Obtained Source Parameters Research Articles

Source parameters and moment tensor inversion of April 11, 2020 (mb=4.4), the significant El-Negalah Earthquake, Matrouh, Egypt

ABSTRACT A moderate size felt earthquake with a body wave magnitude (mb = 4.4) shocked the western part of northern Egypt on 11 April 2020. The nature of this seismic source has yet to be fully understood. This paper presents an analysis of the seismic source of this significant earthquake. A robust hypocentral parameters estimation is performed by collecting the data from 29 seismic stations in the Eastern Mediterranean region to reduce the azimuthal gap within the available location. The full-waveform Moment Tensor Inversion (MTI) is applied to derive the faulting mechanism of the quake. The obtained solutions indicate a reverse faulting mechanism. The plausibility of the obtained mechanism is analysed in terms of measuring the Kegan angle and evaluating the stability of the resulting mechanism. The source parameters are estimated using the S-wave amplitude displacement spectra. The obtained source parameters indicate that the seismic moment (Mo) is 8.9 × 1015 Nm, the fault radius L is 1013 m, the stress drop (σ) is 3.8 MPa, and the displacement (d) is 0.053 m. The analysis of this seismic source is of fundamental importance for evaluating seismic hazard in northern Egypt, particularly for critical facilities and safe hydrocarbon exploration.

Source parameters and scaling relations for small earthquakes in mainland Gujarat region of Western Deccan Volcanic Province, India

The return period of large earthquakes in intraplate regions is more in comparison to the interplate regions. Also, the intraplate region is less instrumented and hence, these regions are devoid of acceleration time histories of large and great earthquakes. The mainland Gujarat region is one of such intraplate regions for which acceleration time histories are not available, however, is vulnerable for earthquakes of M ∼ 6.0. Simulation is performed in these scenarios and the prerequisite is the knowledge of source parameters and scaling laws. We analyzed the spectra of the P- and S-waves recorded by the stations of Gujarat Seismic Network for the mainland Gujarat region of western Deccan Volcanic Province, India. Additionally, we developed scaling laws based on the obtained source parameters. We analyze 177 digital records from 43 local earthquakes during the period 2007–2016 with a magnitude of Ml = 2.5–4.3, which are located in a distance range of 10–250 km, using Brune’s seismic source model (Brune 1970, 1971). According to our study, the calculated stress drop values do not vary considerably with seismic moment values and are generally between 1 and 100 bar for most of the events. Therefore, the earthquakes in this region adhere to the law of self-similarity. As widely observed for conventional earthquakes, we find an inverse relationship between seismic moment and corner frequency for these events. Based on a linear regression analysis between the assessed seismic moment (M 0) and corner frequency (fc), we developed the scaling relation M 0 f c 3 = 2.29 × 1015. Scaling relations developed here are in agreement with those developed for the nearby Kachchh region and various other seismically active areas around the world. Use of regional scaling is recommended instead of global scaling laws for better estimation of seismic hazard. The source parameters and scaling laws presented here can be used for a variety of applications in mainland Gujarat, including the assessment of seismic hazards and the development of earthquake scenarios.

Rupture process assessment of rock bursts in a coal mine: Inversion of source parameters and the slip distribution on the rupture surface

To assessment the source parameters and slip distribution on the rupture surface of a rock burst event in Qianqiu coal mine, and verify the accuracy of the source parameters and slip distribution on the rupture surface, four rock burst events in Qianqiu coal mine were selected for source analysis. Firstly, the source parameters of four rock burst events in Qianqiu coal mine were obtained based on the Brune model. Then, the rupture scale and average slip on the rupture surface of seismic source were identified by using the established relationship between rupture scale and moment magnitude. Finally, based on the k2 rupture-slip model and the obtained source parameters, the slip distribution on the rupture surface was inverted to reveal the slip-rupture process of the source, and the accuracy of the seismic source parameters and the slip distribution on the rupture surface was verified based on the in-situ rupture-slip behavior. The results show that: the source parameters can be calculated using the Brune model and grid search method; the rupture scale and average slip on the rupture surface were obtained by establishing the relationship between the moment magnitude and the rupture scale of the source; based on the k2 rupture-slip model and the scale of rupture, the slip distribution on the rupture surface of a microseismic event in a coal mine can be deduced by inversion. The calculated source parameters and slip distribution of four rock burst events are consistent with the actual records of such events in a coal mine, which further verifies the accuracy of the source parameters and slip distribution of rock burst events. These results can be used to quantify and evaluate the rupture properties, scale and process of a rock burst, and provide reference for further study of the evolution process and risk assessment of rock burst events in coal mine.

Seismic source characterization of the Arabian Peninsula and Zagros Mountains from regional moment tensor and coda envelopes

Reliable estimates of moment magnitude and source mechanism for seismic events in the Middle East can be challenging due to a small number of openly available stations, the complex tectonic setting, and regions of high attenuation. Access to high-quality waveform data from well-calibrated regional seismic stations is fundamental in producing robust and stable estimates of earthquake source parameters, particularly when measurements of absolute ground motion amplitudes are required. Earthquake source mechanism and moment magnitude are invaluable information in the assessment of seismic hazard, plate motions, and the characterization of faults and regional stress field. The expansion of the Kingdom of Saudi Arabia’s national seismic network in the past several decades provides an opportunity to develop the capabilities of routine focal mechanism and moment magnitude estimations. In this study, we use time-domain full waveform moment tensor inversion and coda envelope–derived amplitude measurements to solve for earthquake source mechanism, moment magnitudes, and their source type. We compared the moment magnitudes calculated from the two methods and publicly available earthquake catalogs and discuss the implications of the obtained source parameters.

Source characterizations of the New Cairo earthquake, Egypt

The New Cairo region was hit by a moderate size earthquake (Mw = 4.18) on midday Monday, 31st December 2018 that was felt throughout the greater Cairo region without any reported damage. The source mechanism solution and moment tensor inversion exhibit a normal fault with a minor strike-slip component. The NW-fault plane is the preferred rupture plane consistent with the geological and tectonic settings of the region. The dynamic source parameters have calculated, assuming a simplified circular source model, by using displacement spectra. The obtained source parameters are included average seismic moment is 2.41E+15 N-m, rupture radius of 0.46 Km, stress drop is 10.9 MPa, relative displacement is 0.012 cm, and energy releases are 1.2E+18 Erg. According to “Scholz” (1990), the studied earthquake might be considered as an intraplate type-(II) earthquake that related to plate boundaries. In the present study, the thermal infrared data is used to derive Land Surface Temperature (LST) as a precursory analysis for this earthquake. The results indicated that there was a correlation between LST with precursor seismic activity before the time of the New Cairo earthquake occurrence.

Source parameters for small-moderate earthquakes in Marmara Region (Turkey)

The main aim of this study is to investigate the self-relation and self-similarity of earthquakes in and around the Marmara Sea (NW Turkey) by using these obtained source parameters. With this purpose, spectral source parameters for 77 small to moderate earthquake (3.5 ≤ ML ≤ 5.2) that occurred during 2004–2018 have been determined from P and S wave spectra according to Brune’s source model by using regional broadband seismograms. The average ratio of P/S wave corner frequency is found to be 1.3 that suggesting higher corner frequency for P wave. The static stress drops range from 0.1 and 136 MPa with a median value of 9.8 MPa (98 bars). The high stress drops for these events can indicate high frictional strength and low strain-rate of the faults. Similarly, the low values of the stress drop can indicate a general weakness of the faults in the study area. There is no clear dependence between the seismic moment and the static stress drop in the analyzed events but some events which have lower seismic moment value also have lower stress drop. Obtaining results indicated the corner frequency decreases with increasing of the seismic moment. Also, a slight depth dependence of the corner frequency has been observed for the analyzed events. Shallower events have larger corner frequency value than deeper events. Also, a clear depth dependence of the stress drop values has not been observed. However, the depth dependence of the seismic moment is seen more clearly. Our results indicated that the deeper events have larger seismic moment values in the study area. In spite of scattering in small events, a linear relationship between local magnitude (ML) and moment magnitude (MW) could be obtained as MW = 1.4261(± 0.31) + 0.6399(± 0.08)ML from P waves spectra and MW = 0.0136(± 0.21) + 0.9883(± 0.05)ML from S wave spectra and calculated MW values are consistent with waveform inversion (centroid moment tensor — CMT) results. These relationships may be useful for seismic hazard studies in the study area.

Evaluation of deep moonquake source parameters: Implication for fault characteristics and thermal state

AbstractWhile deep moonquakes are seismic events commonly observed on the Moon, their source mechanism is still unexplained. The two main issues are poorly constrained source parameters and incompatibilities between the thermal profiles suggested by many studies and the apparent need for brittle properties at these depths. In this study, we reinvestigated the deep moonquake data to reestimate its source parameters and uncover the characteristics of deep moonquake faults that differ from those on Earth. We first improve the estimation of source parameters through spectral analysis using “new” broadband seismic records made by combining those of the Apollo long‐ and short‐period seismometers. We use the broader frequency band of the combined spectra to estimate corner frequencies and DC values of spectra, which are important parameters to constrain the source parameters. We further use the spectral features to estimate seismic moments and stress drops for more than 100 deep moonquake events from three different source regions. This study revealed that deep moonquake faults are extremely smooth compared to terrestrial faults. Second, we reevaluate the brittle‐ductile transition temperature that is consistent with the obtained source parameters. We show that the source parameters imply that the tidal stress is the main source of the stress glut causing deep moonquakes and the large strain rate from tides makes the brittle‐ductile transition temperature higher. Higher transition temperatures open a new possibility to construct a thermal model that is consistent with deep moonquake occurrence and pressure condition and thereby improve our understandings of the deep moonquake source mechanism.

Inversion of Source Parameters from Magnetic Anomalies for Mineral/Ore Deposits Exploration Using Global Optimization Technique and Analysis of Uncertainty

Global optimization algorithm using very fast simulated annealing has been used for modeling of magnetic anomaly over various idealized geobodies for mineral/ore deposit investigation. The present technique shows that it can match the observed data very well assuming some simple geometrical bodies such as sphere, horizontal cylinder and thin dyke or sheet. Uncertainty associated with the modeling was also studied. It has been found that the obtained source parameters are strongly identical when all the parameters are optimized. The present study shows that amplitude coefficient depends on the shape factor. The relation between them shows a multimodel-type uncertainty. The shape factor modeled from several VFSA runs shows the different kind of subsurface structure. Constraining the shape factor gives reliable results and analysis of histograms and cross-plots also gives the utmost reliable results, which show a unimodel character. Inversion of synthetic noise-free and noisy data shows the worth of the present work. The present algorithm was also tested in five field case studies for mineral/ore exploration. Computation time for this present work is very minimal.

Source parameters of the 2005–2008 Balâ–Sırapınar (central Turkey) earthquakes: Implications for the internal deformation of the Anatolian plate

Active tectonics of central Anatolia is mainly governed by the collision of the African, Arabian and Anatolian plates, which causes westward escape of Anatolia along the North and East Anatolian Fault zones, and the counterclockwise rotation of the Kırşehir block with insignificant internal deformation. The formation of the present-day tectonic processes in this region can be deduced from geophysical prospecting and seismological data. Although the seismicity in central Anatolia is distinctively lower than that in the northern and eastern parts of the Anatolian plate, small and moderate earthquakes (2.5≤Mw≤6.0) mostly occurred in the region in the past decades or so. For example, intense earthquake activity was observed in the Balâ–Afşar–Sırapınar (Ankara, central Anatolia) region in the period of 2005 to 2008 with destructive earthquakes of July 30, 2005 (Mw=5.2); December 20, 2007 (Mw=5.7) and December 26, 2007 (Mw=5.6). Therefore, these earthquakes are crucial to analyze the shallow crustal deformation in the central Anatolian block. In the present study, we obtained source parameters of 2005–2008 earthquake sequence using the regional moment tensor (RMT) inversion method. We analyzed complete broad-band waveforms recorded at near-field distances (0.45°≤Δ≤3.6°). Our results reveal NW–SE directed right-lateral strike-slip faulting and NE–SW directed left-lateral strike-slip faulting mechanisms, which are clearly correlated with the conjugate fault systems in the Balâ–Afşar–Sırapınar region. However, some earthquakes also have E–W directed normal faulting components. We suggest that the major characteristics of 2005–2006 and 2007–2008 earthquake activity could have been dominantly associated with left-lateral and right-lateral strike-slip faulting mechanisms, respectively. The seismogenic depth is found to be about 8–10km. This result implies that earthquakes in the study region occurred mostly in the upper crust, which accommodates the strain by brittle deformation. Furthermore, our results are consistent with neotectonic features and available geophysical data (e.g., gravity, aeromagnetic and paleomagnetic) reported by previous studies. It may be envisioned that the joint interpretation of earthquake source parameters with those observations will shed light into the complex deformation processes for future studies.

Source parameters and moment tensor of the ML 4.6 earthquake of November 19, 2011, southwest Sharm El-Sheikh, Egypt

The southern part of the Gulf of Suez is one of the most seismically active areas in Egypt. On Saturday November 19, 2011 at 07:12:15 (GMT) an earthquake of ML 4.6 occurred in southwest Sharm El-Sheikh, Egypt. The quake has been felt at Sharm El-Sheikh city while no casualties were reported. The instrumental epicenter is located at 27.69°N and 34.06°E. Seismic moment is 1.47 E+22dynecm, corresponding to a moment magnitude Mw 4.1. Following a Brune model, the source radius is 101.36m with an average dislocation of 0.015cm and a 0.06MPa stress drop. The source mechanism from a fault plane solution shows a normal fault, the actual fault plane is strike 358, dip 34 and rake -60, the computer code ISOLA is used.Twenty seven small and micro earthquakes (1.5⩽ML⩽4.2) were also recorded by the Egyptian National Seismological Network (ENSN) from the same region. We estimate the source parameters for these earthquakes using displacement spectra. The obtained source parameters include seismic moments of 2.77E+16–1.47E+22dynecm, stress drops of 0.0005–0.0617MPa and relative displacement of 0.0001–0.0152cm.

Source parameters of the 2007 earthquake sequence, Aswan, Egypt

An earthquake sequence occurred in Aswan area during the period from April 2007 to December 2008. The spectral analysis technique was performed for some earthquakes ( M D 2.0–3.3) to obtain the earthquakes source parameters, such as: seismic moment ( M o ), corner frequency ( f o ), fault radius ( r o ), stress drop (Δ σ), average displacement across the fault ( d o ), and the moment magnitude ( M w ). The earthquakes source parameters were determined using PITSA and Matlab7 software programs. The derived corner frequencies f o for P-wave spectra show values range between 7.27 and 9.02 Hz, the seismic moments M o are varied from 0.16 × 10 20 to 2.7 × 10 21 dyne/cm, the source radii r are spanned between 2.78 and 342 m, while the stress drops Δ σ are varied from 0.34 to 29.3 bar. Some scaling relations between the different obtained source parameters were derived such as: M o – M D , M o –Δ δ, and the moment magnitude M w – M D . This is to deduce the empirical relations for these parameters, which can help in turn in the fast calculation of the different source parameters for the inherited earthquakes of the area.

Determination of the earthquake source parameters at Tushka area and its surroundings, Aswan, South Egypt

In the last few years, Tushka area received a special attention from the Egyptian government to construct new projects, cities and cultivation of more new areas. No historical earthquakes are known in the Tushka area. The spectral analysis was performed to obtain the source parameters of some earthquakes with magnitude M D ranging between 2.0 and 3.7 located in and around the area. The source parameters were determined using the MAG software program. The derived corner frequency ƒ o for P- and S-waves show values between 3.9–10.7 and 3.7–12.5 Hz respectively, the seismic moment M o ranged from 7.77 × 10 11 to 1.77 × 10 14 dyne/cm, the source radii r spanned from 49.2 to 136.5 m, the stress drop Δ δ varied from 1.17 to 778.3 bar and the seismic energy E ranged from 6.42 × 10 5 to 1.24 × 10 11 J. Some scaling relations between the different obtained source parameters were made such as: M o – M D M o –Δ δ, M o – E, and moment magnitude M w – M D in order to deduce the empirical relations for these parameters that can help in turn in the fast calculation of the different source parameters for the earthquakes in the area.

Source parameters of the ML 4.1 earthquake of November 08, 2006, southeast Beni-Suef, northern Egypt

In the early morning hours on Wednesday November 08, 2006 at 04:32:10(GMT) a small earthquake of M L 4.1 has occurred at southeast Beni-Suef, approximately 160 km SEE of Cairo, northern Egypt. The quake has been felt as far as Cairo and its surroundings while no casualties were reported. The instrumental epicentre is located at 28.57°N and 31.55°E. Seismic moment is 1.76 E14 Nm, corresponding to a moment magnitude M w 3.5. Following a Brune model, the source radius is 0.3 km with an average dislocation of 1.8 cm and a 2.4 MPa stress drop. The source mechanism from a first motion fault plane solution shows a left-lateral strike-slip mechanism with a minor dip-slip component along fault NNW striking at 161°, dipping 52° to the west and rake −5°. Trend and plunging of the maximum and minimum principle axes P/T are 125°, 28°, 21°, and 23°, respectively. A comparison with the mechanism of the October, 1999 event shows similarities in faulting type and orientation of nodal planes. Eight small earthquakes (3.0 ⩽ M L < 5.0) were also recorded by the Egyptian National Seismological Network (ENSN) from the same region. We estimate the source parameters and fault mechanism solutions (FMS) for these earthquakes using displacement spectra and P-wave polarities, respectively. The obtained source parameters including seismic moments of 4.9 × 10 12–5.04 × 10 15 Nm, stress drops of 0.2–4.9 MPa and relative displacement of 0.1–9.1 cm. The azimuths of T-axes determined from FMS are oriented in NNE–SSW direction. This direction is consistent with the present-day stress field in Egypt and the last phase of stress field changes in the Late Pleistocene, as well as with recent GPS measurements.

A SOURCE PARAMETERS STUDY OF THE AFTERSHOCK SEQUENCE OF THE KOZANI- GREVENA 1995 EARTHQUAKE BASED ON ACCELERATION RECORDS

Strong motion recordings of the May 13, 1995 Mw=6.6, earthquake sequence that occurred in the Kozani-Grevena region (Western Macedonia, Greece) have been analyzed for the determination of their source parameters. The data set for this study comes from a temporarily deployed accelerograph network and the source parameters using the shear-wave displacement spectra have been estimated. For this estimation the spectral records have been corrected for the site effects and for the propagation path (geometrical spreading and anelastic attenuation). The magnitude of each event was also re-calculated by estimating appropriate station corrections. The derived relationships arelogMo =(1.43 ±0.09) M, + (16.92 ± 0.29), 2.0 &lt; ML&lt; 5.0 (1)logfc = (-0.56± 0.08) · ML + (2.52 + 0.29), 2.0 &lt; ML&lt; 5.0 (2)logM0 = (-2.20 + 0.08) · log fc + (23.16 ± 0.84), 0.6 &lt; fc &lt; 10.0 (3)The near-surface attenuation parameter κ0 has also been determined for the strong motion stations sites. These values of κ0 are in good agreement with those of Margaris and Boore (1998) for the geological formation on which each station was positioned. The obtained source parameters are in good agreement with those from previous studies for the Aegean region.

S-wave spectral analysis of the 1995 Kozani-Grevena (NW Greece) aftershock sequence

S-wave spectral analysis is applied to 174 strong motion accelerationrecords to obtain the source parameters of 27 aftershocks(3.1 ≤ ML ≤ 4.3) of the May 13, 1995, Mw 6.6,Kozani-Grevena (NW Greece) earthquake. The data are derived from atemporary network, of three-component digital accelerographs, deployedwithin the strongly affected area some days after the mainshock occurrence.Site effects were evident in the strong motion records at 3 out of the 4stations used, and a correction was applied to account for theoverestimation of seismic moment due to amplification of thelow-frequency part of the spectrum. The data from this analysis arecomplimented with previously obtained source parameters for earthquakesin Greece, in order to study the applicability of the empirical scalingrelations used so far, towards smaller magnitudes. In general, a goodcorrelation was observed in most cases, validating the use of empiricalrelations that are applicable to the Aegean area. Empirical relations aredetermined between seismic moment and seismic slip, as well as, betweenseismic moment and stress drop, applicable to small magnitude earthquakes(ML < 4.3). Stress drop values were found to be relatively small,ranging from 2 to 41 bars, indicative of inter-plate environments. Thevalues of fc and of fmax were found in good agreement withrelations based on observations from larger worldwide earthquakes.

Moment tensor inversion for near earthquakes using long-period digital seismograms.

The possibility of rapid determination of source parameters (seismic moment and fault parameters) for near earthquakes is examined by means of the moment tensor inversion method. Numerical experiments of linear moment tensor inversion are made for a hypothetical source-station geometry appropriate for the Japanese region and suggest that it may be possible to determine the source parameters for the near earthquakes within about 10 min after the earthquake occurrence, provided that high-quality long-period seismic waveform data can be used. Source parameters of eight earthquakes (MW > 6.0) which occurred near the Japanese region during the period from November 1986 to April 1987 are determined by applying the inversion method to three-component long-period digital data recorded at a single station in Japan. The obtained source parameters are in good agreement with the solutions derived from global networks. The centroid-moment tensor (CMT) inversion method, solution of which is a result of simultaneous inversion of waveform data for the hypocentral parameters (epicentral coordinates, depth, origin time, and moment tensor) of the best point source, is applied to both synthesized and observed data. The inversion of synthesized data suggests that the CMT inversion to determine the hypocentral and source parameters simultaneously for near earthquakes may be possible in the Japanese region. We applied this method to the eight events, but we could obtain the CMT solution for only one event. The short propagation time and inadequate station coverage in the case of the single-station observation of the near earthquakes might have caused the non-uniqueness and instability in the determination of the CMT solutions. The numerical experiments suggest that this problem may be significantly remedied by the improvement of the station coverage.