scholarly journals Spatio-Temporal Evolution of Intermediate-Depth Seismicity Beneath the Himalayas: Implications for Metamorphism and Tectonics

2021 ◽  
Vol 9 ◽  
Author(s):  
Konstantinos Michailos ◽  
N. Seth Carpenter ◽  
György Hetényi
Keyword(s):  
Fault Zone ◽  
Earthquake Catalog ◽  
Waveform Data ◽  
Central Himalayas ◽  
Intermediate Depth ◽  
Migration Rates ◽  
Spatio Temporal ◽  
Tear Fault ◽  
Dehydration Processes ◽  
The Himalaya

Intermediate-depth earthquakes (>40 km) have been observed beneath the central Himalayas over decades, with little known about their nature and characteristics. Here, we apply a state-of-the-art systematic processing routine, starting from continuous waveform data, to obtain the most comprehensive high-quality earthquake catalog with a focus on the intermediate-depth seismicity beneath the central Himalayas. We construct a catalog containing 414 robust earthquake locations with depths ranging from 40 to 110 km spanning from late 2001 till mid-2003. We calculate earthquake magnitudes in a consistent way and obtain values ranging between ML 0.8 and 4.5 with a magnitude of completeness of Mc 2.4. This information allows us to study the spatiotemporal characteristics of the seismicity in great detail. Earthquakes mainly take place in a cluster, consisting of two linear segments at ca. 35° azimuth difference, situated beneath the high Himalayas in NE Nepal and adjacent S. Tibet. Seismicity there does not feature any mainshock-aftershock patterns but presents a few sequences with potential seismicity migration rates compatible with linear or diffusive migration. This result, along with previous studies in the lower Indian crust, allows interpreting these events as related to metamorphic reactions involving dehydration processes. However, given the geodynamic context, a tectonic interpretation with a dextral basement fault zone propagating beneath the Himalaya and continuing as a westward propagating tear fault would also be possible. This represents a continuous fault zone from the deep crust in S. Tibet, across the Himalaya along the Dhubri-Chungthang fault zone (DCFZ) to the Shillong plateau, which could be an inherited tectonic feature.

scholarly journals A HOMOGENEOUS EARTHQUAKE CATALOG OF INTERMEDIATE-DEEP FOCUS GLOBAL SEISMICITY: COMPLETENESS AND SPATIO-TEMPORAL ANALYSIS

2017 ◽  
Vol 50 (3) ◽  
pp. 1270
Author(s):  
A.D. Tsampas ◽  
E.M. Scordilis ◽  
C.B. Papazachos ◽  
G.F. Karakaisis
Keyword(s):  
Large Scale ◽  
Spatiotemporal Analysis ◽  
Temporal Analysis ◽  
Mean Value ◽  
Earthquake Catalog ◽  
Intermediate Depth ◽  
Spatio Temporal ◽  
Global Seismicity ◽  
Deep Focus ◽  
The Moment

homogeneous with respect to magnitude earthquake catalog is compiled, particularly focusing on the global intermediate depth-deep focus seismicity and by exploiting data of almost half-century. Within a two-step compilation process, we take advantage of 10 robust conversion equations produced exclusively for intermediate depth and deep focal data (Tsampas et al., 2016). Initially, magnitudes of different scales and several origins are converted into proxy moment magnitudes (Mw*~Mw) and a weighted mean-value aggregation procedure is then applied for all events with estimated Mw*. Therefore, a homogeneous magnitude scale (equivalent to Mw) is obtained as result of individual correlations between different magnitude scales and the moment magnitude (Mw) scale, yielding a unique magnitude value per event. Moreover, through implementing a simple optimization scheme, a composed, unique depth value per event is estimated, utilizing focal data from multiple resources. In the end and after validating magnitude’s (M) reliability, a brief spatiotemporal analysis of the provided catalog is performed, revealing its potential for further exploitation in large scale seismological surveys or other research studies of global interest.

scholarly journals Evaluation of crustal inhomogeneity parameters in the southern Longmenshan fault zone and adjacent regions

2020 ◽  
Vol 24 (6) ◽  
pp. 1175-1188
Author(s):  
Xiao-Ping Fan ◽  
Yi-Cheng He ◽  
Cong-Jie Yang ◽  
Jun-Fei Wang
Keyword(s):  
Fault Zone ◽  
Lower Crust ◽  
Tectonic Deformation ◽  
Upper Crust ◽  
Crust And Upper Mantle ◽  
Study Region ◽  
Waveform Data ◽  
Longmenshan Fault Zone ◽  
Deformation Features ◽  
Longmenshan Fault

AbstractBroadband teleseismic waveform data from 13 earthquakes recorded by 70 digital seismic stations were selected to evaluate the inhomogeneity parameters of the crustal medium in the southern Longmenshan fault zone and its adjacent regions using the teleseismic fluctuation wavefield method. Results show that a strong inhomogeneity exists beneath the study region, which can be divided into three blocks according to its structure and tectonic deformation features. These are known as the Sichuan-Qinghai Block, the Sichuan-Yunnan Block, and the Mid-Sichuan Block. The velocity fluctuation ratios of the three blocks are approximately 5.1%, 3.6%, and 5.1% in the upper crust and 5.1%, 3.8%, and 4.9% in the lower crust. The inhomogeneity correlation lengths of the three blocks are about 10.1 km, 14.0 km, and 10.7 km in the upper crust and 11.8 km, 17.0 km, and 11.8 km in the lower crust. The differences in the crustal medium inhomogeneity beneath the Sichuan-Yunnan Block, the Sichuan-Qinghai Block, and the Mid-Sichuan Block may be related to intensive tectonic movement and material flow in the crust and upper mantle.

Tracking earthquake sequences in real time: application of Seismicity-Scanning based on Navigated Automatic Phase-picking (S-SNAP) to the 2019 Ridgecrest, California sequence

2020 ◽  
Vol 223 (3) ◽  
pp. 1511-1524
Author(s):  
Fengzhou Tan ◽  
Honn Kao ◽  
Edwin Nissen ◽  
Ryan Visser
Keyword(s):  
Real Time ◽  
Fault Zone ◽  
Southern California ◽  
Main Shock ◽  
Waveform Data ◽  
Major Earthquake ◽  
Automatic Phase ◽  
Seismicity Monitoring ◽  
Earthquake Sequences ◽  
Automatic Phase Picking

SUMMARY Recent improvements in seismic data processing techniques have enhanced our ability to detail the evolution of major earthquake sequences in space and time. One such advance is new scanning algorithms that allow large volumes of waveform data to be analysed automatically, removing human biases and inefficiencies that inhibit standardized monitoring. The Seismicity-Scanning based on Navigated Automatic Phase-picking (S-SNAP) workflow has previously been shown to be capable of producing high-quality earthquake catalogues for injection-induced seismicity monitoring. In this study, we modify the original S-SNAP workflow to enable it to delineate the spatiotemporal distribution of major earthquake sequences in real time. We apply it to the 2019 Ridgecrest, southern California earthquake sequence, which culminated in an Mw 6.4 foreshock on July 4 and an Mw 7.1 main shock on July 6 and generated tens of thousands of smaller earthquakes. Our catalogue—which spans the period 2019 June 1 to July 16—details the spatiotemporal evolution of the sequence, including early foreshocks on July 1 and accelerating foreshocks on July 4, a seismicity gap before the main shock around its epicentre, seismicity on discrete structures within a broad fault zone and triggered earthquakes outside the main fault zone. We estimate the accuracy and false detection rate of the S-SNAP catalogue based on the reviewed catalogue reported by Southern California Seismic Network (SCSN) and our own visual inspection. We demonstrate the advantages of S-SNAP over a generalized automatic earthquake monitoring software, Seiscomp3, and a customized real-time earthquake information system for southern California, TriNet. In comparison, the S-SNAP catalogue contains five times more events than the Seiscomp3 catalogue and 1.4–2.2 times as many events per hour as the TriNet catalogue at most times. In addition, S-SNAP is more likely to solve phase association ambiguities correctly and provide a catalogue with consistent quality through time. S-SNAP would be beneficial to both routine network operations and the earthquake review process.

Stochastic Strong Ground Motion Simulation of the Southern Aegean Sea Benioff Zone Intermediate‐Depth Earthquakes

2018 ◽  
Vol 108 (2) ◽  
pp. 946-965 ◽  
Author(s):  
Ch. Kkallas ◽  
C. B. Papazachos ◽  
B. N. Margaris ◽  
D. Boore ◽  
Ch. Ventouzi ◽  
...  
Keyword(s):  
Aegean Sea ◽  
Benioff Zone ◽  
Model Parameters ◽  
Waveform Data ◽  
Intermediate Depth ◽  
Stress Parameter ◽  
Finite Fault ◽  
Strong Ground Motion Simulation ◽  
Back Arc ◽  
Parameter Values

Abstract We employ the stochastic finite‐fault modeling approach of Motazedian and Atkinson (2005), as adapted by Boore (2009), for the simulation of Fourier amplitude spectra (FAS) of intermediate‐depth earthquakes in the southern Aegean Sea subduction (southern Greece). To calibrate the necessary model parameters of the stochastic finite‐fault method, we used waveform data from both acceleration and broadband‐velocity sensor instruments for intermediate‐depth earthquakes (depths ∼45–140  km) with M 4.5–6.7 that occurred along the southern Aegean Sea Wadati–Benioff zone. The anelastic attenuation parameters employed for the simulations were adapted from recent studies, suggesting large back‐arc to fore‐arc attenuation differences. High‐frequency spectral slopes (kappa values) were constrained from the analysis of a large number of earthquakes from the high‐density EGELADOS (Exploring the Geodynamics of Subducted Lithosphere Using an Amphibian Deployment of Seismographs) temporary network. Because of the lack of site‐specific information, generic site amplification functions available for the Aegean Sea region were adopted. Using the previous source, path, and site‐effect constraints, we solved for the stress‐parameter values by a trial‐and‐error approach, in an attempt to fit the FAS of the available intermediate‐depth earthquake waveforms. Despite the fact that most source, path, and site model parameters are based on independent studies and a single source parameter (stress parameter) is optimized, an excellent comparison between observations and simulations is found for both peak ground acceleration (PGA) and peak ground velocity (PGV), as well as for FAS values. The final stress‐parameter values increase with moment magnitude, reaching large values (>300  bars) for events M≥6.0. Blind tests for an event not used for the model calibration verify the good agreement of the simulated and observed ground motions for both back‐arc and along‐arc stations. The results suggest that the employed approach can be efficiently used for the modeling of large historical intermediate‐depth earthquakes, as well as for seismic hazard assessment for similar intermediate‐depth events in the southern Aegean Sea area.

scholarly journals Statistical behaviours of earthquake occurrences in the Central Anatolian Region of Turkey: region-time-magnitude analyses

Baltica ◽  
2021 ◽  
pp. 157-173
Author(s):  
Serkan Öztürk
Keyword(s):  
Fault Zone ◽  
Earthquake Hazard ◽  
B Value ◽  
Short Term ◽  
Small Magnitude ◽  
Strong Earthquakes ◽  
Recurrence Times ◽  
Z Value ◽  
Spatio Temporal

The main objective of this work is to make detailed region-time-magnitude analyses by describing the statistical behaviours of earthquakes in the Central Anatolian Region of Turkey. In this scope, several seismic and tectonic parameters such as Mcomp, b-value, Dc-value, Z-value, recurrence times and annual probabilities were evaluated. For the analyses, a homogeneous catalogue including 10,146 earthquakes with 1.0 ≤ Md ≤ 5.7 between 30 July 1975 and 29 December 2018 was used and spatio-temporal changes of earthquake behaviours were mapped for the beginning of 2019. Earthquake magnitudes varied from 1.9 to 3.0 on average, and hence Mcomp was considered to be 2.6. The b-value was calculated as 1.26 ± 0.07, and this relatively large value indicates that small-magnitude events are dominant. The Dc-value was computed as 1.31 ± 0.03. This small value means that distances between epicentres approach the diameter of the cluster, and seismic activity is more clustered at smaller scales or in larger regions. The spatio-temporal analyses of recurrence times suggest that the Central Anatolian Region has an intermediate/long-term earthquake hazard in comparison to occurrences of strong earthquakes in the short term. Several anomaly regions of a small b-value and a large Z-value were found in and around the Tuzgölü Fault Zone, Central Anatolian Fault Zone, Salanda fault and Niğde fault at the beginning of 2019. Thus, a combination of the regions with a lower b-value, a higher Z-value and also moderate recurrence times may give significant clues for the future possible earthquakes, and detected regions may be thought to be the most likely areas for strong/large events in the Central Anatolian Region.

Seismicity and tectonics of western Venezuela

1972 ◽  
Vol 62 (6) ◽  
pp. 1711-1751 ◽  
Author(s):  
James W. Dewey
Keyword(s):  
Fault Zone ◽  
South American ◽  
Seismic Zone ◽  
South American Plate ◽  
Intermediate Depth ◽  
Hypocenter Determination ◽  
Joint Hypocenter Determination ◽  
Shallow Earthquakes ◽  
Seismicity And Tectonics ◽  
North And South

abstract New seismicity data on western Venezuela and northeastern Colombia are presented. Teleseismically recorded earthquakes from 1930 through 1970 have been relocated by Joint Hypocenter Determination (JHD) or with source-station adjustments calculated by JHD. Additionally, 540 days of recording have been obtained with local seismographs installed near the Boconó Fault. The most intense shallow activity occurred north and south of the Tachira Depression along the eastern flank of the Cordillera Oriental of Colombia. The Boconó Fault Zone is seismically active; small shallow shocks were recorded in it by the local stations. Shallow earthquakes also occur in the Cordillera de Mérida away from the Boconó Fault. The new hypocenters for the intermediate-depth Bucaramanga earthquakes define a smaller source volume than defined by previously computed hypocenters. A previously inferred southward-dipping seismic zone near Bucaramanga is probably spurious, a consequence of correlation between errors in latitude and errors in depth. If one assumes that these intermediate-depth earthquakes lie on a single lithospheric slab, that slab strikes approximately north and dips to the east. The distribution of hypocenters and focal mechanisms support the platetectonic hypothesis that the present tectonics of northwestern Venezuela are a result of eastward motion of the Caribbean plate with respect to the South American plate. The principal interface between these two plates may have changed within the last 5 m.y. from a zone of underthrusting west of the Sierra de Perija to the predominantly right-lateral Boconó Fault Zone.

Is the quiescence of major earthquakes (M ≧ 7.5) Since 1952 in the Himalaya and northeast India real?

1996 ◽  
Vol 86 (6) ◽  
pp. 1983-1986
Author(s):  
S. P. Satyabala ◽  
Harsh K. Gupta
Keyword(s):  
Northeast India ◽  
Earthquake Catalog ◽  
Fold Belt ◽  
Magnitude Scales ◽  
The Himalaya

Abstract The earthquake catalog for the Himalaya and the northeast India regions (latitude 20°N to 38°N and longitude 75°E to 100°E, comprising of portions of the Himalaya and Arakan Yoma fold belt) for the period 1897 to May 1995 shows that there have been 14 major earthquakes (M ≧ 7.5) during the period 1897 to 1952 and no major earthquakes after 1952. To investigate the possibility that this quiescence is an artifact of nonuniform magnitude scales over the period of study, we examined three global catalogs and found that there is indeed an absence of major earthquakes after 1952.

Imaging the rupture process of recent earthquakes using backprojection of local high frequency records

2020 ◽  
Author(s):  
Ioannis Fountoulakis ◽  
Christos Evangelidis ◽  
Olga-Joan Ktenidou
Keyword(s):  
High Frequency ◽  
A Priori ◽  
Strong Motion ◽  
Seismic Hazard Assessment ◽  
Seismic Source ◽  
Site Effect ◽  
Source Inversion ◽  
Waveform Data ◽  
Novel Approach ◽  
Spatio Temporal

<p>The seismic source spatio-temporal rupture processes of events in Japan, Greece and Turkey are imaged by backprojection of strong-motion waveforms. Normalized high-frequency (> 2Hz) S-waveforms from recordings on dense strong-motion networks are used to scan a predefined 3D source volume over time. </p><p>Backprojection is an alternative novel approach to image the spatio-temporal earthquake rupture. The method was first applied for large earthquakes at teleseismic distances, but is nowadays also used at local distances and over higher frequencies. The greatest advantage of the method is that processing is done without any a-priori constraints on the geometry, or size of the source. Thus, the spatio-temporal imaging of the rupture is feasible at higher frequencies (> 1Hz) than conventional source inversion studies, even when the examined fault geometry is complex. This high-frequency energy emitted during an earthquake is of great importance in seismic hazard assessment for certain critical infrastructures. The actual challenge in using high-frequency local recordings is to distinguish the local site effects from the true earthquake source content - otherwise, mapping the former incorrectly onto the latter limits the resolvability of the method. It is not straightforward to remove the site effect component or even to distinguish good reference stations from amid hard-soil and rock sites. In this study, the advantages and limitations of the method are explored using waveform data from well-recorded events in Japan (Kumamoto Mw7.1, 2016), Turkey (Marmara Mw6.4, 2019) and Greece (Antikythera Mw6.1, 2019). For each event and seismic array the resolution limits of the applied method are explored by performing various synthetic tests.</p>

scholarly journals Active Faulting in Lake Constance (Austria, Germany, Switzerland) Unraveled by Multi-Vintage Reflection Seismic Data

2021 ◽  
Vol 9 ◽  
Author(s):  
S.C. Fabbri ◽  
C. Affentranger ◽  
S. Krastel ◽  
K. Lindhorst ◽  
M. Wessels ◽  
...  
Keyword(s):  
Fault Zone ◽  
Seismic Data ◽  
Single Channel ◽  
Fault Zones ◽  
Lake Constance ◽  
Earthquake Catalog ◽  
Tectonic Structures ◽  
Reflection Seismic ◽  
The North ◽  
Major Fault

Probabilistic seismic hazard assessments are primarily based on instrumentally recorded and historically documented earthquakes. For the northern part of the European Alpine Arc, slow crustal deformation results in low earthquake recurrence rates and brings up the necessity to extend our perspective beyond the existing earthquake catalog. The overdeepened basin of Lake Constance (Austria, Germany, and Switzerland), located within the North-Alpine Molasse Basin, is investigated as an ideal (neo-) tectonic archive. The lake is surrounded by major tectonic structures and constrained via the North Alpine Front in the South, the Jura fold-and-thrust belt in the West, and the Hegau-Lake Constance Graben System in the North. Several fault zones reach Lake Constance such as the St. Gallen Fault Zone, a reactivated basement-rooted normal fault, active during several phases from the Permo-Carboniferous to the Mesozoic. To extend the catalog of potentially active fault zones, we compiled an extensive 445 km of multi-channel reflection seismic data in 2017, complementing a moderate-size GI-airgun survey from 2016. The two datasets reveal the complete overdeepened Quaternary trough and its sedimentary infill and the upper part of the Miocene Molasse bedrock. They additionally complement existing seismic vintages that investigated the mass-transport deposit chronology and Mesozoic fault structures. The compilation of 2D seismic data allowed investigating the seismic stratigraphy of the Quaternary infill and its underlying bedrock of Lake Constance, shaped by multiple glaciations. The 2D seismic sections revealed 154 fault indications in the Obersee Basin and 39 fault indications in the Untersee Basin. Their interpretative linkage results in 23 and five major fault planes, respectively. One of the major fault planes, traceable to Cenozoic bedrock, is associated with a prominent offset of the lake bottom on the multibeam bathymetric map. Across this area, high-resolution single channel data was acquired and a transect of five short cores was retrieved displaying significant sediment thickness changes across the seismically mapped fault trace with a surface-rupture related turbidite, all indicating repeated activity of a likely seismogenic strike-slip fault with a normal faulting component. We interpret this fault as northward continuation of the St. Gallen Fault Zone, previously described onshore on 3D seismic data.

Sign in / Sign up

Export Citation Format

Share Document