Новые переходные соотношения для энергетических характеристик землетрясений Cахалинского региона

Two significant earthquakes of magnitude ML 4.6 and 4.5 occurred on 18 January and 3 December 2021 in the central region of the Yellow Sea, respectively. The earthquakes occurred beneath the Gunsan sedimentary basin at about 10 km depth with a strike-slip faulting mechanism on nodal planes striking northwest–southeast (NW–SE) and north-northeast–south-southwest (NNE–SSW). Despite a lack of close-by seismographic stations, we successfully utilized regional Lg-wave observations on both coasts of the sea—the Korean peninsula on the east and eastern China on the west. For nine earthquakes in two event sequences, the Lg-wave differential travel times of the nearby event pairs at the common station are carefully measured using the waveform cross-correlation technique. The double-difference earthquake relocation method is employed to obtain precise relative epicentral locations using the Lg correlation measurements. Relocated epicenters align along the NW–SE direction, indicating that the nodal plane striking the same direction is the likely fault plane on which both sequences occurred. This is the first case reported in the literature in which the causative fault plane has been identified for earthquakes in the central Yellow Sea region. It has an important implication for current regional tectonics; it favors neither old tectonic features trending NE–SW (Qianliyan uplift) nor the north–south alignment of significant earthquakes in the region along the Amur plate boundary. The Lg waves from the earthquake sequences are dominant seismic signals on all three-component records at stations in 160–550 km and allowed us to analyze source properties of the two largest earthquakes using the empirical Green’s function approach. Azimuthal variations of the source corner frequencies suggest that earthquake rupture likely propagated toward southeast (125°) along the fault plane, supporting the aftershock relocation results.

Relationship between shallow and deep seismicity in the western Pacific region

The question of the existence of foci of deep earthquakes in the region of the Crimea-Black Sea-Caucasus is extremely important from the point of view of the geodynamics of the region. Previously it was thought that only crustal earthquakes could occur in this region. Recently, results have been obtained that show that earthquakes with depths of at least 300 km occur in this region. The article discusses the question of how plausible these results are and why they were not obtained earlier. Seven specific examples of the ambiguous determination of the depth of earthquake hypocenters in the Crimea-Black Sea-Caucasus region are considered. These examples clearly show that determining the coordinates of earthquake hypocenters using algorithms based on the Geiger method does not allow one to uniquely determine the depth of the hypocenters. The article gives an idea of the authors about the origin of mantle earthquakes in the Caucasian and Crimean-Black Sea regions. For the Caucasus region, mantle earthquakes are associated with two reasons: submersion of the lithospheric layer; in the asthenospheric layer, represented in the seismotomographic sections by a low-velocity anomaly, the nature of earthquake foci is associated with fluids formed during phase transition reactions. In the Crimean-Black Sea region, earthquake foci are located in the lithosphere layer, and the sliding of the lithosphere along the less viscous underlying layer of the upper mantle causes tectonic movements in the lithosphere accompanied by earthquakes. In addition, to determine the coordinates of the hypocenters of the Crimean and Caucasian earthquakes during routine processing, hodographs were used for depths not exceeding 35 km for the Crimea and 50 km for the Caucasus and 150 for the North Caucasus. This circumstance is the main reason why deep earthquakes could not be detected.

Ground motion prediction equations (GMPE) in terms of macroseismic intensity are a prerequisite for intensity-based shake maps and seismic hazard assessment and have the advantage of direct relation to earthquake damage and good data availability also for historical events. In this study, we derive GMPE for macroseismic intensity for the Campania region in southern Italy. This region is highly exposed to the seismic hazard related to the high seismicity with moderate- to large-magnitude earthquakes in the Appenninic belt. The relations are based on physical considerations and are easy to implement for the user. The uncertainties in earthquake source parameters are accounted for through a Monte Carlo approach and results are compared to those obtained through a standard regression scheme. One relation takes into account the finite dimensions of the fault plane and describes the site intensity as a function of Joyner–Boore distance. Additionally, a relation describing the intensity as a function of epicentral distance is derived for implementation in cases where the dimensions of the fault plane are unknown. The relations are based on an extensive dataset of macroseismic intensities for large earthquakes in the Campania region and are valid in the magnitude range M w = 6.3–7.0 for shallow crustal earthquakes. Results indicate that the uncertainties in earthquake source parameters are negligible in comparison to the spread in the intensity data. The GMPE provide a good overall fit to historical earthquakes in the region and can provide the intensities for a future earthquake within 1 intensity unit.

Theoretical ray paths through velocity models constructed from numerically calculated thermal models of slabs were computed. The results were in good agreement with observed travel times. First motion amplitudes of P waves at teleseismic distances were measured from long- and short-period WWSSN records of intermediate focus earthquakes in the Tonga, Kermadec, and Kurile regions and of nuclear explosions and shallow earthquakes in the Aleutian region. These amplitudes were corrected for source mechanism. The Aleutian data were sufficient to show that intermediate focus earthquakes in that region occur in the colder regions of the slab. At short periods, for regions other than the Aleutians, shadowing effects which could be associated with the slab were not very marked, less than a factor of 2 reduction for epicentral distances between 30° and 50°. No systematic effects due to plates were found in the long-period data. Some stations in the predicted shadow zone of a Tonga earthquake recorded low amplitude precursors which probably were greatly defocused waves which ran the full length of the slab. Simple diffraction is incapable of explaining the short-period results.

Research Article| August 01, 1969 Focal Mechanisms of Deep and Shallow Earthquakes in the Tonga-Kermadec Region and the Tectonics of Island Arcs BRYAN ISACKS; BRYAN ISACKS Earth Sciences Laboratories, ESSA, Lamont Geological Observatory of Columbia University, Palisades, New York Search for other works by this author on: GSW Google Scholar LYNN R SYKES; LYNN R SYKES Lamont Geological Observatory of Columbia University, Palisades, New York Search for other works by this author on: GSW Google Scholar JACK OLIVER JACK OLIVER Lamont Geological Observatory of Columbia University, Palisades, New York Search for other works by this author on: GSW Google Scholar Author and Article Information BRYAN ISACKS Earth Sciences Laboratories, ESSA, Lamont Geological Observatory of Columbia University, Palisades, New York LYNN R SYKES Lamont Geological Observatory of Columbia University, Palisades, New York JACK OLIVER Lamont Geological Observatory of Columbia University, Palisades, New York Publisher: Geological Society of America Received: 24 Oct 1968 Revision Received: 23 Jan 1969 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1969, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1969) 80 (8): 1443–1470. https://doi.org/10.1130/0016-7606(1969)80[1443:FMODAS]2.0.CO;2 Article history Received: 24 Oct 1968 Revision Received: 23 Jan 1969 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation BRYAN ISACKS, LYNN R SYKES, JACK OLIVER; Focal Mechanisms of Deep and Shallow Earthquakes in the Tonga-Kermadec Region and the Tectonics of Island Arcs. GSA Bulletin 1969;; 80 (8): 1443–1470. doi: https://doi.org/10.1130/0016-7606(1969)80[1443:FMODAS]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Well-determined focal mechanisms based on reliable first motions of both compressional and shear waves are presented for 18 shallow, 6 intermediate, and 15 deep-focus earthquakes in the Fiji-Tonga-Kermadec region of the Southwest Pacific. The double-couple model is an adequate representation for earthquake mechanisms at all depths; most of the mechanisms are characterized by a predominance of dip-slip motions. The orientations of the mechanisms of deep and shallow earthquakes appear to be systematically and fundamentally different in respect to the orientation of the seismic zone. Whereas the shallow mechanisms all appear to accommodate movements between the adjacent sides of the seismic zone, the slip planes of the deep earthquake mechanisms are systematically nonparallel to the deep seismic zone. Hence, the deep zone of activity does not appear to be a simple thrust fault. The P, B, and T axes of the double-couple solutions tend to parallel the dip, strike, and normal directions, respectively, of the portions of the Tonga seismic zone deeper than about 80 km. The P axes tend to be more stable in orientation than the B and T axes. Large variations in the orientations of some of the deep mechanisms may reflect contortions of the deep seismic zone in a simple geometrical fashion. The shallow mechanisms indicate that thrust faulting is occurring beneath the inner (islandward) margins of the Tonga and Kermadec Trenches and that transform faulting is occurring at the northern end of the Tonga Arc. The over-all interpretation of the shallow mechanisms also includes hinge faulting south of Samoa at the juncture of the thrust and transform faults.These results, which are also in agreement with mechanism data for other regions such as Japan where both numerous and reliable data are available, are most simply interpreted by a tectonic model of an island arc in which (a) shallow earthquakes occur between a segment of lithosphere that moves downward into the mantle and the segments of lithosphere on the surface, and (b) deep earthquakes occur within the downgoing slab in response to a compressional stress within it. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

A moderate earthquake of magnitude ML 5.3 occurred in the Yellow Sea on January 12, 2011. We estimated the source parameters and found that the quake was a shallow strike-slip fault event with a moment magnitude of 4.6. The stress drop of this event, 1.2–2.0 MPa, is lower than that of moderate earthquakes inland and at the eastern offshore of the Korean Peninsula, and also that of the typical value for shallow intraplate earthquakes. A stronger event (M ∼ 6) in the southern Yellow Sea in 1984 was previously reported to have a low stress drop. Therefore the low stress drop is probably characteristic of earthquakes in the Yellow Sea region. We found that aftershocks of the 2011 Yellow Sea event, with magnitudes greater than 2, occurred for about 5 days, while similar-sized aftershocks of some inland earthquakes of the Korean Peninsula continued for several hours only. The lower stress drop and greater active aftershocks in the Yellow Sea region might reflect a different tectonic setting from that on the Korean Peninsula.

Shallow and intermediate depth earthquakes in the Hindu Kush region across the Afghan-Pakistan border

The paper presents a review of the seismicity of the southern part of the Russian Far East in 2022 based on the data from the catalog of the “Yuzhno-Sakhalinsk” Regional Information Processing Center of the Sakhalin Branch of the Federal Research Center "United Geophysical Survey of the Russian Academy of Sciences". The main parameters of the seismicity, such as the statistical estimation of seismicity level SESL'09, Benioff diagrams, density maps of conditional elastic deformation in 2022 compared to the previous longer time interval, are estimated. A brief analysis of the most significant and interesting earthquakes for detailed study is given. The seismicity of the Kuril-Okhotsk, Sakhalin and the Amur and Primorye regions in 2022 remained within the background values. At the same time, seismic activation was noted in the Sakhalin region, manifested in a number of moderately strong events on the northeastern shelf, in the Uglegorsky district, north of the Schmidt Peninsula, as well as a strong mantle event in the La Perouse Strait with Mw = 5.9. The strongest earthquake of the Kuril-Okhotsk region with Mw = 6.0 occurred in the southern part of the Kuril Island arc. A long series of moderately strong events in the Middle Kurils with Mw up to 5.6 attracts attention. The problem of operational processing of earthquakes in the Amur region and Primorye due to the decreasing number of seismic stations in this region is noted, as well as the systematic underestimation of the energy characteristics of deep-focus earthquakes.

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.

— This paper reviews some remarkable characteristics of earthquakes in a Stable Continental Region (SCR) of the South China Block (SCB). The kernel of the SCB is the Yangtze platform solidified in late Proterozoic time, with continental growth to the southeast by a series of fold belts in Paleozoic time. The facts that the deviatoric stress is low, the orientations of the major tectonic features in the SCB are substantially normal to the maximum horizontal principal stress, and a relatively uniform crust, seem to be the major reasons for lack of significant seismicity in most regions of the SCB. Earthquakes in this region are mainly associated with three seismic zones: (1) the Southeast China Coast seismic zone related to Guangdong-Fujian coastal folding belt (associated with Eurasia-Philippine Sea plate collision); (2) the Southern Yellow Sea seismic zone associated with continental shelf rifts and basins; and (3) the Downstream Yangtze River seismic zone spatially coinciding with Tertiary rifts and basin development. All three seismic zones are close to one or two major economic and population centers in the SCB so that they pose significant seismic hazards. Earthquake focal mechanisms in the SCB are consistent with strike-slip to normal faulting stress regimes. Because of the global and national economic significance of the SCB and its dense population, the seismic hazard of the region is of outstanding importance. Comparing the SCB with another less developed region, a pending earthquake with the same size and tectonic setting would cause substantially more severe social and economic losses in the SCB. This paper also compiles an inventory of historic moderate to great earthquakes in the SCB; most of the data are not widely available in English literature.

Damaging earthquakes in Australia and other regions characterised by low seismicity are considered low probability but high consequence events. Uncertainties in modelling earthquake occurrence rates and ground motions for damaging earthquakes in these regions pose unique challenges to forecasting seismic hazard, including the use of this information as a reliable benchmark to improve seismic safety within our communities. Key challenges for assessing seismic hazards in these regions are explored, including: the completeness and continuity of earthquake catalogues; the identification and characterisation of neotectonic faults; the difficulties in characterising earthquake ground motions; the uncertainties in earthquake source modelling, and; the use of modern earthquake hazard information to support the development of future building provisions. Geoscience Australia recently released its 2018 National Seismic Hazard Assessment (NSHA18). Results from the NSHA18 indicate significantly lower seismic hazard across almost all Australian localities at the 1/500 annual exceedance probability level relative to the factors adopted for the current Australian Standard AS1170.4–2007 (R2018). These new hazard estimates have challenged notions of seismic hazard in Australia in terms of the recurrence of damaging ground motions. This raises the question of whether current practices in probabilistic seismic hazard analysis (PSHA) deliver the outcomes required to protect communities and infrastructure assets in low-seismicity regions, such as Australia. This manuscript explores a range of measures that could be undertaken to update and modernise the Australian earthquake loading standard, in the context of these modern seismic hazard estimates, including the use of alternate ground-motion exceedance probabilities for assigning seismic demands for ordinary-use structures. The estimation of seismic hazard at any location is an uncertain science, particularly in low-seismicity regions. However, as our knowledge of the physical characteristics of earthquakes improve, our estimates of the hazard will converge more closely to the actual – but unknowable – (time independent) hazard. Understanding the uncertainties in the estimation of seismic hazard is also of key importance, and new software and approaches allow hazard modellers to better understand and quantify this uncertainty. It is therefore prudent to regularly update the estimates of the seismic demands in our building codes using the best available evidence-based methods and models.

—There is accumulating evidence that distributed seismicity is a problem in statistical physics. Seismicity is taken to be a type example of self-organized criticality. This association has important implications regarding earthquake hazard assessment and forecasting. A characteristic of a thermodynamic system is that it exhibits a background noise that is self-organized. In the case of a dilute gas, this self-organization is the Maxwell–Boltzmann distribution of molecular velocities. In seismicity, it is the Gutenberg–Richter frequency-magnitude scaling; this scaling is fractal. Observations favor the hypothesis that smaller earthquakes in moderate-sized regions occur at rates that are only weakly dependent on time. Thus, the rate of occurrence of smaller earthquakes can be extrapolated to assess the hazard of larger earthquakes in a region. We obtain the rate of occurrence of earthquakes with m > 4 in 1°× 1° areas from the NEIC catalog. Using only this data we produce global maps of the seismic hazard. Observations also favor the hypothesis that the stress level at which an earthquake occurs is a second-order critical point. As a critical point is approached, correlations extend over increasingly larger distances. In terms of seismicity, the approach to a critical point is associated with an increase in the rate of occurrence of intermediate-sized earthquakes prior to a large earthquake. This precursory activation has been shown to exhibit power-law scaling and to occur over a region about ten times larger than the rupture length of the large earthquake. Analyses of the spinoidal behavior associated with second-order critical points predict the power-law increase in seismic activity prior to a characteristic earthquake. This precursory activation provides the basis for intermediate-range earthquake forecasting.

The localization of epicenters and the intensity of local earthquakes in the Chernivtsi region were studied. It has been established that low-energy earthquakes can create a local dangerous level of shaking in its north-eastern part. The seismic danger of the territory of Chernivtsi region is usually identified with the manifestations of earthquakes in the epicentral zone of the Vrancea Mountains. In this, the most seismically active part of the Carpathians, deep-focus earthquakes with stable localization of foci occur. The Vrancea seismic body can be considered as a zone that is in a constant mode of preparation for a strong earthquake, while the earth's crust above the strip of deep-focus hypocenters is practically seismic. The highest, so far registered, intensity of earthquakes in the Chernivtsi region earthquakes of the Vrancea zone is 7, the predicted maximum is estimated at 8 points on the MSK-64 scale. At the same time, the danger of local earthquakes was considered insignificant, and the study of the peculiarities and intensity of their manifestation was of little relevance. The aim of the study is to analyze the location of epicenters and assess the intensity of local tectonic earthquakes in the Chernivtsi region. Components of seismic hazard of any area are the manifestations of local earthquakes and the impact of seismic shocks, the epicenters of which are outside it. Chernivtsi region is not characterized by high local seismic activity, but so far, several local earthquakes with an intensity in the epicenter of 4-5 points have been registered in its territory. A rather strong earthquake was felt in Chernivtsi on May 10, 1950 at 2 o'clock. 10 min (Greenwich). The duration of his three jolts, which took place in the vertical direction, did not exceed 2-3 seconds. During the earthquake, doors opened, dishes rang in closets, and window glass shattered in some rooms. The intensity of the earthquake GV Brusentsov scored 5 points. The most notable seismic event, the shocks of which were felt in the northwest of Chernivtsi region, was the earthquake that occurred on January 20, 1903 at 3 o'clock. 4 min (Greenwich). Intensity in the epicenter, located near the village. Dobrovlyany (Ternopil region), rated 6 points on the MSK scale. At this intensity, the magnitude of the earthquake, the focus of which was at a depth of 10-15 km, was about 4.5. In the territories of Kelmenetsky and, especially, Sokyryansky districts, earthquakes are felt, the epicenters of which are located in the south of Khmelnytsky and Vinnytsia regions. Several earthquakes were registered in the same area, which were felt in the city of Novodnistrovsk with an intensity of 3-4 points. Their occurrence is associated with disturbance of geodynamic balance in the near-surface part of the earth's crust, caused by filling the bowl of the Dniester reservoir. The epicenters of the earthquakes were located 15-20 km east of the Dniester HPP dam. The magnitude in the case of the strongest shocks was 3.5-3.8, their intensity near the epicenter - 5 points. The estimated depth of the hearth was 5 km. An important feature of these energetically weak earthquakes was the small (2-5 km) depth of the focus. Under such conditions, at magnitudes of 2.8–3.8, a high (5.5–7.3 points) level of shaking was observed in the epicenter, but the intensity decreased rapidly with increasing epicentral distance. Evidence of the possibility of a seismic event of considerable intensity in the northeast of Chernivtsi region may be the presence of paleoseismic dislocations in this area. In particular, such a geological and geomorphological complex located on the Dniester canyon near the village. Mosquitoes, described in the work of B. Ridush and Y. Kalush. The reason for the formation of the Komariv paleoseismic dislocation may be the manifestation of a local tectonic earthquake. The territory of Chernivtsi region is not characterized by high seismic activity. The intensity of local energetically weak (with M≤4.5) earthquakes did not exceed 5-6 points of the MSK scale. When the hypocenters were found at shallow depths within the earth's crust, a marked level of shaking was observed in the epicenters, which rapidly decreased with increasing epicentral distance. The epicenters of the earthquakes were located along the lines of tectonic faults of the south-western edge of the Eastern European platform and the Pre-Carpathian marginal depression. The danger for the regional center of Chernivtsi in 5-6 points can be created by the intensification of Chernivtsi or Storozhynets tectonic faults, the last of which was marked by an earthquake in 1950. More intense (5-7) points may be local manifestations of earthquakes in the south-eastern part of the region, in particular, near the city of Novodnistrovsk. The seismic activity of tectonic processes within the mountainous, north-western part of the region needs to be studied.

Crustal Q in Southern Italy determined from regional earthquakes