismic source was estimated at <310 m for nine explosions. With photogrammetry (SfM method), the volume lost during the excavation of a crater between 5 December and 12 March was estimated, the volume being 9.8 × 105 m3. The total seismic energy released during these dates was 5.7 × 109 J. With these data, a relation between the lost volume and the total seismic energy of 1.6 × 10−4 m3/J was obtained. With this relation, the volume destroyed due to future explosions could be estimated, if the seismic energy release is known.

BELARUS

The annual review of seismicity in the territory of Belarus based on the data of two analogs and eighteen digital stations is presented. Forty-three events with Кd=4.6–8.2 were recorded. These were attributed to the southern part of the territory, which includes the Soligorsk mining area. The map of epicenters of all the events and the table showing their distribution by months are presented. The N(K) function for 2013 was compared with those for 1983–2012. The amount of seismic energy released in 2013 is 1.89 times higher than in 2012 and 5.13 times lower than its average value for the previous 30 years. The distribution of the events according to their energy classes and total seismic energy by months in 2013 as well as for the period of 31 years from 1983 till 2013 was provided. The time history, time of day, and day of week distributions of seismicity recorded in 2013 are presented.

CARPATHIANS

The seismic observations in the Carpathian region in 2013, which were conducted, as before, by two organizations from two states: in Ukraine, by the seismicity department of the Carpathian region of the Institute of Geophysics of the National Academy of Sciences of Ukraine, and in Moldova by the seismology laboratory of the Institute of Geology and Seismology of the Academy of Sciences of Moldova are described. There were 19 digital stations with a processing center in Lviv, Ukraine, and 6 stations with a center in Chisinau, Moldova. Various programs, local hodographs, and magnitudes were used. The consolidated catalog of earthquakes is created in Lviv. The map of epicenters and the table of the distribution of earthquakes of differ-ent classes by regions are given. The total number of earthquakes in 2013 was N=98 in the range of КР=5.7–14.1 and the depth interval of hypocenters h=1–150 km with total seismic energy Е=1.331014 J. Of these, 19 earthquakes with depths h=80–160 km is located in the Vrancea zone. Two maximum earth-quakes with КР=14.1 and КР=12.3 were recorded on October 6 and 15 in the Vrancea mountains with h=139.8 and 140.9 km. In Forecarpathians and Transcarpathia all earthquakes are weaker. The most significant event in Transcarpathia was the earthquake on April 4, 2013, with КР=8.4 in the area of «Nizhnее Selishche» seismic station. The earthquake source is located in the earth's crust at a depth of h=1.7 km. The earthquake was felt by the population of the Village Nizhnее Selishche with an intensity I=3–4. In general, in all seismic active zones of the Carpathians in 2013, there was a slight increase in the level of seismicity compared with that in 2012.

TAJIKISTAN

The catalog of Tajikistan earthquakes for 2013 contains 4997 earthquakes with КР=8.6–15.0, of which 3865 are deep-focus Pamir-Hindu Kush earthquakes with h=70–250 km and 1132 – shallow earthquakes scattered throughout the territory. The total seismic energy released in the foci of all earthquakes amounted to Е=1.461015 Joules. Immediately within the borders of the Republic the largest perceptible (КР=12.4, Mw=4.7, I0=6) was the earthquake on November 10 in the Wakhdat region. The largest among deep earth-quakes in 2013 occurred in the Afghan subzone on April 4 with КР=14.0, Mw=5.4, h=250 km. Due to a big depth, it caused shocks of low intensity (I3) in the epicentral zone but was felt in Tajikistan, Afghanistan, Pakistan. However, in general, the seismic process in the Republic proceeded in the background regime.

Якутия

. The paper presents the results of monitoring seismicity in Yakutia in 2013 based on the data from 24 digital seismic stations. A total of 5197 seismic events with Кp=6–15 are detected. A map of earthquake epicenters is compiled showing their distribution in different areas. Two major clusters of seismic events are recognized. The first one corresponds to the Arctic-Asian seismic belt (AASB) extending across the Laptev Sea shelf and the north eastern Asian continent towards the Sea of Okhotsk. The second Baikal–Stanovoy belt in the south of the region is traced from Lake Baikal through the Stanovoy Highlands and the Stanovoy Ridge to the Sea of Okhotsk. In South Yakutia, the Olekma–Stanovoy zone (OSZ), which makes the eastern part of the belt, is considered. Both belts form boundaries of major lithospheric plates. The first belt separates the Eurasian and North American plates, while the other divides the Eurasian plate from the Amurian one. The minimum seismic level is recorded within the OCZ, with no more than 0.04 % of the total seismic energy re-leased during 2013. The maximum seismicity is noted in the AASB with released energy making up 99.9 % of the total amount. That abrupt change in seismicity is due to the occurrence here of three strong earth-quakes, Ulakhan-Chistay, Ilin-Tas (Abyi), and Tas-Khayakhtakh with the intensities VII-IX in the epicenters (MS=4.9–6.9). The epicentral zone of the Tas-Khayakhtakh event (MS=4.9) that occurred on May, 2013 is considered in more detail. The motion in the source of this event indicate thrusting along the Dogdo fault. All the shakes took place within the Chersky Range, in the zone of influence of major faults of the Kolyma–Indigirka system (Ulakhan, Dogdo, Ilin–Tas) under conditions of NE compression (regime of interplate collision and transpression ). Seismotectonic relations, macroseismic data, and earthquake focal mechanism pa-rameters are discussed.

ALTAI and SAYAN MOUNTAINS

The review of the Altai-Sayan region seismicity for 2013 is presented. The permanent seismic network included 41 stations. In addition, there were 4 local temporary networks in operation during the year with 55 stations in total. There were 11548 earthquakes recorded with the total seismic energy of 1.81·1015 J. The most significant earthquakes in 2013 occurred in the area of the Bachatsky coal mine on June 18 and in the Altai Republic on January 24, both with ML=6.1. A brief description of the seismicity of the Chui-Kurai zone of the Altai Mountains is given.

Ongoing mass wasting processes in the Traful lake area, Argentinean Patagonia

The Patagonian Andes are characterized by a high relief, with numerous confined lakes in deep glacial valleys that currently experience minor rock falls. Although, there is a poorly known historical and post-glacial register of mass wasting phenomena and a complete absence of monitoring for potential future processes. In particular, the area called Los lagos, in Argentina, which is located south of latitude 35° S, where the glacial erosion shaped several valleys on both sides of the Andean range. The Andean area between 35° and 42° S has been releasing almost 25% of the world's total seismic energy from the adjacent subduction zone. The objective of this work is to analyze, a sector, in the northern margin of the Traful Lake, called Bosque Sumergido. The name of Bosque Sumergido was given because of the presence of an area of submerged dead trees in life position where part of the wood can be found underwater. In this work, we evaluate the potential risk for the city of Traful, located in front of it. We described this area in the context of mass wasting processes, the coastal morphological changes that occurred in the last 22 years and even some underwater features and bathymetry and analyzed the potential risk of tsunamis due to material falling into Traful Lake.