Aftershock signature of the M7.5 Palu 2018 supershear rupture from a rapidly deployed nodal array 

2021 ◽  
Author(s):  
Karen Lythgoe ◽  
Muzi Muzli ◽  
Win Oo ◽  
Hongyu Zeng ◽  
Rahmat Triyono ◽  
...  
Keyword(s):  
Template Matching ◽  
Earthquake Swarm ◽  
Middle Part ◽  
Fault System ◽  
Double Difference ◽  
Ground Shaking ◽  
Moment Tensors ◽  
Short Period ◽  
Waveform Modelling ◽  
Rupture Speed

<p>Supershear earthquakes have significant implications for seismic hazard, in terms of  ground shaking and aftershock pattern. It has been suggested that supershear ruptures are associated with fewer aftershocks on the supershear rupture segment, however this needs to be tested using high resolution event locations. Current aftershock catalogues for the M7.5 Palu 2018 supershear rupture are not of sufficient resolution to identify any characteristic aftershock pattern. Additionally it is unclear whether the supershear rupture speed occurred from the time of earthquake initiation, or at a later time on a certain segment of the fault.</p><p>We deployed a nodal array to record aftershocks following the main event. The array comprised of twenty short-period nodes, which can be deployed rapidly, making them ideal for post-rupture investigations in areas of sparse coverage. We expand the earthquake catalogue by applying template matching to the nodal array data. We then relocate seismicity recorded by the array using a double difference method. We also relocate seismicity that occurred before the array was active, using a relative relocation method. To do this, we calibrate the more distant permanent stations using events well-located by the nodal array. We further derive moment tensors for the largest events by waveform modelling using short-period and broadband records.</p><p>Our results show that the aftershocks cluster at the northern and southern extents of rupture. There is a relative dearth of aftershocks in the middle part of the rupture, particularly in the Palu valley, where rupture terminated to the surface. The fault here is a long and straight distinctive geomorphic feature. Many secondary faults were triggered, particularly in the southern Sapu valley fault system. An earthquake swarm was triggered 1 month after the main event on a strike-slip fault 200km away.</p>

Analysis of the 15 December 2017 Mw 6.5 and the 23 January 2018 Mw 5.9 Java Earthquakes

2020 ◽  
Vol 110 (6) ◽  
pp. 3050-3063
Author(s):  
Anne Meylani Magdalena Sirait ◽  
Anne S. Meltzer ◽  
Felix Waldhauser ◽  
Joshua C. Stachnik ◽  
Daryono Daryono ◽  
...  
Keyword(s):  
Moment Tensor ◽  
Fluid Pressure ◽  
Fault System ◽  
Double Difference ◽  
Northern Coast ◽  
Eurasian Plate ◽  
Slab Geometry ◽  
Plate Interface ◽  
Upward Migration ◽  
Ground Shaking

ABSTRACT The west part of Java sits at the transition from oblique subduction of the Australian plate under the Sunda block of the Eurasian plate along Sumatra to orthogonal convergence along central and eastern Java. This region has experienced several destructive earthquakes, the 17 July 2006 Mw 7.7 earthquake and tsunami off the coast of Pangandaran and the 2 September 2009 Mw 7 earthquake, located off the coast of Tasikmalaya. More recently, on 15 December 2017, an Mw 6.5 earthquake occurred off the coast near Pangandaran, and, on 23 January 2018, an Mw 5.9 earthquake occurred offshore Lebak, between Pelabuhan Ratu and Ujung Kulon. Ground shaking and damage occurred locally and in Jakarta on the northern coast of Java. In this study, we use the double-difference technique to relocate both mainshocks and 10 months of seismicity (228 events) following the earthquakes. The relocation result improved the mainshock locations and depth distribution of earthquakes. Moment tensor of the December 2017 event located the hypocenter at ∼108  km depth within the subducting slab. The best-fit relocation places the depth at 61 km, close to the slab interface. Aftershocks occur between 68 and 86 km depth and align along a steeper plane than slab geometry models. The January 2018 event is located at ∼46  km depth. Aftershocks form a near-vertical, pipe-like structure from the plate interface to ∼10  km depth. A burst of aftershocks immediately following the mainshock shows a shallowing upward trend at a rate of ∼2  km/hr, suggesting that a fluid pressure wave released from the oceanic crust is causing brittle failure in the overriding plate, followed by upward migration of fluids. Five months later, shallow (<25  km) seismicity collocates with background seismicity, suggesting the January 2018 event activated the Pelabuhan Ratu fault system close to the coast.

Spatial and temporal variations of seismicity during the Maurienne swarm (French Alps): short- and long-term migrations and b-value dependence with depth

2021 ◽  
Author(s):  
Riccardo Minetto ◽  
Agnès Hemlstetter ◽  
Philippe Guéguen ◽  
Mickaël Langlais
Keyword(s):  
Template Matching ◽  
B Value ◽  
Temporal Variations ◽  
Fault System ◽  
Double Difference ◽  
French Alps ◽  
Vertical Fault ◽  
Spatio Temporal ◽  
The One

<p>We analyse the spatio-temporal variations of the seismicity recorded during the Maurienne swarm. The Maurienne swarm occurred between 2017 and 2018 in the French Alps in the central part of the external crystalline massif of Belledonne. This massif extends for more than 120km in N30 direction, it is bounded to the west by the wide topographic depression of the Isère valley and the Combe de Savoie, and it is crosscut by the Maurienne valley.  The location and the 3D shape of the seismic swarm are consistent with an outcroping N80 vertical fault zone. The seismic activity is interpreted as a result of the reactivation of this inherited vertical fault system. The largest event had a magnitude of 3.5.</p><p><br>We used a catalog of 58000 events that were detected using template-matching and relocated with a double-difference method.  <br>We show that the swarm is characterised by short-term (days) and long-term (months) migrations that may be related to the presence of fluids. <br>We also observe that the b-value decreases with depth and we discuss how this variation may due to shallow fault systems whose geometry differs from the one of the main fault system. <br>Part of the events occurred when only one station was active. This study shows that, by grouping earthquakes into groups of similar events (clusters), it is possible to study spatio-temporal variations in such conditions.</p>

scholarly journals Complex Fault Geometry of the 2020 Mww 6.5 Monte Cristo Range, Nevada, Earthquake Sequence

2021 ◽  
Vol 92 (3) ◽  
pp. 1876-1890 ◽  
Author(s):  
Christine J. Ruhl ◽  
Emily A. Morton ◽  
Jayne M. Bormann ◽  
Rachel Hatch-Ibarra ◽  
Gene Ichinose ◽  
...  
Keyword(s):  
Salt Marsh ◽  
Normal Fault ◽  
Aftershock Sequence ◽  
Fault System ◽  
Double Difference ◽  
Moment Tensors ◽  
Vertical Fault ◽  
Surface Ruptures ◽  
Mina Deflection ◽  
Rapid Deployment

Abstract On 15 May 2020 an Mww 6.5 earthquake occurred beneath the Monte Cristo Range in the Mina Deflection region of western Nevada. Rapid deployment of eight temporary seismic stations enabled detailed analysis of its productive and slowly decaying aftershock sequence (p=0.8), which included ∼18,000 autodetected events in 3.5 months. Double-difference, waveform-based relative relocation of 16,714 earthquakes reveals a complex network of faults, many of which cross the inferred 35-km-long east–northeast-striking, left-lateral mainshock rupture. Seismicity aligns with left-lateral, right-lateral, and normal mechanism moment tensors of 128 of the largest earthquakes. The mainshock occurred near the middle of the aftershock zone at the intersection of two distinct zones of seismicity. In the western section, numerous subparallel, shallow, north-northeast-striking faults form a broad flower-structure-like fault mesh that coalesces at depth into a near-vertical, left-lateral fault. We infer the near-vertical fault to be a region of significant slip in the mainshock and an eastward extension of the left-lateral Candelaria fault. Near the mainshock hypocenter, seismicity occurs on a northeast-striking, west-dipping structure that extends north from the eastern Columbus Salt Marsh normal fault. Together, these two intersecting structures bound the Columbus Salt Marsh tectonic basin. East of this intersection and the mainshock hypocenter, seismicity occurs in a narrow, near-vertical, east-northeast-striking fault zone through to its eastern terminus. At the eastern end, the aftershock zone broadens and extends northwest toward the southern extension of the northwest-striking, right-lateral Petrified Springs fault system. The eastern section hosts significantly fewer aftershocks than the western section, but has more moment release. We infer that shallow aftershocks throughout the system highlight fault-fracture meshes that connect mapped fault systems at depth. Comparing earthquake data with surface ruptures and a simple geodetic fault model sheds light on the complexity of this recent M 6.5 Walker Lane earthquake.

The 25 October, 2018 Zakynthos (Greece) earthquake: seismic activity at the transition between a transform fault and a subduction zone.

2020 ◽  
Author(s):  
P Papadimitriou ◽  
V Kapetanidis ◽  
A Karakonstantis ◽  
I Spingos ◽  
K Pavlou ◽  
...  
Keyword(s):  
Spatial Clustering ◽  
Accretionary Prism ◽  
Velocity Model ◽  
Strike Slip ◽  
Double Difference ◽  
Strain Partitioning ◽  
Transform Fault ◽  
Fault Plane Solutions ◽  
The North ◽  
Waveform Modelling

Summary The properties of the Mw = 6.7 earthquake that took place on 25 October 2018, 22:54:51 UTC, ∼50 km SW of the Zakynthos Island, Greece, are thoroughly examined. The main rupture occurred on a dextral strike-slip, low-angle, east-dipping fault at a depth of 12 km, as determined by teleseismic waveform modelling. Over 4000 aftershocks were manually analysed for a period of 158 days. The events were initially located with an optimal 1D velocity model and then relocated with the double-difference method to reveal details of their spatial distribution. The latter spreads in an area spanning 80 km NNW-SSE and ∼55 km WSW-ENE. Certain parts of the aftershock zone present strong spatial clustering, mainly to the north, close to Zakynthos Island, and at the southernmost edge of the sequence. Focal mechanisms were determined for 61 significant aftershocks using regional waveform modelling. The results revealed characteristics similar to the mainshock, with few aftershocks exhibiting strike-slip faulting at steeper dip angles, possibly related to splay faults on the accretionary prism. The slip vectors that correspond to the east-dipping planes are compatible with the long-term plate convergence and with the direction of coseismic displacement on the Zakynthos Island. Fault-plane solutions in the broader study area were inverted for the determination of the regional stress-field. The results revealed a nearly horizontal, SW-NE to E-W-trending S1 and a more variable S3 axis, favouring transpressional tectonics. Spatial clusters at the northern and southern ends of the aftershock zone coincide with the SW extension of sub-vertical along-dip faults of the segmented subducting slab. The mainshock occurred in an area where strike-slip tectonics, related to the Cephalonia Transform Fault and the NW Peloponnese region, gradually converts into reverse faulting at the western edge of the Hellenic subduction. Plausible scenarios for the 2018 Zakynthos earthquake sequence include a rupture on the subduction interface, provided the slab is tilted eastwards in that area, or the reactivation of an older east-dipping thrust as a low-angle strike-slip fault that contributes to strain partitioning.

scholarly journals Insights into Mechanical Properties of the 1980 Irpinia Fault System from the Analysis of a Seismic Sequence

Geosciences ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 28
Author(s):  
Gaetano Festa ◽  
Guido Maria Adinolfi ◽  
Alessandro Caruso ◽  
Simona Colombelli ◽  
Grazia De Landro ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Early Warning Systems ◽  
Fault System ◽  
Minimum Size ◽  
Double Difference ◽  
Warning Systems ◽  
Initiation Mechanism ◽  
Earthquake Early Warning Systems ◽  
The One

Seismic sequences are a powerful tool to locally infer geometrical and mechanical properties of faults and fault systems. In this study, we provided detailed location and characterization of events of the 3–7 July 2020 Irpinia sequence (southern Italy) that occurred at the northern tip of the main segment that ruptured during the 1980 Irpinia earthquake. Using an autocorrelation technique, we detected more than 340 events within the sequence, with local magnitude ranging between −0.5 and 3.0. We thus provided double difference locations, source parameter estimation, and focal mechanisms determination for the largest quality events. We found that the sequence ruptured an asperity with a size of about 800 m, along a fault structure having a strike compatible with the one of the main segments of the 1980 Irpinia earthquake, and a dip of 50–55° at depth of 10.5–12 km and 60–65° at shallower depths (7.5–9 km). Low stress drop release (average of 0.64 MPa) indicates a fluid-driven initiation mechanism of the sequence. We also evaluated the performance of the earthquake early warning systems running in real-time during the sequence, retrieving a minimum size for the blind zone in the area of about 15 km.

Approximate method to estimate the short-period strong motion spectra on bedrock

1981 ◽  
Vol 71 (2) ◽  
pp. 491-505
Author(s):  
Katsuhiko Ishida
Keyword(s):  
Earthquake Swarm ◽  
Strong Motion ◽  
Fourier Amplitude ◽  
Period Range ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Short Period ◽  
Amplitude Spectra ◽  
Low Pass ◽  
Parkfield Earthquake

abstract The methodology to estimate the strong motion Fourier amplitude spectra in a short-period range (T ≦ 1 to 2 sec) on a bedrock level is discussed in this paper. The basic idea is that the synthetic strong motion Fourier spectrum F˜A(ω) calculated from smoothed rupture velocity model (Savage, 1972) is approximately similar to that of low-pass-filtered strong earthquake ground motion at a site in a period range T ≧ 1 to 2 sec: F˜A(ω)=B˜(ω)·A(ω). B˜(ω) is an observed Fourier spectrum on a bedrock level and A(ω) is a low-pass filter. As a low-pass filter, the following relation, A ( T ) = · a · T n a T n + 1 , ( T = 2 π / ω ) , is assumed. In order to estimate the characteristic coefficients {n} and {a}, the Tokachi-Oki earthquake (1968), the Parkfield earthquake (1966), and the Matsushiro earthquake swarm (1966) were analyzed. The results obtained indicate that: (1) the coefficient {n} is nearly two for three earthquakes, and {a} is nearly one for the Tokachi-Oki earthquake, eight for the Parkfield earthquake, and four for the Matsushiro earthquake swarm, respectively; (2) the coefficient {a} is related with stress drop Δσ as (a = 0.07.Δσ). Using this relationship between {a} and Δσ, the coefficients {a} of past large earthquakes were estimated. The Fourier amplitude spectra on a bedrock level are also estimated using an inverse filtering method of A ( T ) = a T 2 a T 2 + 1 .

Repeating earthquakes follow afterslip gradient in the aftermath of the 16th April 2016 M7.8 Pedernales earthquake in Ecuador

2021 ◽  
Author(s):  
Caroline Chalumeau ◽  
Keyword(s):  
Template Matching ◽  
Earthquake Forecasting ◽  
Double Difference ◽  
Recurrence Time ◽  
Fault Mechanics ◽  
Aseismic Slip ◽  
Earthquake Triggering ◽  
Repeating Earthquakes ◽  
Waveform Cross Correlation ◽  
One Year

<p>Repeating earthquakes are earthquakes that repeatedly break a single, time-invariant fault patch. They are generally associated with aseismic slip, which is thought to load asperities, leading to repeated rupture. Repeating earthquakes are therefore useful tools to study aseismic slip and fault mechanics, with possible applications to earthquake triggering, loading rates and earthquake forecasting.</p><p>In this study, we analyze one year of aftershocks following the 16<sup>th</sup> April 2016 Mw 7.8 Pedernales earthquake in Ecuador to find repeating families, using data recorded by permanent and temporary seismological stations. In our area, seismicity during both the inter-seismic and post-seismic periods has been previously linked to aseismic slip. We calculate waveform cross-correlation coefficients (CC) on all available catalogue events, which we use to sort events into preliminary families, using a minimum CC of 0.95. These events were then stacked and used to perform template-matching on the continuous data. In total, 376 earthquakes were classified into 62 families of 4 to 15 earthquakes, including 8 from the one-year period before the mainshock. We later relocated these earthquakes using a double-difference method, which confirmed that most of them did have overlapping sources.</p><p>Repeating earthquakes seem to concentrate largely around the areas of largest afterslip release, where afterslip gradient is the highest. We also find an increase in the recurrence time of repeating events with time after the mainshock, over the first year of the postseismic period, which highlights a possible timeframe for the afterslip’s deceleration. Our results suggest that while most repeating aftershocks are linked to afterslip release, the afterslip gradient may play a bigger role in determining their location than previously thought.</p>

scholarly journals Neogene-Quaternary tectonic regime and macroseismic observations in the Tyrnavos-Elassona broader epicentral area of the March 2021, intense earthquake sequence

2021 ◽  
Vol 58 ◽  
pp. 200
Author(s):  
Dimitrios Galanakis ◽  
Sotiris Sboras ◽  
Garyfalia Konstantopoulou ◽  
Markos Xenakis
Keyword(s):  
Normal Fault ◽  
Fault Scarp ◽  
Focal Mechanisms ◽  
Fault System ◽  
Spatiotemporal Evolution ◽  
Surface Rupture ◽  
Alluvial Deposits ◽  
Epicentral Area ◽  
Ground Shaking ◽  
Macroseismic Observations

On March 3, 2021, a strong (Mw6.3) earthquake occurred near the towns of Tyrnavos and Elassona. One day later (March 4), a second strong (Mw6.0) earthquake occurred just a few kilometres toward the WNW. The aftershock spatial distribution and the focal mechanisms revealed NW-SE-striking normal faulting. The focal mechanisms also revealed a NE-SW oriented extensional stress field, different from the orientation we knew so far (ca. N-S). The magnitude and location of the two strongest shocks, and the spatiotemporal evolution of the sequence, strongly suggest that two adjacent fault segments were ruptured respectively. The sequence was followed by several coseismic ground deformational phenomena, such as landslides/rockfalls, liquefaction and ruptures. The landslides and rockfalls were mostly associated with the ground shaking. The ruptures were observed west of the Titarissios River, near to the Quaternary faults found by bore-hole lignite investigation. In the same direction, a fault scarp separating the alpidic basement from the alluvial deposits of the Titarissios valley implies the occurrence of a well-developed fault system. Some of the ground ruptures were accompanied by extensive liquefaction phenomena. Others cross-cut reinforced concrete irrigation channels without changing their direction. We suggest that this fault system was partially reactivated, as a secondary surface rupture, during the sequence as a steeper splay of a deeper low-to-moderate angle normal fault.

scholarly journals Impact of Slab Thickness on Reinforced Concrete Buildings using Fragility Curves

2020 ◽  
Vol 8 (5) ◽  
pp. 4533-4538
Keyword(s):  
Reinforced Concrete ◽  
Fragility Curves ◽  
Structural Response ◽  
Software Tool ◽  
Slab Thickness ◽  
Ground Shaking ◽  
Code Of Practice ◽  
Short Period ◽  
Rc Frame Structures ◽  
The Impact

Earthquakes are the natural disaster occurring since years but during the last two decades they are causing huge looses whether it may economic or to life. This paper focuses to evaluate the seismic performance of various building confirming to Indian standard criteria for earthquake resistant design of structures and ductile detailing of reinforced concrete structures subjected to seismic Forces-code of practice, Bureau of Indian Standards, both as per the revised codes in the year 2016. Due to ground shaking, seismic loads are the governing load and thus it becomes necessary to assess the conditional probability of structural response. Use of HAZUS methodology is followed to construct seismic fragility curves as it is well-organized and defined approach. Spectral displacement plays the functional parameter to derive the expected damage for fragility. This work represented here is compiled by means of procedure for establishing the fragility curves for three typical Reinforced Concrete (RC) frame structures having variations resembling 3 storey intended for short-period structures, 6 storey used for medium-period structures and 12 storey representing long-period structures using SAP2000 as a software tool for analyzing the structure. Furthermore an attempt is made for focus on the variation of one of the major structural configuration i.e. slab thickness which is not certainly paid attention as compared to columns and beams. Slabs adds additional stiffness to the structure which can enlighten how it behaviour would be when subjected to ground excitation. As a result, the fragility curves are plotted to study the impact due to slab thickness in order they are carefully selected while design.

scholarly journals The 31 March 2020 Mw 6.5 Stanley, Idaho, Earthquake: Seismotectonics and Preliminary Aftershock Analysis

2020 ◽  
Author(s):  
Lee M. Liberty ◽  
Zachery M. Lifton ◽  
T. Dylan Mikesell
Keyword(s):  
Surface Displacement ◽  
Volcanic Belt ◽  
Normal Fault ◽  
Fault System ◽  
Basin And Range Province ◽  
Ground Shaking ◽  
The North ◽  
Show Evidence ◽  
Tectonic Framework ◽  
Tectonic Belt

Abstract We report on the tectonic framework, seismicity, and aftershock monitoring efforts related to the 31 March 2020 Mw 6.5 Stanley, Idaho, earthquake. The earthquake sequence has produced both strike-slip and dip-slip motion, with minimal surface displacement or damage. The earthquake occurred at the northern limits of the Sawtooth normal fault. This fault separates the Centennial tectonic belt, a zone of active seismicity within the Basin and Range Province, from the Idaho batholith to the west and Challis volcanic belt to the north and east. We show evidence for a potential kinematic link between the northeast-dipping Sawtooth fault and the southwest-dipping Lost River fault. These opposing faults have recorded four of the five M≥6 Idaho earthquakes from the past 76 yr, including 1983 Mw 6.9 Borah Peak and the 1944 M 6.1 and 1945 M 6.0 Seafoam earthquakes. Geological and geophysical data point to possible fault boundary segments driven by pre-existing geologic structures. We suggest that the limits of both the Sawtooth and Lost River faults extend north beyond their mapped extent, are influenced by the relic trans-Challis fault system, and that seismicity within this region will likely continue for the coming years. Ongoing seismic monitoring efforts will lead to an improved understanding of ground shaking potential and active fault characteristics.

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