A Joint Inversion of Ground Deformation and Focal Mechanisms Data for Magmatic Source Modelling

2014 ◽  
Vol 171 (8) ◽  
pp. 1695-1704 ◽  
Author(s):  
Flavio Cannavò ◽  
Danila Scandura ◽  
Mimmo Palano ◽  
Carla Musumeci
Keyword(s):  
Ground Deformation ◽  
Joint Inversion ◽  
Focal Mechanisms ◽  
Magmatic Source

Joint Inversion of Rupture across a Fault Stepover during the 8 August 2017 Mw 6.5 Jiuzhaigou, China, Earthquake

2021 ◽  
Author(s):  
Yong Zhang ◽  
Wanpeng Feng ◽  
Xingxing Li ◽  
Yajing Liu ◽  
Jieyuan Ning ◽  
...  
Keyword(s):  
Joint Inversion ◽  
Strong Motion ◽  
Focal Mechanisms ◽  
High Rate ◽  
Fault System ◽  
Interferometric Synthetic Aperture Radar ◽  
Coseismic Slip ◽  
Jiuzhaigou Earthquake ◽  
Rupture Model ◽  
The Right

Abstract The 8 August 2017 Mw 6.5 Jiuzhaigou earthquake occurred in a tectonically fractured region in southwest China. We investigate the multifault coseismic rupture process by jointly analyzing teleseismic, strong-motion, high-rate Global Positioning System, and Interferometric Synthetic Aperture Radar (InSAR) datasets. We clearly identify two right-stepping fault segments and a compressional stepover based on variations in focal mechanisms constrained by coseismic InSAR deformation data. The average geometric parameters of the northwest and southeast segments are strike = 130°/dip = 57° and strike = 151°/dip = 70°, respectively. The rupture model estimated from a joint inversion of the seismic and geodetic datasets indicates that the rupture initiated on the southeastern segment and jumped to the northwestern segment, resulting in distinctive slip patches on the two segments. A 4-km-long coseismic slip gap was identified around the stepover, consistent with the aftershock locations and mechanisms. The right-stepping segmentation and coseismic rupture across the compressional stepover exhibited by the 2017 Jiuzhaigou earthquake are reminiscent of the multifault rupture pattern during the 1976 Songpan earthquake sequence farther south along the Huya fault system in three successive Ms∼7 events. Although the common features of fault geometry and stepover may control the similarity in event locations and focal mechanisms of the 2017 and 1976 sequences, the significantly wider (~15 km) stepover in the 1976 sequence likely prohibited coseismic rupture jumping and hence reduced seismic hazard.

Complex behaviour highlighted by earthquake aftershock and swarm sequences in Ubaye Region (French Western Alps). 

2021 ◽  
Author(s):  
Marion Baques ◽  
Louis De Barros ◽  
Maxime Godano ◽  
Hervé Jomard ◽  
Clara Duverger ◽  
...  
Keyword(s):  
Fault Plane ◽  
Joint Inversion ◽  
Fluid Pressure ◽  
Western Alps ◽  
Focal Mechanisms ◽  
High Rate ◽  
Double Difference ◽  
Complex Behaviour ◽  
Aftershock Sequences ◽  
Damaged Zone

<p>The Ubaye Region, where the city of Barcelonnette is settled, is the most seismically active region in the French Western Alps since at least two centuries. Seismicity in this area exhibits a dual behaviour, with mainshock-aftershock sequences alternating with abnormally high rate of seismicity associated with seismic swarms. Understanding processes triggering such a peculiar seismic behaviour is of primary importance in order to assess the seismic hazard in this region. The latest swarm activity started on February 26, 2012, with an earthquake of moment magnitude 4.2. It was followed two years later (on April 7, 2014) by a shock of magnitude Mw 4.8. From the first earthquake to the end of 2016, the seismic level has not returned to the background level and shares the same characteristics as a seismic swarm.</p><p>With the aim to discuss the seismogenic processes involved in the area, we focused on the two months following the 2014 mainshock (Mw=4.8). During this period, a dense temporary network (7 stations) was operating at a maximal distance of 10km from the epicentre area. We analysed this period starting with a double-difference relocation of ~ 6,000 earthquakes previously detected by template-matching. These hypocentres did not align on the fault plane of the 2014 mainshock, but on conjugated structures belonging to the 2-km wide damaged zone of the main fault plane and on remote structures with various orientations further away. We then computed 99 focal mechanisms from a joint inversion of P polarity and S/P ratio to clarify the geometry of the active structures. Many nodal planes are inconsistent with the structures deduced from the alignments of the earthquake locations. The stress-state orientation obtained from those focal mechanisms (σ<sub>1</sub> trending N27°± 5°, plunging 50°± 9°, a σ<sub>2</sub> trending N215°± 5°, plunging 40°± 9°, and a sub-horizontal σ<sub>3</sub> trending N122°± 3°) is consistent with those previously calculated in the area (Fojtíková and Vavryčuk, 2018). Nevertheless, some structures are unfavourably oriented to slip within this stress-field, suggesting that additional processes are required to explain them. As the presence of fluids was highlighted for the 2003-2004 and the 2012-2015 crisis, we calculated the fluid pressure needed to trigger slip on the planes from the focal mechanisms using Cauchy's equation. We found that a median fluid-overpressure of ~20 MPa (range between 0 to 50 MPa) is needed to cause slip.  Although the origin of fluids and how they are pressurized at depth remains open. The fluid processes seem to be the most favourable additional processes and were also proposed to explain the 2003-2004 crisis.</p>

scholarly journals Domino-style earthquakes along blind normal faults in Northern Thessaly (Greece): kinematic evidence from field observations, seismology, SAR interferometry and GNSS

2021 ◽  
Vol 58 ◽  
pp. 37
Author(s):  
Athanassios Ganas ◽  
Sotiris Valkaniotis ◽  
Pierre Briole ◽  
Anna Serpetsidaki ◽  
Vassilis Kapetanidis ◽  
...  
Keyword(s):  
Ground Deformation ◽  
Vertical Component ◽  
Normal Fault ◽  
Focal Mechanisms ◽  
Sar Interferometry ◽  
P Wave ◽  
Joint Analysis ◽  
Local Networks ◽  
Rupture Plane ◽  
Seismic Deformation

Here we present a joint analysis of the geodetic, seismological and geological data of the March 2021 Northern Thessaly seismic sequence, that were gathered and processed as of April 30, 2021. First, we relocated seismicity data from regional and local networks and inferred the dip-direction (NE) and dip-angle (38°) of the March 3, 2021 rupture plane. Furthermore, we used ascending and descending SAR images acquired by the Sentinel-1 satellites to map the co-seismic displacement field. Our results indicate that the March 3, 2021 Mw=6.3 rupture occurred on a NE-dipping, 39° normal fault located between the villages Zarko (Trikala) and Damasi (Larissa). The event of March 4, 2021 occurred northwest of Damasi, along a fault oriented WNW-ESE and produced less deformation than the event of the previous day. The third event occurred on March 12, 2021 along a south-dipping normal fault. We computed 22 focal mechanisms of aftershocks with M≥4.0 using P-wave first motion polarities. Nearly all focal mechanisms exhibit normal kinematics or have a dominant normal dip-slip component. The use of InSAR was crucial to differentiate the ground deformation between the ruptures. The majority of deformation occurs in the vertical component, with a maximum of 0.39 m of subsidence over the Mw=6.3 rupture plane, south and west of Damasi. A total amount of 0.3 m horizontal displacement (E-W) was measured. We also used GNSS data (at 30-s sampling interval) from twelve permanent stations near the epicentres to obtain 3D seismic offsets of station positions. Only the first event produces significant displacement at the GNSS stations (as predicted by the fault models, themselves very well constrained by InSAR). We calculated several post-seismic interferograms, yet we have observed that there is almost no post-seismic deformation, except in the footwall area (Zarkos mountain). This post-seismic deformation is below the 7 mm level (quarter of a fringe) in the near field and below the 1 mm level at the GNSS sites. The cascading activation of the three events in a SE to NW direction points to a pattern of domino-style earthquakes, along neighbouring fault segments. The kinematics of the ruptures point to a counter-clockwise change in the extension direction of the upper crust (from NE-SW near Damasi to N-S towards northwest, near Verdikoussa).

scholarly journals Joint Regional Waveform, First-Motion Polarity, and Surface Displacement Moment Tensor Inversion of the 3 September 2017 North Korean Nuclear Test

2021 ◽  
Vol 1 (2) ◽  
pp. 107-116
Author(s):  
Rodrigo Chi-Durán ◽  
Douglas S. Dreger ◽  
Arthur J. Rodgers ◽  
Avinash Nayak
Keyword(s):  
Ground Deformation ◽  
Joint Inversion ◽  
Moment Tensor ◽  
Permanent Deformation ◽  
Nuclear Test ◽  
Inversion Method ◽  
Seismic Moment Tensor ◽  
Source Type ◽  
Best Fitting ◽  
First Motion

Abstract The 3 September 2017 Mw 5.2 North Korean underground nuclear test (DPRK2017) is the largest man-made explosion with surface displacements observed by Synthetic Aperture Radar (SAR) and showed as much as 3.5 m of horizontal permanent deformation. Although regional distance waveform-based seismic moment tensor (MT) inversion methods successfully identify this event as an explosion, the inverted solutions do not fit the SAR displacement field well. To better constrain the source, we developed an MT source-type inversion method that incorporates surface ground deformation (accounting for free-surface topography), regional seismic waveforms, and first-motion polarities. We applied the source-type inversion over a grid of possible source locations to find the best-fitting location, depth, and point-source MT for the event. Our best-fitting MT solution achieves ∼70% horizontal geodetic fit, ∼80% waveform fit, and 100% fit in the first-motion polarities. The joint inversion narrows the range of acceptable source types improving discrimination, and reduces the uncertainty in scalar moment and estimated yield. The method is transportable and can be applied to other types of events that may have measurable geodetic signals such as underground mine collapses and volcanic events.

New insight into the December 2018 Etna eruption through the joint inversion of ground deformation and gravity data

2020 ◽  
Author(s):  
Mahak Singh Chauhan ◽  
Flavio Cannavò ◽  
Daniele Carbone ◽  
Filippo Greco
Keyword(s):  
Search Algorithm ◽  
Ground Deformation ◽  
Joint Inversion ◽  
Gravity Data ◽  
Monitoring Network ◽  
Pattern Search ◽  
Gravity Change ◽  
Model Parameters ◽  
Geometrical Parameters ◽  
Superconducting Gravimeters

<p>We focus on the eruption of Mt. Etna which took place on 24 December, 2018. The eruption occurred after a month of unrest and was accompanied by a seismic swarm that culminated in the M4.9 earthquake on the 26th, with epicentre on the eastern flank of the volcano. We jointly analyse ground deformation and gravity data to estimate the geometrical and kinematic parameters of the source structure, together with the density of the intruding material. The data used in this study were recorded by stations in the INGV-OE monitoring network (21 GPS stations and 2 gravity stations equipped with superconducting gravimeters), during the interval of 23 to 28 December (pre to post eruption). We assume a dike-type source for the forward calculation in the defined objective function. A pattern search algorithm (PSA) is used for the iterative minimization of the misfit error. In order to estimate the posterior probability density function (PDFs) of the model parameters, we also use a Markov Chain Monte Carlo (MCMC) approach. Indeed, the calculated PDFs provide more information about the uncertainties of the model parameters, which helps to understand overall tendencies of the solutions. We first test the constrained inversion of the gravity data, to calculate the density of eruptive magmatic body, by fixing the geometrical parameters of the dike, previously retrieved through inversion of the deformation data only. Using this approach, it is possible to suitable explain the deformation data and the gravity change observed at the station in the near field (MNT), while the gravity change at the other station (SLN) remain unexplained. We then invert jointly both deformation and gravity datasets, in order to adequately fit all the observations. The final model gives a density value of ~1.8-2.0 g/cm3. This value is significantly lower than the density of bubble-free magma and indicates either the involvement of gas in the intrusive process, or the formation of dry fissures during the emplacement of the dyke.</p>

scholarly journals New insight into the 2011-2012 unrest and eruption of El Hierro Island (Canary Islands) based on integrated geophysical, geodetical and petrological data

2015 ◽  
Vol 58 (5) ◽  
Author(s):  
Stavros Meletlidis ◽  
Alessio Di Roberto ◽  
Itahiza Domínguez Cerdeña ◽  
Massimo Pompilio ◽  
Laura García-Cañada ◽  
...  
Keyword(s):  
Canary Islands ◽  
Upper Mantle ◽  
Rift Zone ◽  
Ground Deformation ◽  
Magma Ascent ◽  
Research Approach ◽  
Magmatic Source ◽  
El Hierro ◽  
Vertical Ground ◽  
Insight Into

<p>A shallow water eruption started on October 10, 2011, ~2 km south off the coast of El Hierro (Canary Islands, Spain). The eruption lasted about five months and ended by early March 2012. Three months of unrest preceded this event with more than 10,000 localized earthquakes and up to 6 cm of vertical ground deformation. In the Canary Islands, this is the first eruption to be monitored by the network of Instituto Geográfico National (IGN) since the very beginning of the seismic unrest. This provided unprecedented time series that include geophysical (seismic and gravimetric), geodetic, geochemical and petrological data. In this work we discuss and interpret these data in order to describe the mechanisms of 2011-2012 El Hierro eruption, including ascent from magmatic source, a crustal storage, and the final intrusion in the South Rift before the eruption. Our research approach provides a multidisciplinary view of the dynamics of magma ascent and improves previous interpretations formulated during or shortly after the end of the eruption. According to our results, a major intrusion occurred beneath and around preexisting high-density magmatic bodies, localized at depth below the central part of the island. After a failed attempt to reach the surface through a low fractured zone located below the central-northern part of the island, the ascending magma finally found its way nearby the El Hierro South Rift Zone and erupted off the coast of La Restinga village, 350 m below sea level. The eruption was fed by the ascent of an important volume of material from the upper mantle that was emplaced near the crust-mantle boundary and progressively tapped during the eruption.</p>

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