Static Stress Drop Research Articles

Characteristics of Stress Drop and Energy Budget from Extended Slip-Weakening Model and Scaling Relationships

The extended slip-weakening model was investigated by using a compiled set of source-spectrum-related parameters, i.e. seismic moment Mo, S-wave velocity Vs, corner-frequency fc, and source-controlled high-cut frequency fmax, for 113 shallow crustal earthquakes (focal depth less than 25 km, MW 3.0~7.5) that occurred in Japan from 1987 to 2016. The investigation was focused on the characteristics of stress drop, radiation energy-to-seismic moment ratio, radiation efficiency, and fracture energy release rate, Gc. The scaling relationships of those source parameters were also investigated and compared with those in previous studies, which were based on generally used singular models with the dimensionless numbers corresponding to fc given by Brune and Madariaga. The results showed that the stress drop from the singular model with Madariaga’s dimensionless number was equivalent to the breakdown stress drop, as well as Brune’s effective stress, rather than to static stress drop as has been usually assumed. The scale dependence of stress drop showed a different tendency in accordance with the size category of the earthquakes, which may be divided into small-moderate earthquakes and moderate-large earthquakes by comparing to Mo = 1017~1018 Nm. The scale dependence was quite similar to that shown by Kanamori and Rivera. The scale dependence was not because of a poor dynamic range of recorded signals or missing data as asserted by Ide and Beroza, but rather it was because of the scale dependent Vr-induced local similarity of spectrum as shown in a previous study by the authors. The energy release rate Gc with respect to breakdown distance Dc from the extended slip-weakening model coincided with that given by Ellsworth and Beroza in a study on the rupture nucleation phase; and the empirical relationship given by Abercrombie and Rice can represent the results from the extended slip-weakening model, the results from laboratory stick-slip experiments by Ohnaka, and the results given by Ellsworth and Beroza simultaneously. Also the energy flux into the breakdown zone was well correlated with the breakdown stress drop,   and peak slip velocity of the fault faces. Consequently, the investigation results indicate the appropriateness of the extended slip-weakening model.

Stress drop–magnitude dependence of acoustic emissions during laboratory stick-slip

SUMMARYEarthquake source parameters such as seismic stress drop and corner frequency are observed to vary widely, leading to persistent discussion on potential scaling of stress drop and event size. Physical mechanisms that govern stress drop variations are difficult to evaluate in nature and are more readily studied in controlled laboratory experiments. We perform two stick-slip experiments on fractured (rough) and cut (smooth) Westerly granite samples to explore fault roughness effects on acoustic emission (AE) source parameters. We separate large stick-slip events that generally saturate the seismic recording system from populations of smaller AE events which are sensitive to fault stresses prior to slip. AE event populations show many similarities to natural seismicity and may be interpreted as laboratory equivalent of natural microseismic events. We then compare the temporal evolution of mechanical data such as measured stress release during slip to temporal changes in stress drops derived from AEs using the spectral ratio technique. We report on two primary observations: (1) In contrast to most case studies for natural earthquakes, we observe a strong increase in seismic stress drop with AE size. (2) The scaling of stress drop with magnitude is governed by fault roughness, whereby the rough fault shows a more rapid increase of the stress drop–magnitude relation with progressing large stick-slip events than the smooth fault. The overall range of AE sizes on the rough surface is influenced by both the average grain size and the width of the fault core. The magnitudes of the smallest AE events on smooth faults may also be governed by grain size. However, AEs significantly grow beyond peak roughness and the width of the fault core. Our laboratory tests highlight that source parameters vary substantially in the presence of fault zone heterogeneity (i.e. roughness and narrow grain size distribution), which may affect seismic energy partitioning and static stress drops of small and large AE events.

Source analysis of the March 7, 2019 mathbf {M_L=4.0} Somogyszob, Hungary earthquake sequence

Between February 16 and April 5, 2019, a series of earthquakes took place around the village of Somogyszob, Somogy county, Hungary. The mainshock occurred on March 7 with a local magnitude M_L=4.0 and epicentral intensity of 5 on the EMS scale. The main event was preceded by four foreshocks and followed by four aftershocks. The largest foreshock (M_L=2.6) was also felt with maximum intensity of 4 EMS. This earthquake sequence is the first remarkable one in the region that was recorded by a significant number of high-quality broadband digital seismographs. We have estimated the hypocenters of the 9 earthquakes using the hypoDD multiple-event location algorithm. The events occurred in a tight region around the mainshock at around 13–14 km depth. For the main event, we obtained an average moment magnitude of M_w=3.75, source radii of r^P=509 m and r^S=400 m, and static stress drops of varDelta sigma ^P=1.19times 10^6 Pa and varDelta sigma ^S=4.00times 10^6 Pa from the analysis of displacement P- and S-wave spectra, respectively. The resulting spectral source parameters for the investigated events agree well with the results of earlier research. We have also shown that our recently developed probabilistic waveform inversion techniques applied in this study are suitable to retrieve the source mechanism for weak local earthquakes. We have successfully estimated the focal mechanism for the mainshock, a foreshock and an aftershock. Each earthquake was a thrust faulting event with a sub-horizontal P-axis pointing towards N-NE, coinciding with the general trend of the compressional stress field in the epicentral region.

Detection Limits and Near‐Field Ground Motions of Fast and Slow Earthquakes

AbstractWe investigate theoretical limits to detection of fast and slow seismic events, and spatial variations of ground motion expected from M 6 earthquakes at short epicentral distances. The analyses are based on synthetic velocity seismograms calculated with the discrete wavenumber method assuming seismic velocities and attenuation properties of the crust in Southern California. The examined source properties include different magnitudes (M −1.0 to M 6.0), static stress drops (0.1–10 MPa), and slow and fast ruptures (0.1–0.9 of shear wave velocity). For the M 6 events we also consider variations in rise times producing crack‐ and pulse‐type events and different rupture directivities. Slow events produce ground motion with considerably lower amplitude than corresponding regular fast earthquakes with the same magnitude, and hence are significantly more difficult to detect. The static stress drop and slip rise time also affect the maximum radiated seismic motion, and hence event detectability. Apart from geometrical factors, the saturation and depletion of seismic ground motion at short epicentral distances stem from radiation pattern, earthquake size (magnitude, stress drop), and rupture directivity. The rupture velocity, rise time, and directivity affect significantly the spatial pattern of the ground motions. The results can help optimizing detection of slow and fast small earthquakes and understand the spatial distribution of ground motion generated by large events.

Rupture Process of the 7 January 2020, MW 6.4 Puerto Rico Earthquake

AbstractA vigorous shallow earthquake sequence along the southern coast of Puerto Rico commenced on 28 December 2019 in a region with little prior large seismicity. The largest event in the sequence (MW = 6.4), struck on 7 January 2020 and involved normal faulting. It produced extensive damage in southern Puerto Rico and power disruption across the island. Nearby strong ground motions and static offsets from GPS stations along with teleseismic recordings are inverted for the kinematic rupture process of the mainshock. The ~15‐km‐long rupture is spatially concentrated, with most slip between 3 and 13 km deep and peak slip of ~1.6 m. The static stress drop is high, ~19 MPa, with the rupture locating in the eastern section of a ~30‐km‐long band of seismicity bisected by a near‐orthogonal lineation. Complex faulting and high stress in the intraplate region appears to be responsible for the high earthquake productivity.

Parametric analysis of the elastohydrodynamic lubrication efficiency on induced seismicity

SUMMARY During reservoir stimulations, the injection of fluids with variable viscosities can trigger seismicity. Several fault lubrication mechanisms have been invoked to explain the dynamic stress drop occurring during those seismic events. Here, we perform a parametric analysis of the elastohydrodynamic fault lubrication mechanism to assess its efficiency during fluid-induced earthquakes. The efficiency of the mechanism is measured with the dimensionless Sommerfeld number S. Accordingly, we analysed eight well-documented cases of induced seismicity associated with the injection of fluids whose viscosities range from 1 mPa s (water) to 100 mPa s (proppant). We collected information related to the in situ stress field, fault orientation and geometry, moment of magnitude and static stress drop of the events. These parameters allow us to analyse the variation in the Sommerfeld number. Our results show that the estimated dynamic friction on the fault during the event is compatible with the fault weakening predicted by the elastohydrodynamic lubrication theory, particularly for highly viscous fluids.

Dynamic rupture simulations with heterogeneous initial stresses inversed from a given slip distribution: A case study of the 2017 Mw 6.5 Jiuzhaigou earthquake

Heterogeneous initial stresses are extremely important in understanding the physics of earthquake rupture processes. We propose a method to estimate heterogeneous initial stresses by comparing the slip from dynamic rupture simulations and the input joint inversion result and apply it to the 2017 Mw 6.5 Jiuzhaigou earthquake, which occurred in the intersection area of the Minjiang, Tazang and Huya faults, in Sichuan Province, China, with the slip distributed on two distinct left-lateral strike-slip faults as shown in previous geodetic and seismic joint inversion. We use the seismic efficiency empirical relation to infer the average stress, and the average stress drop is estimated using the static stress drop. With the angle of the maximum principal stress and the nucleation fault determined from the relocated aftershocks, different principal stresses are calculated with different combinations of average stress and average stress drop. The initial normal and residual stresses can be determined using the projection of the principal stresses. The initial shear stresses are generated by adding the residual stress and the heterogeneous stress drop, which is generated by a set of Gaussian random numbers with a given mean and the variance, and mapped one-by-one with the given slip on the fault so that the area with a large slip has a large stress drop. By comparing the slip from dynamic rupture simulations and the input joint inversion result, we show that the case with a 36 MPa average stress and 2.1 MPa average stress drop provides the best-fitting slip snapshots. The dynamic Coulomb stress change shows that the 2017 Mw 6.5 Jiuzhaigou earthquake could bring the southeast of the Tazang fault and the middle of the Minjiang fault closer to failure. This work provides a new insight to understand the initial stresses of nature earthquakes.

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.

Relationship Between Seismic Moment and Source Duration for Seismogenic Earthquakes in Taiwan: Implications for the Product of Static Stress Drop and the Cube of Rupture Velocity

A systematic analysis of the source duration (τ) and seismic moment (M0) for seismogenic earthquakes (MW 5.5–7.1) in the Taiwan region was completed by using a teleseismic P-wave inversion method. Irrespective of the source self-similarity, the M0–τ relationship derived in this study had a power-law form, namely M0 ∝ τ3, under the assumption that ΔσVr3 is constant following a circular fault model (Δσ: static stress drop; Vr: rupture velocity). For Taiwan’s earthquakes, the derived M0–τ relationship not only provides information to predict the source duration of large earthquakes, but also probes the rupture features of seismogenic earthquakes. That is, there are different rupture patterns for earthquakes, but the product ΔσVr3 remains nearly constant.

Moment–Area Scaling Relationship Assuming Constant Stress Drop for Crustal Earthquakes

ABSTRACTFor crustal earthquakes, the scaling relationship between the seismic moment M0 and rupture area S varies with the size of the earthquake, due to the limited thickness of the seismogenic layer. In those M0–S scaling relations, in most cases, the calculated static stress drop is altered with the size of earthquake, although the change depends on the assumed fault model. However, it is not clear whether the dependence of the stress drop on M0 is physically reasonable. In this study, the scaling relation between M0 and S, which assumes a constant stress drop over a wide M0 range, is discussed based on the analytical stress drop formula of a rectangular strike-slip fault. In the proposed relation, M0 is proportional to S3/2 for small and medium faults and to S1 for long faults. In addition, the relation between M0 and S varies in the intermediate range, depending on the aspect ratio. The scaling relation showed good agreement with past event data when the saturated rupture width was set to around 15–20 km and the stress drop was set to about 3 MPa.

Numerical Study on Earthquake Energy Partitioning: Relationships Among Radiated Energy, Seismic Moment, and Stress Drop

AbstractThis paper aims at mechanistically studying some aspects of earthquake energy partitioning with a focus on the radiated energy (Es) and seismic moment (Mo) relationships for investigating differences between estimates of average dynamic stress drop ( ) and static stress drop ( ). We evaluate to what extent a relatively simple but analytically verified faulting simulation can explain such differences. We adopt a numerical methodology developed in the 2‐D Universal Distinct Element Code to simulate fault slip with slip‐weakening responses. A method is introduced for recording the ground reaction to slip and from which we discuss the energy partitioning in ideal cases of rupture. We examine a shallow strike‐slip fault model where a locally peaked stress is gradually developed on the fault by applying tectonic stresses away from the fault surface until a rupture is initiated locally and propagated outward. The rupture is terminated when the available energy is exhausted by the fracture energy and friction work especially as the rupture is followed by a creep. With investigating roles of the available energy for rupture and the fracture energy, we display limited cases where Mo does not, at least proportionately, scale with Es. Results show this is because Mo, compared to Es, does not fully represent the energy available for initiating a rupture and the fracture energy consumed during its propagation. That is why 2μEs/Mo and 2μEs/ηRMo estimates, with the radiation ratio ηR and rigidity μ, may significantly differ from and .

The 4 January 2006 (Mw 6.6), San Pedro Martir Earthquake: Example of an Earthquake for Calibrating Excitation and Attenuation Studies

AbstractAn earthquake of magnitude 6.6 occurred on 4 January 2006, at 28.081° N and 112.381° W along a transform fault that joins the San Pedro Martir and the Guaymas basins in the Gulf of California extensional province. We located 17 foreshocks and 38 aftershocks. The foreshocks occurred on a fault perpendicular to the transform fault, where the main event occurred. The aftershocks were located along a fault length of approximately 18 km with a northwest–southeast trend. The average Brune static stress drop of the San Pedro Martir event was 8 MPa. From a time‐domain moment tensor inversion, we obtained the fault geometry given by strike of 129°±1°, dip of 86°±4°, and rake of 168°±12°, which was constrained to have a nonisotropic component and a source depth of 6±2 km. We used the inversion code from Yagi et al. (1999) to invert near field and teleseismic P waves to obtain the spatial slip distribution over the fault. The event had a single source and a moment rate function (MRF) displaying a triangular shape with a duration of 12 s. The rupture propagated toward the northwest from the hypocenter over a rupture area of 28×12 km2 with a maximum slip displacement of 2.3 m and a seismic moment of 8.79×1018 N·m. The directivity confirmed that the rupture propagated from the southeast to the northwest. Few aftershocks were located in the rupture area obtained from the inversion. Most aftershocks occurred toward the southeast of the epicenter. All these source analyses were performed to have a well‐calibrated excitation term for future regional modeling of ground‐motion parameters. The magnitudes of the foreshocks preceding this peculiar earthquake were higher than those of the aftershocks. Our results show that earthquakes with magnitudes of five or higher present a simple and self‐scaling law using a constant stress parameter, but for earthquakes with magnitudes lower than five, the high frequencies are depleted, and the earthquake can be replicated by a low‐stress parameter of 0.28 MPa. We also observed that the aftershocks and foreshocks differ in their frequency content. Although the foreshocks follow Brune’s omega‐squared source term, the aftershocks have larger contents of high frequencies.

Stable Forearc Stressed by a Weak Megathrust: Mechanical and Geodynamic Implications of Stress Changes Caused by the M = 9 Tohoku‐Oki Earthquake

AbstractRupture‐zone averaged static stress drop in the 2011 M=9 Tohoku‐Oki earthquake was less than 5 MPa, but it caused a stress reversal in most of the offshore forearc, although the reversal is less well constrained far offshore by earthquake mechanisms because of 20‐ to 30‐km errors in event depths. Using a finite element model of force balance, we demonstrate that the stress reversal unambiguously indicates (1) a very weak subduction megathrust and (2) very low differential stresses in the forearc. Prior to the reversal, the upper limit of megathrust strength could not be determined from forearc stresses. In the forearc, effects of megathrust friction and gravity are in a fragile balance, and stresses fluctuate around a neutral state in earthquake cycles. If most of the offshore forearc is to be compressive before but extensional after the earthquake, the effective friction coefficient of the megathrust must be ~0.032. Under low differential stresses associated with megathrust weakness, the forearc is generally well below yielding. Applying the concepts of dynamic Coulomb wedge, we show that the inner wedge, and by inference farther landward, stays stable throughout earthquake cycles. The outer wedge is stable most of the time but may occasionally enter a critical state during great earthquakes; its geometry suggests that complete stress drop of the underlying shallow megathrust is unlikely to have happened. We reason that the occurrence of earthquakes and active faulting under low stress in the stable forearc is due to heterogeneities in structure, stress, and/or pore fluid pressure.

Source parameter analysis of microearthquakes recorded around the underground gas storage in the Montello-Collalto Area (Southeastern Alps, Italy)

The study of seismic source parameters is crucial for understanding the origin of seismicity and retrieving information on the energy balance and the stress involved in earthquake rupture processes. In active tectonic areas, where underground industrial activities are carried out, such parameters may help to understand whether earthquakes are induced, triggered, or natural. The Montello-Collalto area (Southeastern Alps) is located in an active tectonic environment and hosts a depleted natural reservoir used to store gas. Since 2012, a high-quality seismic network monitors the microseismicity occurring around the underground gas storage reservoir to understand if the storage activity might induce seismicity. In this paper, we estimate the source parameters of low magnitude events representative of the seismicity occurring in the area surrounding the reservoir. The analysis includes a preliminary removal of the site effects, specifically computed within this study, from all the records. Then, using a parametric multistep inversion scheme, we estimate the seismic moment, the corner frequency and the static stress drop, that can be set as reference for the microseismicity occurring in the study area. All the investigated earthquakes show low seismic efficiency compatible with overshoot processes, which is typical of natural (i.e., tectonic) earthquakes. Our procedure can be implemented in other tectonic regions hosting underground industrial activities to support the decisional processes related to real-time monitoring.

Energy Budget of Intermediate‐Depth Earthquakes in Northern Chile: Comparison With Shallow Earthquakes and Implications of Rupture Velocity Models Used

AbstractWe calculate well‐resolved corner frequencies and radiated energies for a set of 96 earthquakes divided into two clusters located in the same tectonic setting but with different depths in northern Chile. Fifty‐three shallow events with a mean depth of 20 km are analyzed, along with 43 intermediate‐depth earthquakes with a mean depth of 110 km. We deduce and compare their static (stress drop Δσ) and dynamic (rupture energy EG and radiation efficiency ηR) source parameters and test the implications of different common assumptions on their depth dependence, such as stress drop invariance, strain drop invariance, or constant rupture velocities. Our data show that, in this zone of Chile, most of these models imply higher rupture velocities at depth than for shallow earthquakes. In these cases, high stress drop, high fracture energy release rate, and higher radiation efficiency are observed for intermediate‐depth earthquakes, suggesting short and impulsive ruptures.

Variation of seismic scalar moment–corner frequency relationship during development of a hydraulic fracture system

We propose to utilize the corner frequency and seismic scalar moment relation as a new approach to monitor temporal changes of static stress drop as well as rupture velocity during development of a hydraulic fracture system. We introduce a single parameter M1to describe a two-parameter relation (scalar moment and corner frequency relation) and analyze temporal variation of this two-parameter relation. Because M1relates rupture velocity and static stress drop, we can infer temporal variation of rupture velocity and stress drop quantitatively. The parameter M1is calculated in two case studies. We document that two types of fracturing processes exist: (1) stable rupture velocity and static stress drop during the development of rupture and (2) increase of rupture velocity and/or static stress drop while the fracture system develops. In the latter case, one possible scenario is increase of permeability at each fracture plane during development of the fracture system.

Energy-based average stress drop and its uncertainty during the 2015Mw 7.8 Nepal earthquake constrained by geodetic data and its implications to earthquake dynamics

The slip and static stress drop of the 2015 M-w 7.8 Gorkha, Nepal earthquake has been studied using its excellent near-source static observations and a newly developed finite fault inversion algorithm with an average stress drop constraint. A series of nonlinear inversions with different target stress drops are conducted to search for the solution that not only most accurately fits the geodetic data, but also has an energy-based stress drop, (Delta) over bar tau(E), matching the target value. Our result reveals that the misfit to the geodetic data gradually decreases when the (Delta) over bar tau(E) of the inverted slip model increases from 2 to 7MPa; but becomes nearly constant when (Delta) over bar tau(E) further increases. Hence, only the lower bound of (Delta) over bar tau(E), that is, (Delta) over bar tau(min)(E) (similar to 7 MPa), of the Gorkha earthquake can be constrained with near-fault geodetic measurements, consistent with our previous study using just far-field seismic data. The upper bound of (Delta) over bar tau(E) can be constrained with an extra constraint on the maximum local stress drop. An artificial upper bound can also be reached if using a large subfault size to represent the source. The lower bound of (Delta) over bar tau(E) leads to the lower bound of the apparent available energy and the upper bound of the radiation efficiency (eta(R), 0.09-0.15), though the latter is also sensitive to the determination of the radiated seismic energy. We find that the lower eta(R) and the reported high rupture velocity (80-93 per cent shear wave speed) can be reconciled by considering the aspect ratio of the dominant slip patch. We recommend using (Delta) over bar tau(min)(E) to replace various slip smoothing constraints to stabilize the finite fault inversion because of its clear physical meaning.

Longer Migration and Spontaneous Decay of Aseismic Slip Pulse Caused by Fault Roughness

AbstractIt has been known that natural faults possess rough profiles, which may play a vital role in earthquake dynamics. Here we examine the effect of fault roughness in the earthquake nucleation process using the rate and state friction law with the slip evolution law. The nucleation process on rough faults behaves as accelerating and migrating aseismic slip pulse, which is similar to previous studies for flat faults. However, the migration distance on rough faults is much larger than flat faults. The effect of fault roughness on the aseismic slip pulse migration is described by a single parameter known as the roughness drag, which depends on the amplitude, the minimum wavelength, and the Hurst exponent of the fault roughness profile. We also show that aseismic slip pulse cannot accelerate to dynamic rupture and ceases spontaneously if the roughness drag exceeds the static stress drop.

Anatomy of mining-induced fault slip and a triggered rockburst

Fault slips and triggered rockbursts pose a significant threat to the safety of mining personnel and infrastructure in deep coal mines. Sudden and dynamic slip may occur along a pre-existing fault characterized by the presence of contact between two opposite faces. Such slips are capable of changing the balance of forces when mining activity is conducted in the area surrounding the fault at depth and are accompanied by energy release that has the potential to cause serious damage to roadways and working faces. The aim of the comprehensive investigation reported here was to elucidate the evolution of the stress field surrounding a fault due to mining activity in adjacent working faces, using Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) numerical simulations, especially variations the high shear stress area. We then proposed the mining-induced fault slip mechanism. The evolution rule of sources during fault slip could be clearly explained using field microseism (MS) monitoring data, and the correlation between source parameters (e.g., static stress drop, peak particle velocity, and displacement) and fault slip was established. Correspondingly, the multi-parameter precursors of a rockburst induced by the fault slip were analyzed and summarized in detail. This work provides a number of reference points to be used for the warning and controlling of rockbursts triggered by fault slip in coal mines.

Determination of earthquake source parameters using the inversion of waveform data: A case of small earthquakes around High Dam Lake, Aswan region, Egypt

The earthquake source parameters of 310 seismic events recorded by Aswan broadband seismic network with local magnitude ranges from 0.9 to 3.5 are determined. The Generalized Inversion Technique (GIT) assuming that a reference site was applied to isolate the source one, site, and path effects from the observed displacement P-wave spectra by means of linear least square analysis. The inversion technique was formulated based on Brune's omega-squared source model. The long period asymptote and the corner frequency are two essential parameters to achieve the desired goals of the current study. The source parameters are estimated (seismic moment, static stress drop, dislocation area, corner frequency and source radius), using the displacement source spectra from P wave portion. The determined stress drop values range from 0.03 to 2.9 MPa, with an average of 0.3 MPa. The lower stress drop values obtained may reflect that reservoir–induced earthquakes have a lower stress drop. The stress drop doesn't show significant dependence on the earthquake depth in Aswan region. Seismic moment, source radius, and corner frequency range from, 1.50E+17 to 2.18E+20 dyne-cm, 31.7–194.3 m, and 6 to 34 HZ, respectively. The seismic wave attenuation through propagation, expressed by a quality factor indicated its frequency dependence with regression relation proportional to Qp=128f0.58 for P wave spectra. The low Q0 (quality factor at reference frequencyf0) value indicate that Aswan region is a seismically active region. The site responses obtained using the inversion technique show that the stations sites have peak amplitudes in high frequency from 10 to 40 Hz.