Precise Locating of the Great 1897 Shillong Plateau Earthquake Using Teleseismic and Regional Seismic Phase Data

Shiba Subedi; György Hetényi

doi:10.1785/0320210031

Precise Locating of the Great 1897 Shillong Plateau Earthquake Using Teleseismic and Regional Seismic Phase Data

The Seismic Record ◽

10.1785/0320210031 ◽

2021 ◽

Vol 1 (3) ◽

pp. 135-144

Author(s):

Shiba Subedi ◽

György Hetényi

Keyword(s):

Seismic Waves ◽

Active Faults ◽

Eastern Himalaya ◽

Great Earthquake ◽

Shillong Plateau ◽

Time Data ◽

Origin Time ◽

Velocity Models ◽

Rupture Plane ◽

Phase Data

Abstract Pinched between the Eastern Himalaya and the Indo-Burman ranges, the Shillong Plateau represents a zone of distributed deformation with numerous visible and buried active faults. In 1897, a great (magnitude 8+) earthquake occurred in the area, and although a subsurface rupture plane has been proposed geodetically, its epicenter remained uncertain. We gathered original arrival time data of seismic waves from this early-instrumental era and combined them with modern, 3D velocity models to constrain the origin time and epicenter of this event, including uncertainties. Our results show that the earthquake has taken place in the northwest part of the plateau, at the junction of the short, surface-rupturing Chedrang fault and the buried Oldham fault (26.0°N, 90.7°E). This latter fault has been proposed earlier based on geodetic data and is long enough to host a great earthquake. Rupture has most likely propagated eastward. Stress change from the 1897 earthquake may have ultimately triggered the 1930 M 7.1 Dhubri earthquake, along a fault connecting the Shillong Plateau with the Himalaya.

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Deterministic versus probabilistic seismic hazard assessment for the Shillong Plateau

10.5194/egusphere-egu2020-3834 ◽

2020 ◽

Author(s):

Alik Ismail-Zadeh ◽

Olympa Baro ◽

Abhishek Kumar

Keyword(s):

Seismic Hazard ◽

Hazard Assessment ◽

Active Faults ◽

Seismic Hazard Assessment ◽

Great Earthquake ◽

Lower Probability ◽

Shillong Plateau ◽

The West ◽

Probability Of Occurrence ◽

Garo Hills

<p>The Shillong Plateau is an earthquake-prone region in the northeastern India. Based on regional seismotectonic studies, we present the results of seismic hazard assessment, both deterministic (DSHA) and probabilistic (PSHA), and map peak horizontal accelerations (PHA) for three largely populated districts within the Shillong Plateau - the East Khasi hills, the Ri-Bhoi, and the West Garo hills. The hazard analysis methodology is based on the analysis of 72 earthquake sources (active faults) located within 500 km seismotectonic region around the plateau. Using an average sample log-likelihood approach, suitable ground motion prediction equations (GMPEs) are identified. As a variation in hypocentral distances can affect the ranks (or weights) of selected GMPEs, DSHA is performed separately for the three selected districts. DSHA shows that the northern part of the East Khasi hills, eastern part of Ri-Bhoi district and the West Garo hills districts exhibit the highest PHA value. DSHA indicates that the Barapani, Oldham, and Dauki faults influence significantly the seismic hazard of the studied region. In the case of PSHA, the annual frequency of exceedance of ground motions for three populated cities (Shillong city, Nongpoh, and Tura), located within above three districts respectively, are determined. Individual hazard curves indicate that the Barapani fault possesses the highest frequency of seismic hazard for Shillong city and Nongpoh. At Tura, both Eocene hinge zone and Dauki faults are responsible for the highest frequency of seismic hazard. The results of the PSHA are compared with those obtained using the DSHA approach indicating a difference between the two approaches for the West Garo hills district. It is shown that this difference is associated with the Oldham fault located near the district. The fault can produce a great earthquake, although with a lower probability of occurrence compared to a few other faults capable of producing smaller events with higher probability of occurrence. Hence, in the PSHA, the effect of the Oldham fault is less pronounced in terms of the design life of a structure, than in the case of the DSHA.</p>

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Structure of the central Sumatran subduction zone revealed by local earthquake travel-time tomography using an amphibious network

Solid Earth ◽

10.5194/se-9-1035-2018 ◽

2018 ◽

Vol 9 (4) ◽

pp. 1035-1049 ◽

Cited By ~ 5

Author(s):

Dietrich Lange ◽

Frederik Tilmann ◽

Tim Henstock ◽

Andreas Rietbrock ◽

Danny Natawidjaja ◽

...

Keyword(s):

Travel Time ◽

Subduction Zone ◽

Large Scale ◽

Sedimentary Basins ◽

Great Earthquake ◽

Ocean Bottom ◽

Time Data ◽

Plate Interface ◽

Seismicity Pattern ◽

Velocity Models

Abstract. The Sumatran subduction zone exhibits strong seismic and tsunamogenic potential with the prominent examples of the 2004, 2005 and 2007 earthquakes. Here, we invert travel-time data of local earthquakes for vp and vp∕vs velocity models of the central Sumatran forearc. Data were acquired by an amphibious seismometer network consisting of 52 land stations and 10 ocean-bottom seismometers located on a segment of the Sumatran subduction zone that had not ruptured in a great earthquake since 1797 but witnessed recent ruptures to the north in 2005 (Nias earthquake, Mw = 8.7) and to the south in 2007 (Bengkulu earthquake, Mw = 8.5). The 2-D and 3-D vp velocity anomalies reveal the downgoing slab and the sedimentary basins. Although the seismicity pattern in the study area appears to be strongly influenced by the obliquely subducting Investigator Fracture Zone to at least 200 km depth, the 3-D velocity model shows prevailing trench-parallel structures at depths of the plate interface. The tomographic model suggests a thinned crust below the basin east of the forearc islands (Nias, Pulau Batu, Siberut) at ∼ 180 km distance to the trench. vp velocities beneath the magmatic arc and the Sumatran fault zone (SFZ) are around 5 km s−1 at 10 km depth and the vp∕vs ratios in the uppermost 10 km are low, indicating the presence of felsic lithologies typical for continental crust. We find moderately elevated vp∕vs values of 1.85 at ∼ 150 km distance to the trench in the region of the Mentawai Fault. vp∕vs ratios suggest an absence of large-scale alteration of the mantle wedge and might explain why the seismogenic plate interface (observed as a locked zone from geodetic data) extends below the continental forearc Moho in Sumatra. Reduced vp velocities beneath the forearc basin covering the region between the Mentawai Islands and the Sumatra mainland possibly reflect a reduced thickness of the overriding crust.

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Location and source parameters of the 19 June 1994 (MW = 5.0) offshore Petrolia, California, earthquake

Bulletin of the Seismological Society of America ◽

10.1785/bssa0870010272 ◽

1997 ◽

Vol 87 (1) ◽

pp. 272-276

Author(s):

Jochen Braunmiller ◽

Beate Leitner ◽

John Nábělek ◽

Anne M. Tréhu

Keyword(s):

Moment Tensor ◽

Source Parameters ◽

Low Frequency ◽

P Wave ◽

Ocean Bottom ◽

Time Data ◽

Origin Time ◽

Depth Estimate ◽

Moment Tensor Solution ◽

Velocity Models

Abstract The MW = 5.0, 19 June 1994 offshore Petrolia, California, earthquake was well recorded by nine ocean-bottom hydrophones (OBH) and seismometers (OBS), providing an opportunity to precisely locate an earthquake in the tectonically active Mendocino triple junction region. Adding the offshore data improves the azimuthal station coverage and essentially removes the epicenter's sensitivity to the choice of inversion parameters and velocity models. The hypocentral parameters, assuming an oceanic upper-mantle velocity of 7.9 km/sec, are 10:39:33.2 UTC for origin time, 40.376° N latitude, 124.441° W longitude, and a depth of 18.8 km. The moment-tensor solution obtained by modeling of low-frequency regional waveforms indicates predominantly strike-slip faulting with a north-south-trending P axis, as is typical for Gorda plate earthquakes, and confirms the depth estimate from the P-wave travel-time data.

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Structure of the Central Sumatran Subduction Zone Revealed by Local Earthquake Travel Time Tomography Using Amphibious Data

10.5194/se-2017-128 ◽

2018 ◽

Author(s):

Dietrich Lange ◽

Frederik Tilmann ◽

Tim Henstock ◽

Andreas Rietbrock ◽

Danny Natawidjaja ◽

...

Keyword(s):

Travel Time ◽

Subduction Zone ◽

Large Scale ◽

Sedimentary Basins ◽

Great Earthquake ◽

Ocean Bottom ◽

Time Data ◽

Plate Interface ◽

Velocity Models ◽

3D Velocity Model

Abstract. The Sumatran subduction zone exhibits strong seismic and tsunamogenic potential with the prominent examples of the 2004, 2005 and 2007 earthquakes. Here, we invert travel time data of local earthquakes for vp and vp/vs velocity models of the central Sumatran forearc. Data were acquired by an amphibious seismometer network consisting of 52 land stations and 10 ocean bottom seismometers located on a segment of the Sumatran subduction zone that had not ruptured in a great earthquake since 1797 but witnessed recent ruptures to the north in 2005 (Nias earthquake, Mw = 8.7) and to the south in 2007 (Bengkulu earthquake, Mw = 8.5). 2D and 3D vp velocity anomalies reveal the downgoing slab and the sedimentary basins. Although the seismicity pattern in the study area appears to be strongly influenced by the obliquely subducting Investigator Fracture Zone to at least 200 km depth, the 3D velocity model shows prevailing trench parallel structures at depths of the plate interface. The tomographic model suggests a thinned crust below the basin east of the forearc islands (Nias, Pulau Batu, Siberut) at ~ 180 km distance to the trench. Vp velocities beneath the magmatic arc and the Sumatran fault zone SFZ are around 5 km/s at 10 km depth and the vp/vs ratios in the uppermost 10 km are low, indicating the presence of felsic lithologies typical for continental crust. We find moderately elevated vp/vs values of 1.85 at ~ 150 km distance to the trench in the region of the Mentawai fault. Vp/vs ratios suggest absence of large scale alteration of the mantle wedge and might explain why the seismogenic plate interface (observed as a locked zone from geodetic data) extends below the continental forearc Moho in Sumatra. Reduced vp velocities beneath the forearc basin covering the region between Mentawai Islands and the Sumatra mainland possibly reflect a reduced thickness of the overriding crust.

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Loma Prieta aftershock relocation with S-P travel times: Effects of 3-D structure and true error estimates

Bulletin of the Seismological Society of America ◽

10.1785/bssa0810051705 ◽

1991 ◽

Vol 81 (5) ◽

pp. 1705-1725

Author(s):

Susan Y. Schwartz ◽

Glenn D. Nelson

Keyword(s):

Arrival Time ◽

Velocity Structure ◽

P Wave ◽

S Wave ◽

Time Data ◽

Arrival Times ◽

Velocity Models ◽

Earthquake Locations ◽

Phase Data ◽

Loma Prieta

Abstract Aftershocks of the 18 October 1989 Loma Prieta, California, earthquake are located using S-P arrival-time measurements from stations of the PASSCAL aftershock deployment. We demonstrate the effectiveness of using S-P arrival-time data in locating earthquakes recorded by a sparse three-component network. Events are located using the program QUAKE3D (Nelson and Vidale, 1990) with both 2-D and 3-D velocity models that have been developed independently for this region. The dense coverage of the area around the Loma Prieta rupture zone by instruments of the California Network (CALNET) has allowed the U.S. Geological Survey (USGS) to find P-wave earthquake locations for both velocity models, which we compare with our solutions. We also perform synthetic calculations to estimate realistic location errors resulting from uncertainties in both the 3-D velocity structure and the timing of arrivals. These calculations provide a comparison of location accuracies obtained using S-P arrival times, S and P arrival times, and P times alone. We estimate average absolute errors in epicentral location and in depth for the Loma Prieta aftershocks to be just under 2 km and 1 km, respectively, using S-P phase data and the sparse PASSCAL instrument coverage. The synthetic tests show that these errors are much smaller than those predicted using P-wave data alone and are nearly the same as those predicted using S- and P-phase data separately. This suggests that future aftershock recording deployments with sparse networks of three-component data can retrieve accurate event locations even if absolute timing is problematic. We find moderate differences between our locations and those determined by the USGS from a larger network of stations; however, common characteristics in both seismicity patterns are apparent. Neither set of locations yields earthquake patterns that can be easily interpreted in terms of simple faulting geometries. The absence of a simple pattern in both sets of earthquake locations indicates that this complexity is not the result of earthquake mislocation but is a genuine feature of the seismicity. A deep southwesterly dipping plane and a near-vertical fault extending from the surface to at least 7-km depth beneath the surface trace of the San Andreas Fault are imaged by both sets of earthquake locations. Although earthquake locations indicate the existence of many more fault segments, the complexity of this region requires that a definitive picture of the faulting geometry will have to await improvement in our knowledge of the P- and S-wave velocity structures.

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Lithospheric structure models applied for locating the Romanian seismic events

Annals of Geophysics ◽

10.4401/ag-4215 ◽

1994 ◽

Vol 37 (3) ◽

Author(s):

M. Rizescu ◽

E. Popescu ◽

V. Oancea ◽

D. Enescu

Keyword(s):

Constant Velocity ◽

Seismic Waves ◽

Seismic Events ◽

Lithospheric Structure ◽

Structural Units ◽

Data Set ◽

Velocity Models ◽

Seismic Sequences ◽

Geological Information ◽

Propagation Velocities

The paper presents our attempts made for improving the locations obtained for local seismic events, using refined lithospheric structure models. The location program (based on Geiger method) supposes a known model. The program is run for some seismic sequences which occurred in different regions, on the Romanian territory, using for each of the sequences three velocity models: 1) 7 layers of constant velocity of seismic waves, as an average structure of the lithosphere for the whole territory; 2) site dependent structure (below each station), based on geophysical and geological information on the crust; 3) curves deseribing the dependence of propagation velocities with depth in the lithosphere, characterizing the 7 structural units delineated on the Romanian territory. The results obtained using the different velocity models are compared. Station corrections are computed for each data set. Finally, the locations determined for some quarry blasts are compared with the real ones.

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Seismicity, gravity, and tectonics of northeast India and northern Burma

Bulletin of the Seismological Society of America ◽

10.1785/bssa0660051683 ◽

1976 ◽

Vol 66 (5) ◽

pp. 1683-1694

Author(s):

R. K. Verma ◽

Manoj Mukhopadhyay ◽

M. S. Ahluwalia

Keyword(s):

Large Scale ◽

Bouguer Anomaly ◽

Northeast India ◽

Eastern Himalaya ◽

Basic Material ◽

Bengal Basin ◽

Seismic Zone ◽

Shillong Plateau ◽

Eurasian Plate ◽

High Seismicity

abstract Practically the whole of northeastern India and northern Burma is characterized as an anomalous gravity field as well as an area of high seismicity. The Bouguer anomaly in the region varies from +44 mgals over Shillong Plateau to −255 mgals near North Lakhimpur in Assam Valley. Isostatic anomaly (Hayford) varies from +100 to −130 mgals in these areas. Over Arakan-Yoma and the Burmese plains, the isostatic anomalies vary from −20 mgals to −100 mgals. Regions of high seismicity in the area include the eastern Himalaya (including Assam syntaxis), Arakan-Yoma including the folded belt of Tripura, Irrawaddy basin, Shillong Plateau, Dauki fault and the northern part of Bengal basin. The abnormal gravity and seismicity are related to large scale tectonic movements that have taken place in the area mostly during the Cretaceous and Cenozoic times, due to interaction of the Indian, Tibetan, and Burmese plates. The high seismicity indicates that the movements are continuing. The seismic zone underlying Burma is approximately V shaped and dips toward the east underneath Arakan-Yoma. Most of the intermediate-focus earthquakes in Burma underlie the area characterized by negative isostatic anomalies, indicating the probable existence of a subduction zone underneath the Arakan-Yoma and the Burmese plains. The Shillong Plateau has a history of vertical uplift since Cretaceous times. Provided this statement is true, the uplift of the plateau preceded Himalayan tectonics starting 20 to 30 m.y. before continental India made solid contact with the Eurasian plate. The plateau is characterized by large positive isostatic anomalies as well as high seismicity. The positive isostatic anomalies may be due to intrusion or incorporation of basic material from the mantle into the crust underlying the Plateau. These intrusions may have taken place through deep seated faults such as the Dauki and could be responsible for its uplift as well.

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Passive seismic event estimation using multiscattering waveform inversion

Geophysics ◽

10.1190/geo2018-0358.1 ◽

2019 ◽

Vol 84 (3) ◽

pp. KS59-KS69 ◽

Cited By ~ 8

Author(s):

Chao Song ◽

Zedong Wu ◽

Tariq Alkhalifah

Keyword(s):

Seismic Data ◽

Waveform Inversion ◽

Velocity Model ◽

Source Image ◽

Time Inversion ◽

Multiple Sources ◽

Origin Time ◽

Secondary Sources ◽

Velocity Models ◽

Passive Seismic

Passive seismic monitoring has become an effective method to understand underground processes. Time-reversal-based methods are often used to locate passive seismic events directly. However, these kinds of methods are strongly dependent on the accuracy of the velocity model. Full-waveform inversion (FWI) has been used on passive seismic data to invert the velocity model and source image, simultaneously. However, waveform inversion of passive seismic data uses mainly the transmission energy, which results in poor illumination and low resolution. We developed a waveform inversion using multiscattered energy for passive seismic to extract more information from the data than conventional FWI. Using transmission wavepath information from single- and double-scattering, computed from a predicted scatterer field acting as secondary sources, our method provides better illumination of the velocity model than conventional FWI. Using a new objective function, we optimized the source image and velocity model, including multiscattered energy, simultaneously. Because we conducted our method in the frequency domain with a complex source function including spatial and wavelet information, we mitigate the uncertainties of the source wavelet and source origin time. Inversion results from the Marmousi model indicate that by taking advantage of multiscattered energy and starting from a reasonably acceptable frequency (a single source at 3 Hz and multiple sources at 5 Hz), our method yields better inverted velocity models and source images compared with conventional FWI.

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Indication of active Faults in the New Madrid Seismic Zone from Precise Location of Hypocenters

Seismological Research Letters ◽

10.1785/gssrl.59.4.123 ◽

1988 ◽

Vol 59 (4) ◽

pp. 123-131 ◽

Cited By ~ 15

Author(s):

L. Himes ◽

W. Stauder ◽

R. B. Herrmann

Keyword(s):

Active Faults ◽

P Wave ◽

New Madrid Seismic Zone ◽

Supporting Evidence ◽

Seismic Zone ◽

Low Velocity ◽

Focal Mechanism Solutions ◽

Velocity Models ◽

Planar Surfaces ◽

New Madrid

Abstract The hypocenter locations of the larger and better recorded earthquakes of the New Madrid seismic zone are examined in order to determine how closely the hypocenters lie along planar surfaces, thus relating the foci to active fault surfaces. For this purpose more than 500 earthquakes of the region have been selected for study, based on the number (7 or more) of observing stations used in the initial hypocenter location and on the quality of the P-wave onset. These events are relocated using a joint hypocenter-velocity-depth (JHVD) algorithm. The relocated earthquakes are separated geographically into three trends: ARK, the southwest trending zone from Caruthersville, Missouri, to Marked Tree, Arkansas; DWM, the northeast trending zone from New Madrid to Charleston, Missouri; and CEN, the central, left-stepping offset zone from Ridgely, Tennessee, to New Madrid, Missouri. Vertical profiles taken along and across the ARK and DWM trends verify the strike and dip of dominantly strike slip motion on near vertical active faults along these trends. These results agree with previously determined composite focal mechanism solutions for these trends. No coherent picture has been obtained for the CEN trend. As a by-product of the study, velocity models from the JHVD inversion are found to be reasonably uniform throughout the New Madrid seismic zone, and to offer supporting evidence for the presence of a shallow low velocity zone in the central portion of the Mississippi embayment.

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