Seismic Gap Research Articles

Evaluation of required seismic gap between adjacent buildings in relation to the Egyptian Code

International seismic codes stipulate that adjacent buildings should be separated by a specified minimum distance, otherwise the pounding effect should be considered in the design. Recent researches proposed an alternative method (Double Difference Combination Rule) to estimate seismic gap between structures, as this method considers the cross relation of adjacent buildings behavior during earthquakes. Four different criteria were used to calculate the minimum separation distance using this method and results are compared to the international codes for five separation cases. These cases used four case study buildings classified by different heights, lateral load resisting systems and fundamental periods of vibrations to assess the consistency in results for the alternative methods. Non-linear analysis was performed to calculate the inelastic displacements of the four buildings, and the results were used to evaluate the relation between elastic and inelastic displacements due to the ductility of structural elements resisting seismic loads. A verification analysis was conducted to guarantee that the separation distance calculated is sufficient to avoid pounding. Results shows that the use of two out of the four studied methods yields separation distances smaller than that calculated by the code specified equations without under-estimating the minimum separation distance required to avoid pounding.

Upper crustal velocity and seismogenic environment of the <em>M</em>7.0 Jiuzhaigou earthquake region in Sichuan, China

On August 8, 2017, a magnitude 7.0 earthquake occurred in Jiuzhaigou County, Sichuan Province, China. The deep seismogenic environment and potential seismic risk in the eastern margin of Tibetan Plateau have once again attracted the close attention of seismologists and scholars at home and abroad. The post-earthquake scientific investigation could not identify noticeable surface rupture zones in the affected area; the complex tectonic background and the reason(s) for the frequent seismicity in the Jiuzhaigou earthquake region are unclear. In order to reveal the characteristics of the deep medium and the seismogenic environment of the <i>M</i>7.0 Jiuzhaigou earthquake region, and to interpret the tectonic background and genesis of the seismicity comprehensively, in this paper, we have reviewed all available observation data recorded by the regional digital seismic networks and large-scale, dense mobile seismic array (China Array) for the northern section of the North–South Seismic Belt around Jiuzhaigou earthquake region. Using double-difference seismic tomography method to invert the three-dimensional P-wave velocity structure characteristics of the upper crust around the Jiuzhaigou earthquake region, we have analyzed and discussed such scientific questions as the relationship between the velocity structure characteristics and seismicity in the Jiuzhaigou earthquake region, its deep tectonic environment, and the ongoing seismic risk in this region. We report that: the P-wave velocity structure of the upper crust around the Jiuzhaigoug earthquake region exhibits obvious lateral inhomogeneity; the distribution characteristics of the shallow P-wave velocity structure are closely related to surface geological structure and formation lithology; the <i>M</i>7.0 Jiuzhaigou earthquake sequence is closely related to the velocity structure of the upper crust; the mainshock of the <i>M</i>7.0 earthquake occurred in the upper crust; the inhomogeneous variation of the velocity structure of the Jiuzhaigou earthquake area and its surrounding medium appears to be the deep structural factor controlling the spatial distribution of the mainshock and its sequence. The 3D P-wave velocity structure also suggests that the crustal low-velocity layer of northeastern SGB (Songpan–Garzê Block) stretches into MSM (Minshan Mountain), and migrates to the northeast, but the tendency to emerge as a shallow layer is impeded by the high-velocity zone of Nanping Nappe tectonics and the Bikou Block. Our results reveal an uneven distribution of high- and low-velocity structures around the Tazang segment of the East Kunlun fault zone. Given that the rupture caused by the Jiuzhaigou earthquake has enhanced the stress fields at both ends of the seismogenic fault, it is very important to stay vigilant to possible seismic hazards in the large seismic gap at the Maqu–Maqên segment of the East Kunlun fault zone.

Acapulco earthquake struck the edge of a seismic gap

Acapulco earthquake struck the edge of a seismic gap

Active Subaquatic Fault Segments in Lake Iznik Along the Middle Strand of the North Anatolian Fault, NW Turkey

AbstractThe seismic activity of the middle strand of the North Anatolian Fault (MNAF), Northwestern Turkey, is debated because of its quiescence during the instrumental period, in contrast to a significant historical activity documented by several chronicles over the last two millennia. Here, we focus on Lake Iznik, bordered by the MNAF, to get a new insight into its long‐term seismicity and its tectonic setting. The study of lacustrine sediment cores reveals 14 earthquake‐induced turbidites since their ages correspond to seismic events during the past two millennia. Bathymetry and high‐resolution seismic reflection data allow to describe two hitherto unknown subaquatic active fault structures (the South Boyalica and Iznik faults) that belong to the MNAF system. Sediment cores sampled on both sides of the Iznik Fault document an event deposit and a sedimentary unit vertically offset of ~40 cm interpreted as the last rupture during the 1065 CE destructive earthquake. Older events are supposed on this fault more than thousand years ago. Further studies will help to estimate the horizontal co‐seismic offset of this oblique‐slip fault and the calendar of older ruptures. The current seismic gap of thousand years on this segment greatly increases the seismic hazard in this region and must be considered in the seismic risk assessment of the NAF system.

Exploratory study for strengthening education sectors for responding to complexities due to NATECH (Natural-Hazard Triggered Technological disasters) disasters

The city of Cilegon in Banten Province, Indonesia is selected as a site of this study. The city locates in the western edge of Java Islands and is known as one of the most famous and significant heavy industrial zones in Indonesia. Cilegon is potentially exposed both to natural and industrial hazards so that we can consider it as a suitable place for studying NATECH (NAtural-Hazard triggered TECHnological disasters) disaster situations. The Indonesian government indicates the presence of seismic gap in the Sunda Strait and the associated tsunami risk. Large-scale facilities of chemical, petrochemical, oil and gas industries stand in coastal areas in Cilegon. The industry and its surrounding communities can be affected by combination of the natural and industrial disasters. In Cilegon, we aim at strengthening capacity of the education section in the Cilegon city government and the school principals and teachers. Our preliminary implementation and survey reveal that knowledge and understanding of teachers are very limited. We will combine existing research findings from both of industrial accidents and tsunami, and develop educational materials.

Earthquake relocation to understand the megathrust segments along the Sumatran subduction zone

Historical seismicity shows the presence of mega-thrust segments along the Sumatran subduction zone that could generate large earthquakes. The segments include the Aceh-Andaman, Nias-Seumeuleu, Batu, Siberut, Mentawai-Pagai, Enggano, and Sunda Strait. Shallow and large earthquakes with magnitudes larger than 7.5 can occur along the segments thus trigger tsunamis. The accurate seismicity distribution along the subduction zone can be used to characterize the segments. The objective of the research is to precisely relocate the earthquakes in order to investigate the properties of the Sumatran subduction zone. Among more than 5000 preliminary located earthquakes occurring in 1980-2018 obtained from the Indonesian Agency for Geophysics (BMKG), only earthquakes with azimuthal gap angle less than 180 and recorded by at least 4 stations are used in the data analysis. We applied double difference method in order to relocate the seismic events. The result shows a zone with significantly less earthquakes along the subduction in West Aceh interpreted as a seismic gap zone. This zone is expected to accumulate energy which could be released in the form of a large earthquake. The new earthquake locations mimic shallower Sumatran subduction zone further north therefore closer to people inland. The closer earthquake the higher intensity of an earthquake felt by people which higher level of hazard. The pattern of the subduction zone derived from the relocated seismicity can be used as better source information for tsunami modeling.

Disparate deformation of the crust and upper mantle beneath the Doda-Kisthwar region, NW Himalaya

This study attempts to characterize the nature of seismicity, anisotropy and coherency of deformation in the crust and upper mantle beneath the Doda- Kisthwar region (DKR), Jammu, located in the Kashmir seismic gap of NW Himalaya. Location of earthquakes using local waveforms, and shear wave splitting in local and teleseismic waveforms recorded at 5 temporary stations, are performed for this purpose. The relocation of 890 earthquakes reveals two clusters along the NE and SW part (referred to as Kisthwar and Doda cluster respectively), which is attributed to the under-thrusting of the Indian plate and uplifting of Kisthwar Window respectively.The shear wave splitting analysis yielded a total of 47 local S and 11 XK(K)S splitting measurements. The corresponding Fast Polarization Azimuths (FPAs) show two distinct spatial patterns. In the first pattern, the FPAs are oriented along the NW direction, are perpendicular to the maximum horizontal stress, and are parallel to the structural trend as a result of oblique compression in the NW Himalaya. In the second pattern, the FPAs are oriented along the ENE-WSW direction and the corresponding delay times are found to be larger than those in the DKR. This could be because of localized deformation; the strike of fluid-filled fractures in the fault zone is also along the ENE-WSW direction, parallel to the course of the Chenab river. Thus, for both the trends, structure-induced anisotropy seems to be the most possible cause for the observed anisotropy. Further, the splitting parameters show a slight variation with depth for the respective orientation patterns.The delay times of the XK(K)S phases vary from 0.3 to 1.3 s, and cluster around 0.5 s, with the majority of FPAs, oriented along the ENE-WSW direction. This can be reconciled in terms of a combined effect of absolute plate motion (APM) related strain and finite strain induced by compression. The inconsistency in the upper crust and upper mantle anisotropy does not favour a coherently distributed lithospheric deformation in this segment of the NW Himalaya. The source of anisotropy in the upper crust is complex compared to that in the upper mantle.

Seismic gaps and intraplate seismicity around Rodrigues Ridge (Indian Ocean) from time domain array analysis

Abstract. Rodrigues Ridge connects the Réunion hotspot track with the Central Indian Ridge (CIR) and has been suggested to represent the surface expression of a sub-lithospheric flow channel. From global earthquake catalogues, the seismicity in the region has been associated mainly with events related to the fracture zones at the CIR. However, some segments of the CIR appear void of seismic events. Here, we report on the seismicity recorded at a temporary array of 10 seismic stations operating on Rodrigues Island from September 2014 to June 2016. The array analysis was performed in the time domain by time shifting and stacking the complete waveforms. Event distances were estimated based on a 1-D velocity model and the travel time differences between S and P wave arrivals. We detected and located 63 new events that were not reported by the global networks. Most of the events (51) are located off the CIR and can be classified as intraplate earthquakes. Local magnitudes varied between 1.6 and 3.7. Four seismic clusters were observed that occurred to the west of the spreading segment of the CIR. The Rodrigues Ridge appeared to be aseismic during the period of operation. The lack of seismic activity along both Rodrigues Ridge and the sections of the CIR to the east of Rodrigues may be explained by partially molten upper-mantle material, possibly in relation to the proposed material flow between the Réunion plume and the CIR.

Reflections on the Gap Hypothesis in the Immigration Policy of the Slovak Republic

Reflections on the Gap Hypothesis in the Immigration Policy of the Slovak Republic (Uvažovanie o gap hypotéze v slovenskej imigračnej politike) Journal Politické vedy has been released since 1998. The aim of the academically reviewed journal is to publish original articles of Slovak and foreign authors, concerning different fields of social science

Geodetic Observation of Seismic Cycles before, during, and after the 2020 Monte Cristo Range, Nevada Earthquake

AbstractThe 15 May 2020, M 6.5 Monte Cristo Range, Nevada earthquake (MCE) occurred inside the footprint of the semicontinuous MAGNET and continuous Network of the Americas Global Positioning System (GPS) networks, which provide precise geodetic coverage in the western Great basin. The event occurred in the White Mountain seismic gap between twentieth century events in the eastern central Walker Lane, on an east-northeast extension of faults in the Candelaria Hills. The earthquake precipitated a rapid and sustained GPS field response, which is providing data on the MCE pre-, co-, and postseismic deformation. The response was especially rapid owing to ∼1 dozen MAGNET stations immediately surrounding the epicenter being fortuitously occupied with receivers at event time. Modeling the coseismic displacements suggests that the MCE offset was ∼1 m, greater than the individual observations of surface rupture, but consistent with the seismic moment. Although the epicenter is separated from most of the observed surface rupture by ∼10 km, the slip plane inferred from the GPS data spans the gap, suggesting deep slip continuity that tapered toward the surface, making the event partially blind. However, the range of magnitudes estimated from geologic, geodetic, and seismic data overlap in the range of Mw 6.3–6.4. Postseismic displacement over several months occurred in directions aligned with the coseismic displacement, suggesting afterslip of over 9% of the coseismic displacement, too large to be explained by aftershock seismicity, suggesting that most postseismic deformation was aseismic. The interseismic direction of no-length change was very closely aligned to the MCE slip azimuth, as expected for a strike-slip event. This alignment is sensitive to transient postseismic viscoelastic deformation from previous earthquakes in the western Great basin, which may have temporarily improved the alignment. Thus, these viscoelastic transients may have created conditions favoring the slip to occur on the MCE fault.

The Campotosto linkage fault zone between the 2009 and 2016 seismic sequences of central Italy: Implications for seismic hazard analysis

In the last decade central Italy was struck by devastating seismic sequences resulting in hundreds of casualties (i.e., 2009-L′Aquila moment magnitude [Mw] = 6.3, and 2016-Amatrice-Visso-Norcia Mw max = 6.5). These seismic events were caused by two NW-SE−striking, SW-dipping, seismogenic normal faults that were modeled based on the available focal mechanisms and the seismic moment computed during the relative mainshocks. The seismogenic faults responsible for the 2009-L′Aquila Mw = 6.3 (Paganica Fault—PF) and 2016-Amatrice-Visso-Norcia Mw max = 6.5 (Monte Vettore Fault—MVF) are right-stepping with a negative overlap (i.e., underlap) located at the surface in the Campotosto area. This latter was affected by seismic swarms with magnitude ranging from 5.0 to 5.5 during the 2009 seismic sequence and then in 2017 (i.e., a few months later than the mainshocks related with the 2016 seismic sequence). In this paper, the seismogenic faults related to the main seismic events that occurred in the Campotosto Seismic Zone (CSZ) were modeled and interpreted as a linkage fault zone between the PF and MVF interacting seismogenic faults. Based on the underlap dimension, the seismogenic potential of the CSZ is in the order of Mw = 6.0, even in the case that all the faults belonging to the zone were activated simultaneously. This has important implications for seismic hazard assessment in an area dominated by the occurrence of a major NW-SE−striking extensional structure, i.e., the Monte Gorzano Fault (MGF). Mainly due to its geomorphologic expression, this fault has been considered as an active and silent structure (therefore representing a seismic gap) able to generate an earthquake of Mw max = 6.5−7.0. However, the geological evidence provided with this study suggests that the MGF is of early (i.e., pre- to syn-thrusting) origin. Therefore, the evaluation of the seismic hazard in the Campotosto area should not be based on the geometrical characteristics of the outcropping MGF. This also generates substantial issues with earthquake geological studies carried out prior to the recent seismic events in central Italy. More in general, the 4-D high-resolution image of a crustal volume hosting an active linkage zone between two large seismogenic structures provides new insights into the behavior of interacting faults in the incipient stages of connection.

Experimental study of the seismic performance of plasterboard partition walls with seismic gaps

It is now widely recognized that the performance of non-structural elements is crucial to the performance of building systems during earthquakes. Field surveys and experimental studies have shown that light steel or timber framed plasterboard partition walls are particularly vulnerable. The objective of this study is to investigate the seismic performance of a novel seismic gap partition system with angled return walls under quasi-static cyclic loading applied obliquely and to investigate the benefits of using acrylic gap-filler in the seismic gaps. Two specimens were tested: a steel stud specimen and a timber stud specimen. Observed drift capacities were significantly greater than traditional plasterboard partition systems. Equations were used to predict the drift at which damage state 1 (DS1) and damage state 2 (DS2) would initiate. The equation used to estimate the drift at the onset of DS1 accurately predicted the onset of plaster cracking but overestimated the drift at which the gap filling material was damaged. The equation used to predict the onset of DS2 provided a lower bound for both specimens and also when used to predict results of previous experimental tests on seismic gap systems. The gap-filling material reduced the drift at the onset of DS1, however, it had a beneficial effect on the re-centring behaviour of the linings. Out-of-plane displacements and return wall configuration did not appear to significantly impact the onset of plaster cracking in the specimens.

A Recent Tear in Subducting Plate Explains Seismicity and Upper Mantle Structure of Southern Costa Rica

AbstractPast studies of southern Costa Rica have generated a multitude of tectonic scenarios to account for different data sets. Flat slabs, detached slabs, and slab windows have been proposed to address the uplift of the Cordillera de Talamanca (CT), cessation of volcanism, and absence of deep seismicity beneath southern Costa Rica. In this study, we investigate the crust and the upper mantle along the southwest flank of the CT using the receiver function methodology. We observe two regional positive P‐to‐S converted pulses at delay times of ∼2–4 s and ∼5–8 s. The first likely represents a gradational crust‐mantle boundary of the upper plate. The second represents a similar impedance increase ∼50–60 km deep that extends from central Costa Rica to Panama. Compared to well‐located seismicity, this boundary is offset to the NE from the Cocos plate Benioff zone beneath northern CT, and remains observable through a gap in seismicity farther to the southeast. This offset makes it difficult to interpret this feature as related to the presently subducting lithosphere. Instead, we propose that the 50–60 km deep boundary marks the Moho of a lithospheric fragment left behind under the CT in the course of Panama Triple Junction migration through Costa Rica over the last 10 Ma. Our interpretation accounts for the geophysical, geochemical, structural, and geomorphic observations in the literature explaining the complex geodynamic scenario observed in southern Costa Rica.

First Results on the Mw=6.9 Samos Earthquake of 30 October 2020

On 30 October 2020 11:51 UTC, a Mw=6.9 earthquake struck the offshore region north of Samos Island, Greece, in the Gulf of Ephesos/Kuşadasi, causing two fatalities and 19 minor injuries at Samos Island, as well as 115 casualties and over 1,030 injuries in Western Turkey. Preliminary results indicate that the mainshock occurred on a north-dipping normal fault, with a focal mechanism of 270º/50º/-81º. The selection of the fault plane is supported by evidence of uplift at western Samos and over 10 cm of subsidence at the northernmost edge of the central part of the island. The distribution of relocated hypocenters shows clustering of events, east of the mainshock’s epicenter, where most major aftershocks have occurred. To the west, a smaller group of aftershocks is observed, separated by a spatial gap in seismicity. The latter is likely related to the region of the fault plane where most of the co-seismic slip occurred, with Coulomb stress-transfer towards the western and eastern margins of the rupture triggering aftershock activity. The apparent complexity of the mainshock’s source time function, supported by preliminary results, could indicate the rupture of more than one structures. This could explain the relatively weak magnitude of the largest aftershock (Mw=5.0). The mainshock caused damage mainly to non-engineered constructions, i.e. old residential buildings, churches and monuments in Samos Island, and minor damage to the majority of the building stock of the island built according to the National Seismic Code. On the other hand, it caused severe damage at Izmir, especially to high-rise buildings. The mainshock also triggered a small tsunami that reached heights of over 1 m, mainly affecting the Turkish coast.

Merzifon–Esençay splay fault within the North Anatolian Fault system: segmentation and timing of the last two surface faulting events on Esençay segment

North Anatolian Fault (NAF) as a seismically active intracontinental plate boundary is characterized by splay faults in a half fishbone geometry, reaching into the Anatolian plate. Recent crustal deformations within Central Anatolia Tectonic Province are accommodated by dextral and sinistral strike-slip splay fault systems. Sinistral splays extend conjugate to the NAF and subparallel to the East Anatolian Fault (EAF), while the dextral splays are subparallel to the NAF. Sungurlu–Ezinepazar (SEF) and Merzifon–Esencay (MEF) faults are two major dextral splays bifurcating from Niksar pull-apart basin, which distinguish eastern and central NAF. Geodetic and geological data suggest a total of 3 mm/year slip rate along these splays in a setting of slip partitioning with the main strand of the NAF. These two splays undertake 12–13% of the lateral motion within a broad deformation zone of the NAF where the MEF accommodates 1/3 of this amount. 227 km-long MEF is divided into six fault segments, which are separated from each other’s by releasing and restraining jogs. Cumulative offsets up to 3.0 km on Kizilirmak River valley and tributaries of Yesilirmak River since latest Pliocene-Early Pleistocene (~ 3 Ma) suggest an approximately 1 mm/year long-term geological slip rate on the MEF. Paleoseismological findings from Esencay segment reveal two discrete surface faulting events within the last 7 ka with a return period of maximum 2200 and minimum 1320 years. The lapse time since the last event is about 3700 years. This implies ~ 3.7 m of strain accumulation on the Esencay segment for present. The segments have the potential to produce induvial earthquakes with magnitudes varying between Mw 6.8 and Mw 7.2. Existing information imply that major fault splays have the potential to produce multi-segment large earthquakes within the NAF zone in addition to well-known Yedisu and Central Marmara seismic gaps.

Large earthquakes in the Tehuantepec subduction zone: evidence of a locked plate interface and large-scale deformation of the slab

The Tehuantepec subduction zone was identified as a seismic gap by several authors. The presence of three large earthquakes at the turn of the twentieth century, in temporal and spatial proximity, poses questions on the extent of the seismic gap and on the type of tectonic deformation in this region. On 19 April 1902, a large earthquake occurred in Guatemala. The macroseismic data and recent relocations suggest that it is not a subduction event but an intraplate earthquake within the subducted Cocos plate. The recent relocations and the macroseismic data of the 23 September 1902 earthquake, which is frequently interpreted as an interplate subduction event, show that it is an intermediate-depth earthquake located inland in central Mexico. The 14 January 1903 earthquake, located in the Gulf of Tehuantepec, may be interpreted as an intraplate event, similar to the 8 September 2017 earthquake (Mw 8.2) or a subduction earthquake. Thus, there is no clear evidence of large subduction earthquakes (Mw > 7) in Tehuantepec at least in the last 250 years. Geodetic data suggest that the subduction zone is highly coupled and, therefore, a considerable amount of plate motion has not been released. The length of the presumed seismic gap is equivalent to a Mw ~ 8.5 earthquake. In contrast, the September 1902 (Mw 7.8), 1903 (Mw 7.4), 1931 (Mw 7.8), 1999 (Mw 7.5) and the great 8 September 2017 events (Mw 8.2) are all down-dip tensional earthquakes in the slab, reflecting a complex state of stress in the downgoing Cocos plate. These frequent and large tensional earthquakes may reflect a large-scale deformation of the slab that locked at the plate interface is under tensional stress under its own gravitational weight. As a result, seismic hazard in the Isthmus of Tehuantepec stems from both subduction and intraplate earthquakes.

Kinematics and Dynamics of the 24 January 2020 Mw 6.7 Elazig, Turkey Earthquake

AbstractWe determine rupture kinematics of the 2020 Mw 6.7 Elazig, Turkey earthquake from joint inversion of interferometric synthetic aperture radar (InSAR) measurements, regional 1 Hz Global Navigation Satellite System (GNSS), strong motion, and teleseismic waveforms, and we also use dynamic modeling to assess the faulting properties to explain the observed kinematics. Our work shows that this event predominantly ruptured unilaterally toward the SW along the East Anatolian Fault Zone at a speed as slow as 2.0 km/s for ~20 s, and three main asperities are formed with a depth ranging from 20 km to the surface, but the surface rupture seems negligible. Besides, the dynamic model reveals an initial heterogeneous stress distribution with variations up to 30 MPa, which has been probably built up during the interseismic period. While this event does not seem to promote the failure of Pazarcık seismic gap, it remains elusive to evaluate the disturbed seismic potential between Elazig and Bingol regions.

Crustal deformation rates in Kashmir valley and adjoining regions from continuous GPS measurements from 2008 to 2019

We present GPS velocities in Kashmir valley and adjoining regions from continuous Global Positioning System (cGPS) network during 2008 to 2019. Results indicate total arc normal shortening rates of ~ 14 mm/year across this transect of Himalaya that is comparable to the rates of ~ 10 to 20 mm/year reported else-where in the 2500 km Himalaya Arc. For the first time in Himalayas, arc-parallel extension rate of ~ 7 mm/year was recorded in the Kashmir valley, pointing to oblique deformation. Inverse modeling of the contemporary deformation rates in Kashmir valley indicate oblique slip of ~ 16 mm/year along the decollement with locking depth of ~ 15 km and width of ~ 145 km. This result is consistent with the recorded micro-seismicity and low velocity layer at a depth of 12 to 16 km beneath the Kashmir valley obtained from collocated broadband seismic network. Geodetic strain rates are consistent with the dislocation model and micro-seismic activity, with high strain accumulation (~ 7e−08 maximum compression) to the north of Kashmir valley and south of Zanskar ranges. Assuming the stored energy was fully released during 1555 earthquake, high geodetic strain rate since then and observed micro-seismicity point to probable future large earthquakes of Mw ~ 7.7 in Kashmir seismic gap.

Geochemical Characteristics of Soil Gas and Strong Seismic Hazard Potential in the Liupanshan Fault Zone (LPSFZ)

Eight soil gas measurements were performed in the Liupanshan fault zone (LPSFZ) to observe the concentration and flux of soil gas radon (Rn) and CO2 in October 2017 and October 2018. By combining the historical strong earthquake background and modern seismic activity of the fault zone, the relation between the geochemical distribution characteristics of soil gas and the seismicity of the fault zone was studied herein. Furthermore, the strong seismic hazard potential of the fault zone was discussed. Results show that the concentration of soil gas Rn and CO2 considerably varies in the northern segment of the LPSFZ and is relatively stable in the southern segment. The spatial distribution of the concentration intensity and flux is strong in the north and weak in the south. However, the southern segment of the LPSFZ has a seismic gap that has not been ruptured by strong earthquakes with Ms ≥ 6.5 for the last 1400 years, whereas the seismic activity in the northern segment is relatively frequent, indicating that the fault zone locking degree of the southern segment is higher than that of the northern segment. This observation is completely consistent with the geochemical characteristic distribution of soil gas. Therefore, the southern segment of the LPSFZ should be considered a hazardous segment, where major or strong earthquakes can occur in the future.

Seismic structure and tectonics of the continental wedge overlying the source region of the Iquique Mw8.1 2014 earthquake

On April 1, 2014, a large earthquake (Mw = 8.1) ruptured the central part of a historic seismic gap in northern Chile. In order to study the relationship between the co-seismic rupture characteristics and the crustal structure of the subduction zone, we processed a trench-perpendicular seismic reflection profile acquired across the zone of maximum slip and generated a P-wave velocity model. The results show a frontal prism in the continental wedge characterized by low velocities that increase rapidly towards the shore and acted as a barrier for trench-ward propagation of aftershocks. Landward, a transition zone with increasing upper crust velocity (4–5 km/s) concentrates most of the aftershocks. In addition, a trench-ward dipping set of fault zones is observed along the continental wedge associated to the Iquique forearc basin formation (1.5 km thick at the depocenter on this profile). We identify three stratigraphic units within the basin. A landward tilt and thickness increase is detected in each stratigraphic unit, along with growth strata and domino structures, suggesting landward migration of syn-extensional deformation in response to basal subduction erosion. By extrapolating our results to the plate boundary and based on published focal mechanisms of intra-crustal seismicity, we find a strong spatial correlation between the Iquique basin and the highest slip area for the 2014 earthquake, suggesting long-term extensional deformation due to coseismic tensional stresses.