The seismic history of the Mosha fault, the largest and most active fault of Eastern Tehran metropolis, and its relation to the Damavand active volcano, the highest mountain in the Middle East, is investigated. We deduce that the central Mosha, near the Damavand, has a higher seismicity than either its western or eastern segments. On 7 May 2020, an Mw 5.1 earthquake occurred on the central Mosha, about 40 km east of Tehran and 10 km southwest of the Damavand crest, and it was felt intensely in Tehran. Its rupture is imaged and located in a region that presented a relative seismic quiescence compared to its eastern and western parts, during the last 14 years, suggesting its partial locking and heterogeneous distribution of fault frictional strength on this segment of Mosha. Its significant directivity to the west is confirmed by the mainshock rupture model, its PGA distribution, and distribution of early aftershocks. The rupture model suggests a relatively small stress drop of 2.6 bar, which is consistent with the comparatively high rupture dimension of 9 km for a Mw 5.1 earthquake, and indicates the easy rupture expansion on the central Mosha near the Damavand Volcano. The central Mosha experienced earthquakes in 1930, 1955, and 1983, as well as high microseismic activity and the 2020 seismic sequence, all of which strongly point to a possible influence of the Damavand Volcano on the seismicity of the central Mosha. This is corroborated by the observation of hydrothermal zones on the Mosha fault and the extension of a sill-like Damavand young magma chamber until central Mosha in tomography studies. We propose that the existing heat may increase the pore pressure on the fault, which lowers the effective normal stress, facilitates the nucleation-expansion of the rupture, and unclamps the fault. Damavand could act as a fuse and nucleate earthquakes, and if the rupture extends toward the west, it could have a significant directivity effect on low-frequency seismic waves that reach Tehran without attenuation and affect tall structures. In addition, high site amplification for frequencies up to 16 Hz due to the deep sedimentary basin, mainly in the mid-city of Tehran, will be remarkable for short buildings.
<div><span>Seismic history of the North Tabriz fault (NTF), the main active fault of Northwestern Iran near Tabriz city, and its relation to the Sahand active Volcano (SND), the second high mountain of the NW Iran, and to the 11 August 2012 Ahar-Varzaghan earthquake doublet (Mw6.5&6.3) (AVD), is investigated. I infer that before AVD seismicity of the central segment of NTF close to SND was very low compared to its neighbor segments. Magmatic activities and thermal springs near central NTF close to Bostan-Abad city and low-velocity anomalies reported beneath SND toward NTF in tomography studies suggest that the existing heat due to SND magma chamber has increased the pore-fluid pressure that overcomes the effective normal stress on the central NTF, resulting in its creep behaviour. Two peaks of cumulative scalar seismic moments of earthquakes observed on both lobes of the creeping segment, confirming the strong difference in the deformation rate between these segments. On 2012, AVD struck in the 50 km North of NTF, in the same longitude range to SND and with the same right-lateral strike-slip mechanism to NTF, as a result of partial transfer of the right-lateral deformation of NW Iran toward the North of NTF on the Ahar-Varzaghan fault system. A cumulative aseismic slip equal to an Mw6.8 event is estimated for the creeping segment of NTF, posing half of the 7mmy-1 geodetic deformation has happened in the creep mode. This event has transferred a positive Coulomb stress field of >1 bar on the AVD and triggered them. Also, the western and eastern NTF segments received >4 bar of positive Coulomb stresses from the creeping segment and are probable nucleation locations for future earthquakes on NTF. The observed creep may be the reason for the NTF segmentation during the 1721AD M7.6 and 1780 AD M7.4 historical earthquakes.</span></div>
Abstract Using template matching and GPS data, we investigate the evolution of seismicity and observable deformation in Central Apennines. Seismicity appears more persistent at the base of the seismogenic layer than in the shallower crust. Diffuse activity is reported on segments at depth, alternating along strike with apparent quiescence on segments that experienced one or more Mw 6+ earthquakes in 1997, 2009, and 2016. Central Apennines are likely underlain by a sizeable shear zone with areas of diffuse seismicity bounding shallow normal faults where Mw 6+ earthquakes occurred. The deformation observed at the surface seems to follow the seismicity variations at the base of seismogenic layer along the Apenninic chain. Principal and independent component analyses of GPS data exhibit a transient when the 2016 foreshock sequence starts. This transient propagated northward from the Campotosto fault up to the Alto Tiberina fault system and has likely loaded the Mw 6+ 2016 earthquake sequence.
The 2019-2020 Southwest Puerto Rico earthquake sequence ruptured multiple faults with several moderate magnitude earthquakes. Here we investigate the seismotectonics of this fault system using high precision hypocenter relocation and inversion of the near-field strong motions of five largest events in the sequence (5.6≤Mw≤6.4) for kinematic rupture models. The Mw6.4 mainshock occurred on an NE striking, SE dipping normal fault. The rupture nucleated offshore ~15 km SE of Indios at the depth of 8.6 km and extended SW-NE and up-dip with an average speed of 1.55 km/s, reaching the seafloor and shoreline after about 8 seconds. The 6th of January, 2020 (10:32:23) Mw5.7 and the 7th of January, 2020 (11:18:46) Mw5.8 events occurred on two E-SE striking, near-vertical, left-lateral strike-slip faults. However, the 7th January, 2020 (08:34:05) Mw5.6 normal faulting aftershock which occurred only 10 minutes after the Mw6.4 normal faulting mainshock, ruptured on a fault with almost the same strike as the mainshock but situated ~8 km further E, forming a set of parallel faults in the fault system. On 11th January 2020, a Mw6.0 earthquake occurred on a N-NE striking, W dipping fault, orthogonal to the faults hosting the strike-slip earthquakes. We apply template matching for the detection of missed, small magnitude earthquakes to study the spatial evolution of the main part of the sequence. Using the template matching results along with GPS analysis, we image the temporal evolution of a foreshock sequence (Caja swarm). We propose that the swarm and the main sequence were a response to a tectonic transient that most affected the whole Puerto Rico island.
Abstract We combine active and passive acoustic measurements to improve the spatio-temporal imaging of hydraulic fracture growth performed under true triaxial confinement in the laboratory. 64 active piezo-electric transducers (54 P waves, 10 S waves) work in source (32) - receivers (32) mode to perform an acoustic survey at repetitive intervals (every 10 seconds) during a hydraulic fracture growth experiment. The analysis of the evolution of the active acoustic monitoring changes allow to image the evolution of the fracture front (via an inversion of the active acoustic waves diffracted by the fracture front). An additional 16 piezoelectric transducers are pre-amplified and work in passive mode continuously recording at 10MHz. We present a nearly-automatic passive signal processing, acoustic emission detection, and location algorithm. This allows to record, detect and to locate acoustic emissions associated with fracture initiation and growth in between the active acoustic measurement sequences. Using a hydraulic fracturing test performed in gabbro, we discuss how active and passive acoustic monitoring complements one another and bring different type of information on hydraulic fracture growth.
Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Other. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v2]Long-term triggered seismicity on the Mosha fault by Damavand Volcano, N-Iran, Implications on the seismic hazard of Tehran metropolisAuthorsSeyyedmaalekMomeniiDRaulMadariagaSee all authors Seyyedmaalek MomeniiDCorresponding Author• Submitting AuthorEPFL, Geo-Energy Lab – Gaznat Chair on Geo-EnergyiDhttps://orcid.org/0000-0002-6170-7435view email addressThe email was not providedcopy email addressRaul MadariagaEcole Normale Superieureview email addressThe email was not providedcopy email address
Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Geophysical Journal International. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v1]Long-term induced seismicity on the Mosha fault by Damavand Volcano, N-Iran, Implications on the seismic hazard of Tehran metropolisAuthorsSeyyedmaalekMomeniiDRaulMadariagaSee all authors Seyyedmaalek MomeniiDCorresponding Author• Submitting AuthorEPFL, Geo-Energy Lab – Gaznat Chair on Geo-EnergyiDhttps://orcid.org/0000-0002-6170-7435view email addressThe email was not providedcopy email addressRaul MadariagaEcole Normale Superieureview email addressThe email was not providedcopy email address
Earth and Space Science Open Archive PosterOpen AccessYou are viewing the latest version by default [v1]Long-term induced seismicity on the Mosha fault by the Damavand Volcano, N-Iran, Implications for the seismic hazard of the Tehran metropolisAuthorsSeyyedmaalekMomeniiDRaulMadariagaiDSee all authors Seyyedmaalek MomeniiDCorresponding Author• Submitting AuthorThe Abdus Salam ICTPiDhttps://orcid.org/0000-0002-6170-7435view email addressThe email was not providedcopy email addressRaul MadariagaiDEcole Normale SuperieureiDhttps://orcid.org/0000-0003-2524-9489view email addressThe email was not providedcopy email address
