Deep Earthquakes Research Articles

Cosmic Expansion: The Dynamic Force Source for All Planetary Tectonic Movements

In this paper, the relationship between the geodynamics and cosmic expansion is analyzed and demonstrated from the basic physical principles and various natural phenomena, and the conclusion is drawn that cosmic expansion is the dynamic force source of all planetary tectonic movements in the universe. The energy for the formation and change of landscape and the energy of earthquakes and volcanic eruptions all come from the cosmic expansion. With the cosmic expansion, the energy density of space is decreasing, the atoms and molecules of all matter in the universe are growing, and the magma is expanding and producing gases. As the earth’s internal pressure rises, the mechanical energy that accumulates within the magma forms the driving force of the earth’s various tectonic movements, and the release of these energy and matter (expansive magma and high-pressure gases) leads to the formation and the changes of the landform (such as orogenesis, epeirogenesis, the formation of the earth’s plates, the Earth expansion, the seafloor spreading, and the continental drift), as well as to earthquakes and volcanic eruptions. In this paper, the causes of all kinds of earthquakes, especially deep focus earthquakes, are given and almost all known seismic phenomena are explained, the basic principle and method of earthquake prediction are given, and the direction is pointed out for the elimination of earthquakes and the utilization of earthquake energy. Based on the same principle of physics, this paper also shows that the Ice-Age is caused by the acceleration of the speed of the motion of the solar system relative to the Milky Way in certain regions of the Milky Way. The greater the speed of the solar system relative to the Milky Way, the greater the drop in Earth surface temperature.

Deep Structure and Folded-Block Structure of the Garhwal Himalayas (India): Results of Integrated Geological and Geophysical Study

The geological and geophysical study of the representative segment of the Alpine-Himalayan mobile belt—the Central zone of the Garhwal Himalaya—was conducted. The results of structural and geological studies in conjunction with the data on the deep structure obtained by geophysical methods, compared the speed of horizontal movements and the position of the hypocenters of seismic events, are presented. The successive decrease in the current rates of transverse compression is observed as we approach the maximum topographical heights of the geological and geophysical profile stretching across the Garhwal Himalaya. The large fault zones are shown, to which are related the foci of deep earthquakes.

Unusually deep earthquakes in the central Sierra Nevada (California, USA): Foundering ultramafic lithosphere?

AbstractUsing a network of temporarily deployed broadband seismometers, we characterize an unusual region of crustal earthquakes in the west-central Sierra Nevada, California (USA). We locate 131 earthquakes, which occurred from 3.1 to 47.1 km deep during June 2005 to May 2006. We detect more events, at greater depths, than are present in the Northern California Seismic Network catalog during this period. Most of the events occur at depths of 20–35 km and cluster into two distinct groups. In addition, some of the events appear to be repeating due to the similarity of their waveforms and locations. We calculate focal mechanisms for 52 of these events, and about half exhibit reverse faulting, which represents a state of horizontal compressional stress that is distinct from the regional stress field. From first arrivals, we calculate a one-dimensional model of crustal P-wavespeeds, which resolves a gradational increase from 5.8 km/s near the surface to 6.7 km/s at 35 km depth. The events overlie a significant variation in the character of the Moho, and two long-period events occur near the seismically imaged Moho at nearly 40 km depth. We suggest that these earthquakes could be the seismogenic response of the crust to active foundering of mafic-ultramafic lithosphere and resultant asthenospheric upwelling beneath the central Sierra Nevada.

Evidence of ridge propagation in the eastern Gulf of Mexico from integrated analysis of potential fields and seismic data

Integrated analysis of gravity, magnetic, and seismic data reveals two phases of spreading in the eastern Gulf of Mexico (GOM) including two distinct spreading centers, suggesting a major ridge reorganization during the opening of the eastern part of the GOM. Ridge propagation between the two spreading episodes explains the following observations: 1) the drastic asymmetry in the oceanic domain of northeastern GOM, 2) the presence of two distinct crustal zones with dramatically different thickness and physical properties, and 3) the observed seismicity within the oceanic domain that is not aligned with any known tectonic structure. The initial Late Jurassic spreading center (~160 Ma) resulted in thin (~5 km) and uniform oceanic crust with a fast compressional velocity (7 km/s). Based on our analysis, the estimated full spreading rate of this older spreading event is less than 1 cm/yr. The spreading regime changed in Early Cretaceous around 150 Ma, resulting in a propagation (i.e., jump) of the spreading center. The new spreading episode was characterized by a change in spreading direction and increased magma supply as it produced thicker (up to 9 km) oceanic crust with a typical two-layered structure. Despite the increase in magmatic material, the full rate of this younger spreading event estimated from our analysis is only slightly faster (1.1 cm/yr assuming that spreading ceased at 137 Ma). The later conclusion is consistent with the morphology of the spreading centers mapped by seismic data. Our analysis shows that recent deep crustal earthquakes in the middle of the Gulf of Mexico are aligned with the boundary between the two identified distinct oceanic zones, referred here as a pseudofault.

The 2018 Fiji Mw 8.2 and 7.9 deep earthquakes: One doublet in two slabs

The cold Fiji-Tonga subduction zone accounts for >75% of cataloged deep earthquakes but none of the largest ten in the last century. On 19 August 2018 and 06 September 2018, a deep earthquake doublet with moment magnitude (Mw) 8.2 and 7.9 struck the Fiji area, providing a rare opportunity to interrogate the behaviors of great deep earthquakes in cold slabs. While the aftershock productivity of the 2018 Mw 8.2 event is similar to the 2013 Okhotsk Mw 8.3 event in a cold slab, the inferred compact rupture dimensions of both the Mw 8.2 and 7.9 events appear to be similar to the 1994 Bolivia earthquake in a warm slab. This seems to contradict the traditional view that slab temperature controls deep earthquakes. However, we find that neither event was confined within the cold Tonga slab core: the Mw 8.2 ruptured mostly in the warmer rim of the Tonga slab and the Mw 7.9 occurred in a warm relic slab leaning on top of the Tonga slab. The Fiji doublet demonstrates local slab temperature as the critical factor for deep earthquakes, and reveals complex interaction of subducted slabs in Tonga.

Migration of shallow and deep slow earthquakes toward the locked segment of the Nankai megathrust

The Nankai megathrust is located offshore Shikoku and Kyushu, Japan and is characterized by various kinds of slow earthquakes whose relative motions across the plate boundary faults are slower than regular earthquakes. In the area, the interplate locking is stronger in the northern area (offshore Shikoku) than in the southern area (offshore Kyushu) and Mw ∼8 earthquakes (Nankai earthquakes) have occurred repeatedly in the northern area. In this paper, the spatio-temporal distributions of slow earthquakes (very low frequency earthquakes, tremors and slow-slip events) are examined based on the analyses of repeating earthquakes and slow earthquakes with special focus on the interaction between different activities. A comprehensive analysis of the seismic and geodetic data from 2003 to 2016 indicates complementary distribution of various types of slow earthquakes down to 35–50 km depth outside the Nankai main locking area. We also found interactions between different kinds of activities. The interactions between the repeating earthquakes and slow earthquakes suggest that the area of the repeating earthquakes activity can be divided into deeper (depth ≥ 20 km) and shallower (depth < 20 km) areas. The analyses of deep repeating earthquakes and the inland Global Navigation Satellite System (GNSS) data suggests slow northward migrations of long-term slow slip events (SSEs) in 20–50 km (offshore Kyushu) and 20–35 km (under Shikoku) depths along the plate boundary. These migrations occurred during a period of 2–3 years that includes the 2003 and 2010 large slow-slip events in the Bungo channel located in between Kyushu and Shikoku. The analysis has also shown interaction between shallow repeating earthquakes and shallow very low frequency earthquakes which indicates faster northward migrations of short-term SSEs from the shallow plate boundary offshore Kyushu to the deeper area under Shikoku over the duration of a month during the 2010 long-term slow-slip episode. The deep slow migration and the shallow to deep fast migration of SSEs in a ∼300 km area towards and around the source area of the recurrent Nankai earthquake (Mw 8.0–8.6) indicates the occurrence of a widespread non-steady stress build-up process around the source area of the Nankai megathrust earthquake.

Distributed sensing of microseisms and teleseisms with submarine dark fibers

Sparse seismic instrumentation in the oceans limits our understanding of deep Earth dynamics and submarine earthquakes. Distributed acoustic sensing (DAS), an emerging technology that converts optical fiber to seismic sensors, allows us to leverage pre-existing submarine telecommunication cables for seismic monitoring. Here we report observations of microseism, local surface gravity waves, and a teleseismic earthquake along a 4192-sensor ocean-bottom DAS array offshore Belgium. We observe in-situ how opposing groups of ocean surface gravity waves generate double-frequency seismic Scholte waves, as described by the Longuet-Higgins theory of microseism generation. We also extract P- and S-wave phases from the 2018-08-19 {M}_{w}8.2 Fiji deep earthquake in the 0.01-1 Hz frequency band, though waveform fidelity is low at high frequencies. These results suggest significant potential of DAS in next-generation submarine seismic networks.

Geodynamic processes preceding to deep Okhotomorsky earthquake May 24, 2013 with magnitude MW = 8,3

The set of parameters of geophysical fields and geodynamic events before the strongest Okhotsk Sea earthquake May 24, 2013 with MW = 8,3 and a focal depth of 630 km in this paper analyzed. In the temporary vicinity of the earthquake (May 19-20), there was a temporary synchronization of geodynamic processes in areas of the Kamchatka Peninsula, separated by hundreds of kilometers. The simultaneous occurrence of anomalies in the behavior of tilts, in the dynamics of flow of subsoil radon, conditional deformations of remote foreshock activation in Avacha Bay, speaks of a single geodynamic process on a regional scale, preceding the earthquake. A possible reason for the observed in-phase geodynamic phenomena may be the geodeformation wave that arose at the last stage of the preparation of the Okhotsk Sea earthquake.

A Strong Seismic Reflector within the Mantle Wedge above the Ryukyu Subduction of Northern Taiwan

AbstractMajor structures within the mantle wedge are often revealed from seismic velocity anomalies, such as low‐velocity zones at magma reservoirs, partial melting regions, or the upwelling asthenosphere. However, no significant seismic boundaries have been reported in the shallow mantle wedge beneath volcanic arcs. Here, we present evidence for a strong seismic reflector dipping in the opposite direction of the subducting slab in the mantle wedge beneath northern Taiwan in the western end of the Ryukyu subduction system. We find that two unambiguous P waves generated by a deep earthquake (ML 5.1) at a depth of 132.5 km were clearly recorded by the dense seismic array (Formosa Array), composed of 140 broadband seismic stations with a station spacing of approximately 5 km in northern Taiwan. Forward modeling using both raytracing and travel times shows that a seismic reflector exists beneath the Tatun volcano group (TVG) around depths of 80–110 km. The reflector dips in the opposite direction of the subducting slab and is unlikely to be associated with mantle wedge corner flow. Instead, it probably belonged to parts of possible structures such as the asthenospheric flow, the mantle diapir, or other undiscovered structures above the subducting slab. No matter what the seismic boundary is exactly, it might be associated with the active volcanism in the TVG. The detailed geometry and mechanism of the seismic boundary in the mantle wedge will be obtained as the Formosa Array collects more seismic data in the near future.

Сахалин

The review of seismicity for Sakhalin in 2013 based on the data of four seismic stationary stations and 10 temporary digital seismic stations "DAT", working in the south of Sakhalin, is given. The main parameters of 688 earthquakes and focal mechanisms of five of them are determined. 42 earthquakes showed a macroseismic effect. The maps of the representativeness of earthquakes and of epicenters are given, the distribution of crust and deep earthquakes on the magnitude and their summarized energy for seven seismoactive districts are presented. For each area, seismic conditions are described. The seismicity of the Sakhalin region in 2013 can be characterized as moderate. Somewhat increased seismic activity was recorded in the East Sakhalin region, against the background seismicity in previous years. Somewhat increased activity was also recorded in the West Sakhalin region, where a moderately strong earthquake occurred with MLH=5.1.

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.

Камчатка и Командорские острова

The seismicity of Kamchatka and surrounding territories for 2013 is viewed. The minimum local magnitude of completeness is MLmin=3.25 in the Kamchatka earthquake catalogue totally, and MLmin=4 for earthquakes under the Okhotsk sea (with h≥350 km). The Kamchatka earthquake catalogue of 2013 with ML≥3.6, which includes 1750 events, is published. 146 earthquakes of published catalog with ML=3.6–7.8 were felt with seismic intensity ranged from 2 to 7 of the MSK-64 scale in Kamchatka and surrounding areas. Focal mechanisms were determined in two ways: 1) from first motion P-wave arrivals for 107 earthquakes; 2) using waveforms for 25 earthquakes. The background seismicity level (SESL’09) within the Kamchatka responsibility zone was extremely high in 2013. It exceeded the rate of seismicity in all previous years of observations. There were 6672 earthquakes, including 129 events with КS≥11.5 (ML≥5) in the region during the year. The mechanisms of 107 earthquakes were defined. 148 earthquakes were felt with intensity from 2 up to 7 on the territory of Kamchatskii Krai, North Kuril Islands, and Komandor Islands. There were several unusual events in 2013. The strong earthquake with magnitude Mw=5.8 on March 13 in the area of the Kamchatka Isthmus (Il'pyr earthquake), which is a rare phenomenon for the Northern Kamchatka. There was the strongest deep earthquake in the world (Mw=8.3) on May 24 under the Sea of Okhotsk (Okhotsk earthquake) at the depth of 630 km. The event caused an abnormal macro-seismic effect. The intensive earthquake swarm was observed in the Avacha Bay (Mwmax=6.1) in May 2013. It is the strongest earthquake swarm registered by the Kamchatka network during the period of detailed seismological observations since 1962

ОХОТОМОРСКОЕ-III ЗЕМЛЕТРЯСЕНИЕ 24 мая 2013 г. с Mwрег=8.3, I0=6 (Охотскоеморе)

The strongest deep earthquake on May 24, 2013 (Mwreg=8.3) is discussed. It occurred under the Sea of Okhotsk at a depth of about 630 km. The instrumental hypocenter location reported by the KB GS RAS is φ=54.75N, λ=153.78E, h=630 km. Three magnitudes were obtained: local magnitude ML=7.8, code-wave magnitude Mc=7.6, moment magnitude Mwreg=8.3. The Okhotsk earthquake hypocenter is located on the northern part of the ancient slab, practically at the lower end of the seismogenic region. The earthquake caused significant co-seismic displacements at most GNSS observation points. The earthquake focal mecha-nisms solutions have been obtained by three ways. The solutions are very similar. The submeridial hollow falling nodal plane seems more preferable. For the deep quake of May 24, 2013, a series of aftershocks were registered. The aftershock process had three consistent stages with different decay character. The cloud of deep-focus aftershocks has the 400200 km size, with the 450–700 km depth range and is extended in the North–South direction. The aftershock process has the three-phase character and can be considered as a stream of seismic events decreasing in time with three successive stages with different attenuation modes. The change in attenuation modes is associated with strong aftershocks. The duration of the decaying after-shock process is ~ 280 days. The anomalous distribution of impact was observed for the earthquake: 1) a large range of macroseismic effect – quake was felt throughout the World; 2) in the territory of Kamchatka, maximum shakes and ground motions were observed at the points located on the eastern coast of Kamchat-ka, and at comparable northern and western distances macroseismic and instrumental intensities were lower. Despite the globality of the macroseismic effect, in the nearest settlements (Kamchatka region), the earth-quake was felt with intensity up to 5–6 and caused no damage. The May 24, 2013 earthquake produced many strong motion records. The ground motion characteristics such as peak amplitudes of motion, spectral shape and response spectrum were received using the records of the earthquake from Kamchatka network of digital accelerographs.

Deep Earthquakes in the Caucasus: Recalculation Results

The question of the existence of deep earthquake sources in the Caucasus is extremely important both for solving geodynamics problems, assessing seismic hazard, and seismic zoning of the region. It was previously believed that earthquakes with depths not exceeding 150 km can occur in the Caucasus. However, in recent years, this has become argumentative, reflected in a number of publications. This article shows that in the Caucasus, in addition to crustal earthquakes, rather deep mantle earthquakes also occur. This, in addition to direct determinations, is confirmed by data published in Caucasian earthquake catalogs and bulletins. The presence of deep earthquake sources in the Caucasus significantly changes our views on the regional structure and geotectonics. Obviously, crustal earthquakes dominate in the region’s seismicity, but it is clear that mantle earthquakes also make a significant contribution. The fact that they are fewer than crustal earthquakes in the total number may indicate that the crust is harder and more brittle than the upper mantle. Keywords: earthquakes, hypocenters, catalogs, bulletins

Evaluation of the Solar Radiation in a Seismic Zone

The solar radiation affects the life on Earth and it is important in meteorology, climatology, solar energy, agriculture, hydrology and seismology, too. The Sun warms the earth which reflects a part of the energy. An effect of tectonic stress increases the ground temperature that is radiated into the atmosphere. We study the possibility to use the variation of reflected energy in correlation with seismicity, radon concentration, CO2 emission, ULF radio waves, telluric currents, air ionization, temperature in borehole and acoustic noise. In this case, the solar radiation is a precursor factor. This research is important to study the effects of climate change. Analyzing the solar energy budget we find information about the atmosphere: aerosols, ozone, sulfur dioxide, carbon dioxide, nitrogen dioxide and pollution. Our multidisciplinary network (AeroSolSys) monitors Vrancea, a Romanian area characterized by deep earthquakes. For this study, we use two stations, Plostina and Vrancioaia, where we have a net radiometer and a pyranometer. The first sensor includes two pyranometers (up and low) and two pyrgeometers (up and low), a Pt-100 and a Thermistor. The spectral range covers both the Solar Radiation, 0.3 to 3 micrometers, and the Far Infrared Radiation, 4.5 to 42 micrometers. In this case, we measure and determine the temperature of sensor necessary for pyrgeometers, pyranometer short-wave radiation up and low EyU - EyL, pyrgeometers long-wave radiation up and low EgU - EgL, Albedo, net solar radiation NSR, net far infrared radiation NFIR, net total radiation NTR, sky temperature SkyT and, land surface temperature LST. In Vrancioaia, we have a pyranometer with range 0.3 – 2.8 micrometers and maxim 1600 W/m2. Two video cameras monitor the sky and the measurements are correlated with meteorological equipment installed in each location. We use information about solar activity from NOAA satellites and Copernicus CAMS. The humidity of ground is important in energy budget and it is estimated from meteorological data and telluric currents. The interval of analysis is 3 hours, between 2016.01.01 – 2018.05.31. It is difficult to notice the effect of tectonic stress since the daily and seasonal variations of solar radiation are high but global warming is obvious. Solar radiation monitoring helps us to understand other phenomena like radon emission or air ionization.

Geodynamic Processes Preceding the Sea of Okhotsk Deep Earthquake of May 24, 2013, with Magnitude Mw = 8.3

Geodynamic Processes Preceding the Sea of Okhotsk Deep Earthquake of May 24, 2013, with Magnitude Mw = 8.3

The 30 November 2018 Mw 7.1 Anchorage Earthquake

AbstractThe Mw 7.1 47 km deep earthquake that occurred on 30 November 2018 had deep societal impacts across southcentral Alaska and exhibited phenomena of broad scientific interest. We document observations that point to future directions of research and hazard mitigation. The rupture mechanism, aftershocks, and deformation of the mainshock are consistent with extension inside the Pacific plate near the down‐dip limit of flat‐slab subduction. Peak ground motions &amp;gt;25%g were observed across more than 8000 km2, though the most violent near‐fault shaking was avoided because the hypocenter was nearly 50 km below the surface. The ground motions show substantial variation, highlighting the influence of regional geology and near‐surface soil conditions. Aftershock activity was vigorous with roughly 300 felt events in the first six months, including two dozen aftershocks exceeding M 4.5. Broad subsidence of up to 5 cm across the region is consistent with the rupture mechanism. The passage of seismic waves and possibly the coseismic subsidence mobilized ground waters, resulting in temporary increases in stream flow. Although there were many failures of natural slopes and soils, the shaking was insufficient to reactivate many of the failures observed during the 1964 M 9.2 earthquake. This is explained by the much shorter duration of shaking as well as the lower amplitude long‐period motions in 2018. The majority of observed soil failures were in anthropogenically placed fill soils. Structural damage is attributed to both the failure of these emplaced soils as well as to the ground motion, which shows some spatial correlation to damage. However, the paucity of instrumental ground‐motion recordings outside of downtown Anchorage makes these comparisons challenging. The earthquake demonstrated the challenge of issuing tsunami warnings in complex coastal geographies and highlights the need for a targeted tsunami hazard evaluation of the region. The event also demonstrates the challenge of estimating the probabilistic hazard posed by intraslab earthquakes.

Experimental evidence for wall-rock pulverization during dynamic rupture at ultra-high pressure conditions

The mechanisms triggering intermediate and deep earthquakes have puzzled geologists for several decades. There is still no consensus concerning whether such earthquakes are triggered by brittle or ductile mechanisms. We performed a deformation experiment on a synthetic lawsonite-bearing blueschist at a confining pressure of 3 GPa and temperatures from 583 to 1,073 K. After deformation, the recovered sample reveals conjugated shear fractures. Garnet crystals are dissected and displaced along these narrow faults and reveal micro- and nanostructures that resemble natural pulverization structures as well as partial amorphization. Formation of such structures at low confining pressures is known to require high tensile stresses and strain rates and is explained by the propagation of a dynamic shear rupture. The absence of shearing in the pulverized wall rock is taken as evidence that these structures pre-date the subsequent heat-producing frictional slip. In analogy to observations at low pressure we infer that the garnet structures in our experiment result from rapid propagation of a shear fracture even at the high pressure exerted on the sample and thus suggest that brittle deformation is possible at lower crustal to upper mantle depths.

Mantle earthquakes beneath Fogo volcano, Cape Verde: Evidence for subcrustal fracturing induced by magmatic injection

Fogo volcano belongs to the Cape Verde hotspot and its most recent eruption occurred from November 2014 to February 2015. From January to December 2016 we operated a temporary seismic network and array on Fogo and were able to locate 289 earthquakes in total. Array analysis shows that most of the events occur within the crust at distances >25km near the neighboring island of Brava. However, on 15th August 2016 the network recorded an isolated cluster of >20 earthquakes, 13 of which could be located beneath the southern part of Fogo. The differences between S- and P-wave arrival times at steep incidence clearly indicate focal depths between approximately 38 and 44km whereas receiver-function analyses place the Moho discontinuity at depths between 11 and 14km. Thus, the earthquakes are located well within the upper mantle directly beneath Fogo. In view of the elevated upper-mantle temperatures within a hotspot regime, we propose that fracturing induced by magmatic injection is the most likely cause for the observed deep earthquakes.

Anomalous SmKS induced by postcritical reflection and refraction at the core-mantle boundary

Earth’s outer core is generally thought to be a well-mixed liquid consisting mostly of iron and a small amount of lighter elements. Recent seismic studies using SmKS waves show that the top a few hundred kilometers of the outer core possess a P-wave velocity slightly lower than the PREM model, which cannot be explained by self-compression of a chemically homogeneous outer core. We investigated the SmKS waveforms of a deep earthquake occurring beneath South America recorded by a large and dense seismic array in China, and measured the differential arrival times of the SmKS pairs. We found significant waveform distortion of the SmKS caused by postcritical refraction and reflection at the core-mantle boundary. This waveform distortion can introduce significant bias to the measured differential times, leading to incorrect estimate of P-wave velocity of the outer core. Whether stable stratification is occurring in outer core or not requires further seismic investigations.