Egyptian National Seismic Network Research Articles

Characterizing Egyptian National Seismic Network station sites using genetic optimization for microtremor data inversion

Characterizing Egyptian National Seismic Network station sites using genetic optimization for microtremor data inversion

Prototype Implementation of a Digitizer for Earthquake Monitoring System.

A digitizer is considered one of the fundamental components of an earthquake monitoring system. In this paper, we design and implement a high accuracy seismic digitizer. The implemented digitizer consists of several blocks, i.e., the analog-to-digital converter (ADC), GPS receiver, and microprocessor. Three finite impulse response (FIR) filters are used to decimate the sampling rate of the input seismic data according to user needs. A graphical user interface (GUI) has been designed for enabling the user to monitor the seismic waveform in real time, and process and adjust the parameters of the acquisition unit. The system casing is designed to resist harsh conditions of the environment. The prototype can represent the three component sensors data in the standard MiniSEED format. The digitizer stream seismic data from the remote station to the main center is based on TCP/IP connection. This protocol ensures data transmission without any losses as long as the data still exist in the ring buffer. The prototype was calibrated by real field testing. The prototype digitizer is integrated with the Egyptian National Seismic Network (ENSN), where a commercial instrument is already installed. Case studies shows that, for the same event, the prototype station improves the solution of the ENSN by giving accurate timing and seismic event parameters. Field test results shows that the event arrival time and the amplitude are approximately the same between the prototype digitizer and the calibrated digitizer. Furthermore, the frequency contents are similar between the two digitizers. Therefore, the prototype digitizer captures the main seismic parameters accurately, irrespective of noise existence.

Enhancing analyst decisions for seismic source discrimination with an optimized learning model

Sustainable development in urban areas requires a wide variety of current and theme-based information for efficient management and planning. In addition, researching the spatial distribution of earthquake (EQ) clusters is an important step in reducing seismic risks and EQ losses through better assessment of seismic hazards, therefore it is desirable to acquire an uncontaminated database of seismic activity. Quarry blasts (QBs) conducted over the mapped area have tainted the seismicity inventory in the northwestern region of Egypt, which is the focus of this paper. Separating these QBs from the EQs is hence preferable for accurate seismicity and risk assessments. Consequently, we present a highly effective ML model for cleaning up the seismicity database, allowing for the accurate delineation of EQ clusters using data from a single seismic station, “AYT”, which is part of the Egyptian National Seismic Network. The magnitudes ≤3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\le 3$$\\end{document} that are very uncertain as EQs or QBs and need a significant amount of time to analyze are the primary focus of the model. In order to find the best way to classify EQs and QBs, the method looks at a number of ML models before settling on the best one using eight features. The results show that the suggested method, which uses the quadratic discrimination analysis model for discriminating, successfully separates EQs and QBs with a 99.4% success rate.

The investigation of geodynamics parameters in the south of Egypt using geodetic and earthquake activities

ABSTRACT Egypt’s southern region has significant economic and historical importance. However, due to the lack of data, this area has not gotten sufficient geodynamic research. Minor, to moderate earthquake activity along tectonic structures originating in the region from several faults is felt in southern Egypt. The study’s geographical scope includes the Red Sea coast, the Eastern Desert, the Western Desert, Aswan, and Nasser Lake, and it lies between 22° and 27° 30 N and 25° to 34° E. In this paper, the crustal deformation and earthquake events in the southern part of Egypt have been studied. The Global Navigation Satellite System (GNSS) observations taken by Egyptian Permanent Geodetic Network (EPGN) have been processed and adjusted for the period 2010–2019 using Bernese v.5.2 software. In addition, we investigate the source mechanism of the significant earthquakes ≥3 magnitudes using the waveform data recorded by the Egyptian National Seismic Network (ENSN) during the period 2012–2019. The focal mechanisms of these earthquakes were constructed with high reliability based on the P-wave first motion polarities. The results show that the average residual velocity concerning Nubian fixed is about 0.5 ± 0.25 mm in the east direction and 1 ± 0.3 mm in the north direction.

Development a local magnitude scale for South Egypt

A local magnitude (ML) scale for the southern Egypt region was developed using 3435 maximum amplitudes of 343 high-quality records of earthquakes recorded by the Egyptian National Seismic Network (ENSN). The analysis is started by the relocation of the recorded earthquakes, and then instrument responses were deconvolved from the recording and simulated on a standard Wood–Anderson torsion seismograph. Zero-to-peak amplitude of Sg or Lg waves in the two horizontal components is measured on each simulated Wood–Anderson seismograph. Events that were recorded by at least four stations and located at hypocentral distances between 10 and 1000 km and with a magnitude range of 1–4.5 are selected for preforming the analysis. The maximum recorded hypocentral depth was 40 km. The normalized amplitude decay shows two transition distances at 90 km, and 175 km yielding three segments. The trilinear regression model was adopted to retrieve three formulae that describe the local magnitude as follows:ML = log (A) + 1.4223*log(R) −0.0014*(R) +0.301 for R < 90.ML = log (A) +1.3786*log(R) −0.0014*(R) +0.379 for 90 < R < 175.ML = log (A) +3.1369*log(R) −0.0014*(R) −3.57 for R > 175.Where A is the ground displacement amplitude (mm) on the horizontal component, R is the hypocentral distance (km). The station corrections were also determined for 49 different geological sites using the regression model and producing values ranging between −0.4 and 0.7. The residual of magnitude values are reduced by 46% when using station corrections. The newly derived scale for South Egypt is well correlated with scales determined for South California and those for other intraplate areas, such as the Ethiopian Plateau and central US.

An Optimized Learning Model Augment Analyst Decisions for Seismic Source Discrimination

Efficient handling and planning for the urban regions’ sustainable development require a vast range of up-to-date and thematic information. Besides, obtaining an uncontaminated catalog of seismic activity is desirable to study the earthquake (EQ) clusters’ spatial allocation, which is a key role in mitigating seismic hazards and alleviating EQ losses by enhancing the assessment of seismic hazards. This article considers the northeastern part of Egypt where the seismicity catalog is contaminated by quarry blasts (QBs) operated throughout the mapped area. Consequently, it is desirable to discriminate these QBs from the EQs for genuine seismicity and hazard analysis. Accordingly, we provide an efficient machine learning (ML) model for decontaminating the seismicity database so that EQ clusters can be properly delineated by relying on 870 events (EQs and QBs) observed by only one seismic station called “GLL,” a member of the Egyptian National Seismic Network (ENSN). The model focuses on magnitudes < 3 that have high uncertainty of being EQs or QBs and take a long time for analysis. The approach examines several linear and nonlinear ML models and, finally, selects the best model with only two features leading to the optimal classification between the EQs and QBs. The optimization process is accomplished throughout two stages. The obtained results prove that the proposed scheme achieves 100% discrimination between the EQs and QBs relying on the extreme gradient boosting (XGB) model.

Relationship between precursory signals and corresponding earthquakes using different spectral analysis techniques

The origin of precursory signals that precede the P-waves is controversial, as it may be caused by ground effect (seismic nucleation phase) or instrumental effect due to a digitizer. Such signals cause errors in the automatic detection of P-wave arrival times and consequently decrease the accuracy of earthquake parameter estimations. In this paper, we proposed spectral analysis techniques to distinguish between different types of precursory segments, and to find if there is a relation between existence of these precursors and their corresponding earthquakes. These algorithms are applied to 1015 local events recorded by eleven permanent seismic stations belonging to the Egyptian National Seismic Network. Manual inspection of these events reveals the existence of these precursors. The investigations provided evidence that one type of these precursors originated because of an instrumental effect. This study shows the underlying causes of the precursory segment’s appearance prior to P-wave impulses. Many events had similar parameters; however, some of them had such precursors while others did not, in this inspection, multi resolution analysis details of the Discrete Wavelet Transform have been used. When large amplitudes for high frequency P-wave detail exceed 104 counts (1 count = 1 nm/s), the appearance percentage for the precursory segment is 100%.

Characteristics of Earthquakes Recorded Around the High Dam Lake with Comparison to Natural Earthquakes Using Waveform Inversion and Source Spectra

To determine whether recent seismicity around the High Dam Lake (Lake Nasser) in the Aswan region is induced or triggered by the lake reservoir or is of natural origin, we analyzed moment tensor solutions and source spectra of recent recorded earthquakes in the area. The earthquakes' focal mechanisms, including source mechanism parameters and source spectra, can give important information to assist in discriminating between triggered and natural seismic events. In the current work, we computed moment tensors and stress drop values for six recently triggered earthquakes recorded by the Egyptian National Seismic Network (ENSN) around Lake Nasser, Aswan area, with local magnitudes between 3.0 and 4.6, as well as 40 nearby earthquakes in and around Egypt with local magnitudes ranging from 4.0 to 5.5, that are known as natural events. We performed full waveform inversion for the studied seismic events, including the dominant double-couple (DC) signature, and also completed moment tensor solutions. Our results show that most triggered events demonstrated significant non-double-couple components. The focal depths of most Aswan seismic events calculated in the current study are significantly shallower than the estimated focal depths for inter-plate and intraplate earthquakes in and around the area under investigation. The focal depths of 80% of the triggered events are shallower than 10 km, while 80% of the tectonic earthquakes are deeper than 15 km. On the other hand, stress and source spectra of the studied events are used as another key to deeply study the source mechanics and physics of natural and triggered events in this area.

A homogenous moment magnitude and local magnitude scaling relation for earthquakes in Egypt

ABSTRACT In this work, we publish a moment-local magnitude scale catalogue for the Egyptian National Seismic Network (ENSN) since 1997 to 2019 as necessary for the study of seismicity and seismic hazard estimation. Every year, the ENSN publish an annual bulletin of local and regional earthquakes recorded by the network with local magnitude (Ml) scale. The ENSN was recorded more than 36,730 approximately for local events since 1997. In this work, the Moment magnitudes (Mw) are computed for small earthquakes using a spectral analysis method, while the Moment magnitudes of moderate and large earthquakes are obtained using a complete waveform inversion and moment tensor techniques. An empirical relationship between moment magnitude (Mw) and local magnitude (Ml) of the earthquakes are developed using a linear regression. The Mw–Ml relationship used in this study was as follows: Mw = 0.69 Ml + 0.58 for earthquakes with magnitude ≤3 Mw = 0.95 Ml – 0.15 for earthquakes with magnitude 3< ML≤6 The ENSN local magnitude (Ml) catalogue was converted to a moment magnitude (Mw) catalogue and attached as a supplementary material with this article for use by the researchers and authors in tectonic studies and seismic hazard evaluation of the region.

Real-time P-wave picking for earthquake early warning system using discrete wavelet transform

ABSTRACT P-wave picking is one of the important steps for earthquake parameter determination. Although manual inspection of P-wave arrival timing is the most accurate method for detection but, using automated algorithm is a must in order to facilitate this continuous task. In this research article an automated real-time algorithm is introduced to determine P-wave arrival timing of multiple of stations in a sub-network of the Egyptian National Seismic Network (ENSN). This algorithm generates a daily report of all events recorded by this sub-network. The main advantage of this proposed algorithm is its small processing time to give accurate P-wave arrival timings. This merit had been invested to make a proposal for Earthquake Early Warning (EEW) system using this algorithm. Additionally, this algorithm can detect very small events starting from micro-earthquakes due to the use of multiresolution analysis (MRA) of discrete wavelet transform (DWT). Results show a high rate of successful detections of 94.6%with low false alarm rate.

Seismic Activity and Energy Release of Earthquakes along the Gulf of Aqaba, Egypt

The Gulf of Aqaba is situated along the southern part of the Dead Sea Rift Area transform (DST), 1000 km (620 miles), the boundary between the African plate and the Arabian plate. It is situated toward the east of the Sinai landmass and west of Saudi Arabia. It is one of the joints interfacing the Asian and African landmasses. The Gulf expands 180 km from Eilat and Aqaba and joins the Red Sea in the Strait of Tiran, with the most extensive purpose of 28 km. On November 22, 1995, the biggest seismic tremor estimating 7.0 degrees happened along parts of the dead left line in the Gulf of Aqaba close to the port of Nuweiba in Egypt. This tremor made extraordinary harm Egypt and neighboring nations. Consequently, a few point by point investigations of seismology and geophysics have been led in the Gulf of Aqaba. In the territory researched, the vast majority of the ongoing seismic action revolved around the Gulf of Aqaba is portrayed by the contribution of moderate central quakes, an immediate aftereffect of the relative development between the plates of Africa, Sinai and the Arabian Peninsula. Seismic Energy along the Gulf of Aqaba locale is assessed utilizing a brief period (50 tests for every second) executed by the Egyptian National Seismic Network amid the period 1998‒2017. The connection between the dispatch and greatness of quakes in the Gulf of Aqaba demonstrated that the vast majority of the seismic Energy discharge originates from the biggest occasions and is packed in the inside, while it is moderately low in the southern and northern parts of the Gulf.

Source mechanisms and simulation of ground motions of 18 and 22 July 2014 Suez earthquakes

ABSTRACTOn 18th and 22nd of July, 2014, two felt earthquakes have occurred in the northeastern part of Egypt (Cairo-Suez District) near Suez city with magnitude ML = 4.3 and ML = 4.0 respectively. The datasets used involves the two earthquakes recorded by Egyptian National Seismic Network (ENSN) and regional seismic stations (Jordan and Cyprus) to obtain the focal mechanism. A stochastic method is used to obtain high-frequency ground motion synthetics based on local site effect using 5 sites ambient noise (Microtremor) measurements to obtain the resonance frequency of the sediments. The ground motion parameters of (PGA), (PGV), (PGD) and spectral accelerations (SA) of the two earthquakes are obtained. The results show that the maximum value of the peak ground acceleration is observed at the site no. 1 (Northwest the apex of the Suez Gulf) due to near source-site distance and local site conditions (H/V = 4.4), while the minimum value is observed at the site no. 5 (Southwest of the small Bitter Lake) due to a large distance from the source (H/V = 2.10). The damped pseudo-acceleration was applied for the simulation at damping (0.5%, 1%, 5%, 10% and 20%). These results indicated, the efficiency and the importance of the local site conditions on strong ground motions.

Present Kinematic Regime and Recent Seismicity of Gulf Suez, Egypt

In this study we computed recent seismicity and present kinematic regime in the northern and middle zones of Gulf of Suez as inferred from moment tensor settlings and focal mechanism of local earthquakes that happened in this region. On 18 and 22 of July, 2014 two moderate size earthquakes of local magnitudes 4.2 and 4.1 struck the northern zone of Gulf of Suez near Suez City. These events are instrumentally recorded by Egyptian National Seismic Network (ENSN). The earthquakes have been felt at Suez City and greater Cairo metropolitan zone while no losses were reported. The source mechanism and source parameters of the calculated events were considered by the near-source waveform data listed at very broadband stations of ENSN and supported by the P-wave polarity data of short period stations. The new settling method and software used deem the action of the source time function, which has been ignored in most of the program series of the moment tensor settling analysis with near source seismograms. The obtained results from settling technique indicate that the estimated seismic moments of both earthquakes are 0.6621E + 15 and 0.4447E + 15 Nm conforming to a moment magnitude Mw 3.8 and 3.7 respectively. The fault plan settlings obtained from both settling technique and polarity of first-arrival indicate the dominance of normal faulting. We also evaluated the stress field in north and middle zones of Gulf of Suez using a multiple inverse method. The prime strain axis shows that the deformation is taken up mainly as stretching in the E–W and NE–SW direction.

Earthquake source characterization, moment tensor solutions, and stress field of small-moderate earthquakes occurred in the northern Red Sea Triple Junction

We estimated moment tensor and centroid depth of eight small/moderate local earthquakes occurred between 2011 and 2013 in the northern Red Sea Triple Junction using a moment tensor inversion of near-source waveform data recorded by very broadband stations of the Egyptian National Seismic Network (ENSN). We also estimated the focal mechanism using the P-wave polarity data set and then compared it with the moment tensor inversion results. The moment tensor solutions are consistent with the focal mechanism obtained from the P-wave polarity data. We also estimated the stress field in the study area using the Multiple Inverse Method (MIM). Our results indicate that the axis of the minimum principal stress is a nearly horizontal NE-SW direction, while the axis of the maximum principal stress is nearly vertical. The direction of the minimum principal stress is consistent with the opening direction of the northern Red Sea zone, where the southern part of Gulf of Suez is currently under an extensional stress field with a NE-SW trending horizontal extension. These results are compatible with the kinematics of the Red Sea-Gulf of Suez rift.

SOURCE CHARACTERIZATION AND GROUND MOTION MODELING COMPUTED FROM THE 3 SEPTEMBER 2015 EARTHQUAKE, WESTERN DESERT, EGYPT

To obtain the characterized source model for prediction of strong ground motions, the ground motion generation area and rupture geometry of an inland crustal earthquake from near-source ground motion records has been estimated. An earthquake, with a magnitude of 4.3 ML and a focal depth of 18 km occurred on September 3, 2015 at 30.45N, 28.44E in the Western Desert of Egypt about 60 km south of El-Dabaa city. This earthquake is the first instrumentally recorded earthquake occurring in this area in several decades. The waveform data of this event has been used for source characterization and ground motion modeling. The present work describes the results of a preliminary study conducted to obtain fault plane solutions of this earthquake from waveform inversion and P-wave polarity. For this purpose, the source parameters related to the strong ground motion were estimated by waveform data and first arrivals recorded by the Egyptian National Seismic Network (ENSN) are used to arrive at focal mechanism solutions. Fault plane solutions for the main shock indicate strike-slip motion. One nodal plate strikes about 330°, is nearly vertical, and indicates right lateral slip. The other nodal plane strikes about 240°, dips very steeply NW, and indicates left lateral slip. Also the peak ground acceleration (PGA) at the El-Dabaa site has been simulated by taking into account an accurate estimation of the source characterization, the path attenuation model, and site amplification. The results have been validated using an actual recording of PGA at one ENSN station that recorded strong ground motion.

SEISMOTECTONIC HAZARDS ASSESSMENT IN SOUTHWESTERN SINAI AREA USING REMOTE SENSING AND GIS

Major national development projects have been accomplished in Egypt, particularly around the Gulf of Suez - Sinai region. These include construction of national industrial projects, roads, ports, power station, mineral exploration, beach and village's tourist construction. The aim of this study is to assess and map the seismic activity at the southwestern section of Sinai, Egypt. In the present work, remote sensing and Geographic Information System (GIS) techniques are applied using satellite images, topographical, geological and other ancillary geological data. GIS data integration and analysis indicated that the area is threatened to environmental seismotectonic hazard. These depend on the geological, local seismic activity and the structure analyses of data that are extracted from remote sensing and geo-references data. The structural lineaments analysis data extracted from enhanced Landsat 8 (OLI) image showed that major trends of seismic activity is strongly reduced along the segment fault system of the Gulf of Suez and Gulf of Aqaba. The main characteristics of the seismtectonics of the study area are investigated based on the geological data and seismic activity using the recently recorded data by the Egyptian National Seismic Network (ENSN), in the period between 1904-2005. Accordingly, the assessment of the seismic activity hazard was taken into consideration through identification of the sources of events. Almost all of these events (91.75%) were micro earthquakes and about 8.25% had small measurable magnitudes (4.4 > ML >=3.0). The statistical analyses and geospatial mapping are carried out to extracted structural lineaments and seismic activities. The integrated map of the seismotectonic is constructed and showing the distribution sites of the hazards anomalies. The distribution of seismic activity pattern and previously mentioned data analysis for the study area clearly showed the urgent need for an assessment and rehabilitation program to mitigate geo-hazard environmental in existing structures.

Automatic identification of fake patterns caused by short-width wavelets in seismic data

Despite the popularity of using the Haar wavelet filter in many applications, it sometimes introduces fake patterns into the multi resolution analysis (MRA) of seismic data. In this work, we compared different wavelet filters to demonstrate that these patterns are fake and not part of the original waveforms and to show that they are a result of using the Haar wavelet filter as a short-width wavelet. To achieve this, many seismic waveforms from two different sources: the Egyptian National Seismic Network (ENSN) and the High Sensitivity Seismograph Network Japan (Hi-net) are used with different wavelet filters. We propose an algorithm based on an autoregressive (AR) model to detect these patterns automatically and fully.

The crustal structure of Egypt and the northern Red Sea region

P-wave receiver functions from 26 stations in the Egyptian National Seismic Network (ENSN) have been modeled using the H-k stacking method and in a joint inversion method with Rayleigh wave group velocities to investigate crustal structure across Egypt and the northern Red Sea region. The new estimates of crustal structure, when combined with previous results, show that along the rifted margins of the Red Sea, Gulf of Suez and Gulf of Aqaba crustal thickness ranges from 25 to 30km, the average crustal Vp/Vs ratio is 1.77, and the average crustal shear-wave velocity is 3.6km/s. Beneath northern and central Egypt, including the Sinai Peninsula, crustal thickness ranges from 32 to 38km, the average crustal Vp/Vs ratio is 1.79, and the average crustal shear-wave velocity is 3.5km/s. Beneath southern Egypt, crustal thickness ranges from 35 to 40km, the average crustal Vp/Vs ratio is 1.76, and the average crustal shear-wave velocity is 3.7km/s. In southern Egypt, the crust is also characterized by a 10–20km thick mafic lower crust. These findings indicate that crust along the rifted margins of the northern Red Sea, and Gulfs of Suez and Aqaba have been thinned by about 5 to 10km. The thick mafic lower crust in southern Egypt can be attributed to suturing during the Neoproterozoic collision of east Gondwana against the Sahara metacraton. Overall, the structure of the crust in Egypt away from the northern Red Sea region is similar to the structure of Precambrian crust in many other parts of Africa.

Seismological aspects of the 27 June 2015 Gulf of Aqaba earthquake and its sequence of aftershocks

On 27 June 2015, a moderate earthquake with magnitude Mb 5.2 struck the Gulf of Aqaba near Nuweiba City. This event was instrumentally recorded by the Egyptian National Seismic Network (ENSN) and many other international seismological centres. The event was felt in all the cities on the Gulf of Aqaba, as well as Suez City, Hurghada City, the greater Cairo Metropolitan Area, Israel, Jordan and the north-western part of Saudi Arabia. No casualties were reported, however. Approximately 95 aftershocks with magnitudes ranging from 0.7 to 4.2 were recorded by the ENSN following the mainshock. In the present study, the source characteristics of both the mainshock and the aftershocks were estimated using the near-source waveform data recorded by the very broadband stations of the ENSN, and these were validated by the P-wave polarity data from short period stations. Our analysis reveals that an estimated seismic moment of 0.762 × 1017 Nm was released, corresponding to a magnitude of Mw 5.2, a focal depth of 14 km, a fault radius of 0.72 km and a rupture area of approximately 1.65 km2. Monitoring the sequence of aftershocks reveals that they form a cluster around the mainshock and migrated downwards in focal depth towards the west. We compared the results we obtained with the published results from the international seismological centres. Our results are more realistic and accurate, in particular with respect to the epicenteral location, magnitude and fault plane solution which are in accordance with the hypocentre distribution of the aftershocks.

Earthquakes focal mechanism and stress field pattern in the northeastern part of Egypt

Egypt is characterized by moderate size seismicity where earthquakes are distributed within several active regions. In the present study, we investigated the source mechanism of earthquakes using the digital waveform data recorded by the Egyptian National Seismic Network (ENSN) during the period from 2004 to 2008. The focal mechanisms are constructed with high reliability based on the polarity of the first motion of P-wave.These solutions are used to examine the mode of tectonic deformation and the present-day stress field pattern affecting on different tectonic provinces in the northern part of Egypt. The results demonstrate mainly a normal faulting mechanism with minor strike slip component generally trending parallel to the northern Red Sea, the Suez rift, Aqaba rift with their connection with the great rift system of the Red Sea and the Gulf of Suez and Cairo-Alexandria trend.The inversion technique scheme is used also in the present study for determining the regional stress field parameters for earthquake focal mechanism solutions based on the grid search method of Gephart and Forsyth (1984). The Results of the stress tensor using focal mechanisms of recent earthquakes show a prevailed tension stress field in N52°E, N41°E and N52°E for the northern Red Sea, Gulf of Suez and Gulf of Aqaba zone respectively.