The influence of fluids in the unusually high-rate seismicity in the Ometepec segment of the Mexican subduction zone

2021 ◽  
Author(s):  
D Legrand ◽  
A Iglesias ◽  
S K Singh ◽  
V Cruz-Atienza ◽  
C Yoon ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Temporal Distribution ◽  
Aftershock Sequence ◽  
High Rate ◽  
Earth Tides ◽  
P Value ◽  
Plate Interface ◽  
Flow Measurements ◽  
Slow Slip Events ◽  
Mexican Subduction Zone

Summary The rate of earthquakes with magnitudes Mw ≤ 7.5 in the Ometepec segment of the Mexican subduction zone is relatively high as compared to the neighboring regions of Oaxaca and Guerrero. Although the reason is not well understood, it has been reported that these earthquakes give rise to a large number of aftershocks. Our study of the aftershock sequence of the 2012 Mw7.4 Ometepec thrust earthquake suggests that it is most likely due to two dominant factors: (1) The presence of an anomalously high quantity of over-pressured fluids near the plate interface, and (2) the roughness of the plate interface. More than 5,400 aftershocks were manually detected during the first ten days following the 2012 earthquake. Locations were obtained for 2,419 events (with duration magnitudes Md ≥ 1.5). This is clearly an unusually high number of aftershocks for an earthquake of this magnitude. Furthermore, we generated a more complete catalog, using an unsupervised fingerprint technique, to detect more smaller events (15,593 within one month following the mainshock). For this catalog, a high b-value of 1.50 ± 0.10 suggests the presence of fluid release during the aftershock sequence. A low p-value (0.37 ± 0.12) of the Omori law reveals a slow decaying aftershock sequence. The temporal-distribution of aftershocks shows peaks of activity with two dominant periods of 12h and 24h that correlate with the Earth tides. To explain these observations, we suggest that the 2012 aftershock sequence is associated with the presence of over-pressured fluids and/or a heterogeneous and irregular plate interface related to the subduction of the neighboring seamounts. High fluid content has independently been inferred by magneto-telluric surveys and deduced from heat flow measurements in the region. The presence of fluids in the region has also been proposed to explain the occurrence of slow slip events, low frequency earthquakes, and tectonic tremors.

scholarly journals Earthquake swarms and slow slip on a sliver fault in the Mexican subduction zone

2019 ◽  
Vol 116 (15) ◽  
pp. 7198-7206 ◽  
Author(s):  
Shannon L. Fasola ◽  
Michael R. Brudzinski ◽  
Stephen G. Holtkamp ◽  
Shannon E. Graham ◽  
Enrique Cabral-Cano
Keyword(s):  
Subduction Zone ◽  
Local Network ◽  
Seismogenic Zone ◽  
Slow Slip ◽  
Plate Interface ◽  
Slow Slip Events ◽  
Parallel Motion ◽  
Oblique Convergence ◽  
Seismicity Catalog ◽  
Mexican Subduction Zone

The Mexican subduction zone is an ideal location for studying subduction processes due to the short trench-to-coast distances that bring broad portions of the seismogenic and transition zones of the plate interface inland. Using a recently generated seismicity catalog from a local network in Oaxaca, we identified 20 swarms of earthquakes (M < 5) from 2006 to 2012. Swarms outline what appears to be a steeply dipping structure in the overriding plate, indicative of an origin other than the plate interface. This steeply dipping structure corresponds to the northern boundary of the Xolapa terrane. In addition, we observed an interesting characteristic of slow slip events (SSEs) where they showed a shift from trenchward motion toward an along-strike direction at coastal GPS sites. A majority of the swarms were found to correspond in time to the along-strike shift. We propose that swarms and SSEs are occurring on a sliver fault that allows the oblique convergence to be partitioned into trench-perpendicular motion on the subduction interface and trench-parallel motion on the sliver fault. The resistivity structure surrounding the sliver fault suggests that SSEs and swarms of earthquakes occur due to high fluid content in the fault zone. We propose that the sliver fault provides a natural pathway for buoyant fluids attempting to migrate upward after being released from the downgoing plate. Thus, sliver faults could be responsible for the downdip end of the seismogenic zone by creating drier conditions on the subduction interface trenchward of the sliver fault, promoting fast-slip seismogenic rupture behavior.

Systematic characterization of slow slip events along the Mexican subduction zone from 2000 to 2019

2020 ◽  
Author(s):  
Mathilde Radiguet ◽  
Ekaterina Kazachkina ◽  
Louise Maubant ◽  
Nathalie Cotte ◽  
Vladimir Kostoglodov ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Scaling Laws ◽  
Temporal Evolution ◽  
Seismic Gap ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Grace Data ◽  
Spatio Temporal ◽  
Mexican Subduction Zone

&lt;p&gt;Slow slip events (SSEs) represent a significant mechanism of strain release along several subduction zones, and understanding their occurrence and relations with major earthquake asperities is essential for a comprehensive understanding of the seismic cycle. Here, we focus on the Mexican subduction zone, characterized by the occurrence of recurrent large slow slip events (SSEs), both in the Guerrero region, where the SSEs are among the largest observed worldwide, and in the Oaxaca region, where smaller, more frequent SSEs occur. Up to now, most slow slip studies in the Mexican subduction zone focused either on the detailed analysis of a single event, were limited to a small area (Guerrero or Oaxaca), or were limited to data before 2012 [e.g.1-4]. In this study, our aim is to build an updated and consistent catalog of major slow slip events in the Guerrero-Oaxaca region.&lt;/p&gt;&lt;p&gt;We use an approach similar to Michel et al. 2018 [5]. We analyze the GPS time series from 2000 to 2019 using Independent Component Analysis (ICA), in order to separate temporally varying sources of different origins (seasonal signals, SSEs and afterslip of major earthquakes). We are able to isolate a component corresponding to seasonal loading, which matches the temporal evolution of displacement modeled from the GRACE data. The sources (independent components) identified as tectonic sources of deep origin are inverted for slip on the subduction interface. We thus obtain a model of the spatio-temporal evolution of aseismic slip on the subduction interface over 19 years, from which we can isolate around 30 individual slow slip events of M&lt;sub&gt;w &lt;/sub&gt;&gt; 6.2.&lt;/p&gt;&lt;p&gt;&amp;#160;The obtained catalog is coherent with previous studies (in terms of number of events detected, magnitude and duration) which validates the methodology. The observed moment-duration scaling is close to M&lt;sub&gt;0&lt;/sub&gt;~T&lt;sup&gt;3 &lt;/sup&gt;as recently suggested by Michel [6] for Cascadia SSEs, and our study extends the range of magnitude considered in their analysis. Finally, we also investigate the spatio-temporal relations between the SSEs occurring in the adjacent regions of Guerrero and Oaxaca, and their interaction with local and distant earthquakes.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;ol&gt;&lt;li&gt;Kostoglodov, V. et al. A large silent earthquake in the Guerrero seismic gap, Mexico. Geophys. Res. Lett &lt;strong&gt;30&lt;/strong&gt;, 1807 (2003).&lt;/li&gt; &lt;li&gt;Graham, S. et al. Slow Slip History for the Mexico Subduction Zone: 2005 Through 2011. Pure and Applied Geophysics 1&amp;#8211;21 (2015). doi:10.1007/s00024-015-1211-x&lt;/li&gt; &lt;li&gt;Larson, K. M., Kostoglodov, V. &amp; Shin&amp;#8217;ichi Miyazaki, J. A. S. The 2006 aseismic slow slip event in Guerrero, Mexico: New results from GPS. Geophys. Res. Lett. &lt;strong&gt;34&lt;/strong&gt;, L13309 (2007).&lt;/li&gt; &lt;li&gt;Radiguet, M. et al. Slow slip events and strain accumulation in the Guerrero gap, Mexico. J. Geophys. Res. &lt;strong&gt;117&lt;/strong&gt;, B04305 (2012).&lt;/li&gt; &lt;li&gt;Michel, S., Gualandi, A. &amp; Avouac, J.-P. Interseismic Coupling and Slow Slip Events on the Cascadia Megathrust. Pure Appl. Geophys. (2018). doi:10.1007/s00024-018-1991-x&lt;/li&gt; &lt;li&gt;Michel, S., Gualandi, A. &amp; Avouac, J. Similar scaling laws for earthquakes and Cascadia slow-slip events. Nature &lt;strong&gt;574, &lt;/strong&gt;522&amp;#8211;526 (2019) doi:10.1038/s41586-019-1673-6&lt;/li&gt; &lt;/ol&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

scholarly journals Slow slip source characterized by lithological and geometric heterogeneity

2020 ◽  
Vol 6 (13) ◽  
pp. eaay3314 ◽  
Author(s):  
Philip M. Barnes ◽  
Laura M. Wallace ◽  
Demian M. Saffer ◽  
Rebecca E. Bell ◽  
Michael B. Underwood ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Source Region ◽  
Significant Proportion ◽  
Plate Motion ◽  
Direct Access ◽  
Slow Slip ◽  
Plate Interface ◽  
Slow Slip Events ◽  
Geophysical Imaging

Slow slip events (SSEs) accommodate a significant proportion of tectonic plate motion at subduction zones, yet little is known about the faults that actually host them. The shallow depth (<2 km) of well-documented SSEs at the Hikurangi subduction zone offshore New Zealand offers a unique opportunity to link geophysical imaging of the subduction zone with direct access to incoming material that represents the megathrust fault rocks hosting slow slip. Two recent International Ocean Discovery Program Expeditions sampled this incoming material before it is entrained immediately down-dip along the shallow plate interface. Drilling results, tied to regional seismic reflection images, reveal heterogeneous lithologies with highly variable physical properties entering the SSE source region. These observations suggest that SSEs and associated slow earthquake phenomena are promoted by lithological, mechanical, and frictional heterogeneity within the fault zone, enhanced by geometric complexity associated with subduction of rough crust.

scholarly journals Unraveling the Origin of Slow Earthquakes

Eos ◽  
2019 ◽  
Vol 100 ◽  
Author(s):  
Terri Cook
Keyword(s):  
Physical Properties ◽  
Subduction Zone ◽  
Slow Slip ◽  
Tectonic Plate ◽  
Plate Interface ◽  
Change Over Time ◽  
Slow Slip Events ◽  
Slow Earthquakes ◽  
Over Time

Different nucleation styles detected in five slow-slip events in the same area of Japan’s Ryukyu subduction zone suggest the physical properties along this tectonic plate interface change over time.

scholarly journals Tectonic tremors in the Northern Mexican subduction zone remotely triggered by the 2017 Mw8.2 Tehuantepec earthquake

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Masatoshi Miyazawa ◽  
Miguel Ángel Santoyo
Keyword(s):  
Subduction Zone ◽  
Dynamic Strain ◽  
Plate Boundaries ◽  
Maximum Magnitude ◽  
Slab Geometry ◽  
Plate Interface ◽  
Wavefield Simulation ◽  
Stress Changes ◽  
Triggered Tremor ◽  
Mexican Subduction Zone

AbstractSurface waves from the 2017 Mw8.2 Tehuantepec earthquake remotely triggered tectonic tremors in the Jalisco region, approximately 1000 km WNW in the northern Mexican subduction zone. This is the first observation of tremor triggering in this region and one of the largest known examples of a triggered tremor in the world. Although prior studies have found tectonic tremors triggered by teleseismic waves in subduction zones and plate boundaries, further investigation of tremor triggering is crucially important for understanding the causative mechanism. We calculate the stress and strain changes across the three-dimensional plate interface attributable to seismic waves from the earthquake by full wavefield simulation. The maximum magnitude of the dynamic strain tensor eigenvalues on the plate interface, where tremors likely occur, is approximately 10–6. The subducting slab geometry effectively amplifies triggering waves. The triggering Coulomb failure stress changes resolved for a thrust fault plane consistent with the geometry are estimated to be approximately 10–40 kPa. The relationship between the triggering stress and triggered tremor amplitude may indicate that the aσ of the rate–state-dependent friction law is 10–100 kPa.

scholarly journals Tectonic Tremors in the Northern Mexican Subduction Zone Remotely Triggered by the 2017 Mw8.2 Tehuantepec Earthquake

2020 ◽  
Author(s):  
Masatoshi Miyazawa ◽  
Miguel Ángel Santoyo
Keyword(s):  
Subduction Zone ◽  
Dynamic Strain ◽  
Plate Boundaries ◽  
Maximum Magnitude ◽  
Slab Geometry ◽  
Plate Interface ◽  
Wavefield Simulation ◽  
Stress Changes ◽  
Triggered Tremor ◽  
Mexican Subduction Zone

Abstract Surface waves from the 2017 Mw8.2 Tehuantepec earthquake remotely triggered tectonic tremors in the Jalisco region, approximately 1000 km WNW in the northern Mexican subduction zone. This is the first observation of tremor triggering in this region and one of the largest known examples of triggered tremor in the world. While prior studies found tectonic tremors triggered by teleseismic waves in subduction zones and plate boundaries, further investigation of tremor triggering is crucially important for understanding the causative mechanism. We calculate the stress and strain changes across the three-dimensional plate interface attributable to seismic waves from the earthquake by full wavefield simulation. The maximum magnitude of the dynamic strain tensor eigenvalues on the plate interface, where tremors likely occur, is approximately 10-6. The subducting slab geometry effectively amplifies triggering waves. The triggering Coulomb failure stress changes resolved for a thrust fault plane consistent with the geometry are estimated at approximately 10-40 kPa. The relationship between the triggering stress and triggered tremor amplitude may indicate that the aσ of the rate-state-dependent friction law is 10 to 100 kPa.

scholarly journals Tectonic Tremors in the Northern Mexican Subduction Zone Remotely Triggered by the 2017 Mw8.2 Tehuantepec Earthquake

2020 ◽  
Author(s):  
Masatoshi Miyazawa ◽  
Miguel Ángel Santoyo
Keyword(s):  
Subduction Zone ◽  
Dynamic Strain ◽  
Plate Boundaries ◽  
Maximum Magnitude ◽  
Slab Geometry ◽  
Plate Interface ◽  
Wavefield Simulation ◽  
Stress Changes ◽  
Triggered Tremor ◽  
Mexican Subduction Zone

Abstract Surface waves from the 2017 Mw8.2 Tehuantepec earthquake remotely triggered tectonic tremors in the Jalisco region, approximately 1000 km WNW in the northern Mexican subduction zone. This is the first observation of tremor triggering in this region and one of the largest known examples of a triggered tremor in the world. Although prior studies have found tectonic tremors triggered by teleseismic waves in subduction zones and plate boundaries, further investigation of tremor triggering is crucially important for understanding the causative mechanism. We calculate the stress and strain changes across the three-dimensional plate interface attributable to seismic waves from the earthquake by full wavefield simulation. The maximum magnitude of the dynamic strain tensor eigenvalues on the plate interface, where tremors likely occur, is approximately 10 -6 . The subducting slab geometry effectively amplifies triggering waves. The triggering Coulomb failure stress changes resolved for a thrust fault plane consistent with the geometry are estimated to be approximately 10-40 kPa. The relationship between the triggering stress and triggered tremor amplitude may indicate that the [[EQUATION]] of the rate-state-dependent friction law is 10 to 100 kPa.

scholarly journals Smoking habits among medical students: a survey at the University of Prishtina Faculty of Medicine

2018 ◽  
Vol 6 (1) ◽  
pp. 18-20 ◽  
Author(s):  
Albina Fejza ◽  
Fatjeta Maraj ◽  
Hajrullah Fejza
Keyword(s):  
Medical Students ◽  
Role Models ◽  
High Rate ◽  
Smoking Habits ◽  
P Value ◽  
Student Survey ◽  
Public Places ◽  
Exact Test ◽  
The University ◽  
Medical University

Background: Smoking is a common habit among the population in Kosovo. In the country, smoking occurs in public places, health and educational institutions despite being prohibited by law. Our objective was to describe smoking habits, knowledge and attitudes among medical students from all departments in the University of Prishtina, Faculty of Medicine. Methods: The present study followed the Global Health Professions Student Survey (GHPSS) standardized methodology including data processing procedures. A self-administered questionnaire used was derived from the GHPSS. A total of 600 students were invited in the study while 470 returned questionnaires and participated in the study. Descriptive statistics were used to present the data. The Fisher’s exact test was used to test the significance and a p-value<0.05 was considered significant. Results: The prevalence rate of smoking among students was 16.9% (95% CI 13.2-20). Current smokers were 79 students, 28.2 % males, and 7.7 % females. The study showed that 55.5% of students smoke less than a pack of cigarettes per day. Almost half of them (47.6%) who smoke reported to have a smoker inside the family.  This study also revealed that 74.7% of respondents smoke in the presence of non-smokers on daily bases. Conclusion: Despite threating their own health, smokers also cause noxiousness to the society and medical students should be role models for the others by not smoking. Even though the percentage doesn’t show a high rate of smokers in Medical University of Prishtina, still we need to pay attention to bad smoking habits and try to lower even more the percentage of smokers.

scholarly journals Young people's lifestyle and frequency of physical activity – an original study

2020 ◽  
Vol 66 (4) ◽  
pp. 54-60
Author(s):  
Barbara Janota ◽  
Elżbieta Szczepańska ◽  
Karolina Janion
Keyword(s):  
Physical Activity ◽  
Positive Impact ◽  
High Rate ◽  
P Value ◽  
Daily Consumption ◽  
Unhealthy Lifestyle ◽  
School Students ◽  
Group 3 ◽  
Group 2 ◽  
Group 1

Abstract Introduction A healthy lifestyle, including healthy eating, frequent physical activity, abstention from recreational substances, appropriate amounts of sleep and restricted amounts of television and computer time have a positive impact on the development and health of adolescents. The aim of the study was to assess selected aspects of adolescent lifestyle with a focus on rates of physical activity. Materials and methods The study material included a questionnaire completed by 304 secondary school students. The answers were analysed with respect to the physical activity of the respondents and then grouped accordingly: group 1 consisted of respondents with a low rate of physical activity, group 2 with a moderate rate of physical activity and group 3 with a high rate of physical activity. Differences in the the percentages of healthy behaviour the groups engaged in was assessed using the Kruskal–Wallis ANOVA on ranks test. Post hoc, a 2-way test with Bonferroni correction was performed. A p value of <0.05 was considered statistically significant for all analyses. Results The recommended number of 4–5 meals a day is consumed mostly by individuals from group 2 (52.94%) and to the least extent by those in group 1 (47.17%). The recommended daily consumption of fruit is mostly reported by respondents from group 3 (39.34%) and the least, by those from group 1 (26.42%). Subjects from group 2 are least likely to drink alcohol, which is harmful for one's health (26.47%); this group also includes the largest number of individuals who do not smoke cigarettes (69.12%). The most favorable behaviour with regards to sleep is displayed by subjects from group 3, in which 10.38% of participants slept for the recommended 8–10 h a day. Conclusions The majority of adolescents, regardless of the frequency of physical activity they undertook, had an unhealthy lifestyle. The most favourable lifestyle was led by subjects who performed physical activity between once a week and a few times a month.

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