Master Event Research Articles

Analysis of the southeast Beni-Suef, northern Egypt earthquake sequence

On 11 October 1999, a moderate earthquake of local magnitude ML 4.9 hit northern Egypt. This event shook the greater Cairo region and northern part of the Nile valley and was felt in much of northern Egypt with epicentral intensity of V (EMS). It was followed by eight aftershocks with local magnitude ranging from 1.6 to 3.2. A detailed analysis of this sequence, cross-correlation analysis, fault plane solutions and source parameter estimations is performed in the present article. A cross-correlation analysis allowed us to recognize a number of correlated events, which were used for earthquake ancestry using a master event technique. The focal mechanism solutions for the main-shock and the largest aftershock are moderately controlled and indicate strike-slip faulting with a dip-slip normal component. Rupture directivity, aftershock distributions and isoseismal lines were combined in an attempt to determine which of the two nodal planes is the fault plane. The dynamic source parameters of the southeast Beni-Suef earthquake sequence have been estimated from the P-wave spectra of the Egyptian National Seismograph Network (ENSN). The spectral amplitude of the main shock records displayed two distinct corner frequencies that reflect a complex rupture process. The averaging of the obtained values at different stations shows that the main shock occurred on a fault length of 1.5 km with relative displacement 9 cm, stress drop of 49 bar and seismic moment of 5×1022 dyn/cm. The aftershocks show a relatively similar source parameters fault length of 0.3⩽L⩽0.6 km, relative displacement of 0.05⩽u⩽0.2 cm, seismic moment of 2.3×1019⩽M0⩽1.1×1020 dyn.cm and stress drop of 0.7⩽Δσ⩽4 bar.

The October 15, 1997 Punitaqui earthquake (Mw=7.1): a destructive event within the subducting Nazca plate in central Chile

The 1943 Illapel seismic gap, central Chile (30–32°S), was partially reactivated in 1997–1998 by two distinct seismic clusters. On July 1997, a swarm of offshore earthquakes occurred on the northern part of the gap, along the coupled zone between Nazca and South American plates. Most of the focal mechanisms computed for these earthquakes show thrust faulting solutions. The July 1997 swarm was followed on October 15, 1997 by the Punitaqui main event (Mw=7.1), which destroyed the majority of adobe constructions in Punitaqui village and its environs. The main event focal mechanism indicates normal faulting with the more vertical plane considered as the active fault. This event is located inland at 68-km depth and it is assumed to be within the oceanic subducted plate, as are most of the more destructive Chilean seismic events. Aftershocks occurred mainly to the north of the Punitaqui mainshock location, in the central-eastern part of the Illapel seismic gap, but at shallower depths, with the two largest showing thrust focal mechanisms. The seismicity since 1964 has been relocated with a master event technique and a Joint Hypocenter Determination (JHD) algorithm, using teleseismic and regional data, along with aftershock data recorded by a temporary local seismic network and strong motion stations. These data show that the 1997 seismic clusters occurred at zones within the Illapel gap where low seismicity was observed during the considered time period. The analysis of P and T axis directions along the subduction zone, using the Harvard Centroid Moment Tensor solutions since 1977, shows that the oceanic slab is in a downdip extensional regime. In contrast, the Punitaqui mainshock is related to compression resulting from the flexure of the oceanic plate, which becomes subhorizontal at depths of about 100 km. Analog strong motion data of the Punitaqui main event show that the greatest accelerations are on the horizontal components. The highest amplitude spectra of the acceleration is in the frequency band 2.5–10 Hz, in agreement with the energy band responsible for the collapsed adobe constructions. The isoseismal map derived from the distribution of observed damage show that a high percentage of destruction is due to the proximity of the mainshock, the poor quality of adobe houses and probably local site amplification effects.

The relative locations of multiplets in the vicinity of the Western Almería (southern Spain) earthquake series of 1993-1994

SUMMARY We have analysed 721 earthquakes (1.5jmbj5.0) of the 1993–1994 Western Almero ´a (southern Spain) series and the following seismicity in the area until 1998. Among the data there are several multiplets, events characterized by very similar seismograms at the short-period stations of the local network. We detected similar seismograms using crosscorrelation analysis of the P and S arrivals and classified similar events into families, or clusters. We found 39 multiplet clusters of 3–33 events. Within each cluster, relocations relative to a master event have been calculated by using the interpolated cross-correlation maxima for the precise relative timing of P and S phases at each station. Relative arrival times have been compared for all the possible selections of the master event, and adjusted by forming the mean value after removing the outliers. The distribution of the stations does not permit a satisfactory resolution of focal depths, but relative epicentres have been determined with an accuracy of a few tens of metres. Typically they draw well-defined lineaments and show two dominant strike directions: N120u–130uE and N60u–70uE. These directions are coincident with known fault systems in the area and with the source parameters of three of the largest events (Mw=4.8, 3.6 and 4.9), which were estimated from waveform modelling of near-field acceleration records at a single station. Consistent with previous studies, distances within multiplets (typically several tens of metres) are for the most part clearly smaller than the fracture radii of these events. This indicates repeated slip on the same fault segment. It was possible to obtain precise relative locations between several nearby clusters, thereby imaging a very heterogeneous seismotectonic fine structure of the source area, i.e. the positions of adjacent active fault segments and the fragmentation of the crust into small (approximately 1 km) tectonic blocks.

Research On Source Characteristics And Seismogenesis Of The Jiashi Earthquake Swarm, Western China

AbstractThe 1997 Jiashi swarm earthquakes are relocated by using the “master event” method. From the precise relative locations and focal mechanisms of MS ≥ 5.0 earthquakes we infer that a pair of right‐step echelon fault segments, striking NNW‐SSE and slipping right laterally, may exist in the source region. 2177 polarity readings of P‐wave first motions are inverted for the average focal mechanism of the swarm earthquakes. Based on the Silver's source model[1], the main fracture characteristics of the earthquake faults are inferred from the observed source spectra. We have calculated the perturbed stress field generated by the motion of echelon fault segments and explained some source characteristics of the swarm earthquakes. An echelon fault model is introduced to the diversity of focal mechanisms and low stress drop of the Jiashi earthquakes. The paper suggests that the echelon fault structure in the source region is responsible for the multiplicity of strong earthquake occurrence.

Evidence for earthquake interaction in central Chile: the July 1997–September 1998 Sequence

Seven Mw > 6 events occurred between July 1997 and January 1998 along the shallow dipping subduction zone of Central Chile. We used body waveform modeling and master event relocation to study them. During July 1997, typical shallow interplate thrust events located close from each other followed a southward migration path and were located close from each other. On 15 October, the largest shock of the series (Mw=7.1) occured at 68 km depth. From the directivity, we found that its rupture plane was almost vertical with a downward rupture. It was a down‐dip compressional mechanism which is rare in Chile. Then, several thrust events occurred above it, along the plate interface. The rupture zones of the July 1997 events followed a cascade pattern with strong stress interaction. The slab push event of 15 October does not seem to have been triggered by static stress transfer from the July swarm.

Calibration of the Regional Crustal Waveguide and the Retrieval of Source Parameters Using Waveform Modeling

Regional crustal waveguide calibration is essential to the retrieval of source parameters and the location of smaller (M < 4.8) seismic events. This path calibration of regional seismic phases is strongly dependent on the accuracy of hypocentral locations of calibration (or master) events. This information can be difficult to obtain, especially for smaller events. Generally, explosion or quarry blast generated travel-time data with known locations and origin times are useful for developing the path calibration parameters, but in many regions such data sets are scanty or do not exist. We present a method which is useful for regional path calibration independent of such data, i.e. with earthquakes, which is applicable for events down to M w = 4 and which has successfully been applied in India, central Asia, western Mediterranean, North Africa, Tibet and the former Soviet Union. These studies suggest that reliably determining depth is essential to establishing accurate epicentral location and origin time for events. We find that the error in source depth does not necessarily trade-off only with the origin time for events with poor azimuthal coverage, but with the horizontal location as well, thus resulting in poor epicentral locations. For example, hypocenters for some events in central Asia were found to move from their fixed-depth locations by about 20 km. Such errors in location and depth will propagate into path calibration parameters, particularly with respect to travel times. The modeling of teleseismic depth phases (pP, sP) yields accurate depths for earthquakes down to magnitude M w = 4.7. This M w threshold can be lowered to four if regional seismograms are used in conjunction with a calibrated velocity structure model to determine depth, with the relative amplitude of the P nl waves to the surface waves and the interaction of regional sPmP and pPmP phases being good indicators of event depths. We also found that for deep events a seismic phase which follows an S-wave path to the surface and becomes critical, developing a head wave by S to P conversion is also indicative of depth. The detailed characteristic of this phase is controlled by the crustal waveguide. The key to calibrating regionalized crustal velocity structure is to determine depths for a set of master events by applying the above methods and then by modeling characteristic features that are recorded on the regional waveforms. The regionalization scheme can also incorporate mixed-path crustal waveguide models for cases in which seismic waves traverse two or more distinctly different crustal structures. We also demonstrate that once depths are established, we need only two-stations travel-time data to obtain reliable epicentral locations using a new adaptive grid-search technique which yields locations similar to those determined using travel-time data from local seismic networks with better azimuthal coverage.

Mid mantle scatterers near the Mariana Slab detected with a double array method

We use a cluster of deep earthquakes, the fore‐ and aftershocks of the 23‐AUG‐1995 Mw=7.1 (18.8N, 145.3E, h=595 km) event in the Mariana subduction zone as source array to locate where waves scatter near the deep slab. In order to obtain the high‐precision location needed in this context, we first relocate the events with a modified master event technique. Using the double beam method on the relocated events and data from the Warramunga array in Australia, we identified two non‐standard S‐to‐P conversions arriving about 20.5 and 24 s after the P‐wave. The corresponding scatterers are approximately located at a depth of 790 km (720 km) and a distance of 0.9° to the southeast (2.3° to the southwest) of the main shock. The scatterers positions correspond to the location of lithosphere subducted below the 660 km discontinuity.

Spatial distribution of focal mechanisms for interplate and intraplate earthquakes associated with the subducting Pacific plate beneath the northeastern Japan arc: A triple‐planed deep seismic zone

The northeastern Japan arc is located in one of the most seismically active subduction zones in the world. In this study, we relocated hypocenters and determined focal mechanisms of small earthquakes (M≤5) beneath the arc in order to investigate in detail the stress distribution in and around the descending oceanic plate. In the hypocenter relocation we adopted a “source region station correction method” in which station corrections vary with hypocenter locations. We have developed a new focal mechanism determination technique named “master solution method,” which is analogous to the “master event method” in hypocenter determination. We applied the method to P and SH wave amplitude data to obtain 1106 focal mechanism solutions. From the new mechanism solutions and relocated hypocenters we found that there occur both low‐angle thrust fault (LT) type and downdip compression (DC) type earthquakes at depths from 40 to 70 km near the aseismic front; the DC type events are underlying the LT‐type events. Almost all the earthquake clusters are composed of LT‐type events. The western limit of the region where LT‐type events have occurred is subparallel to the trench axis, although it undulates considerably; it delineates the westernend of the active region of interplate seismicity. Furthermore, we found that normal fault (NF) type events also occur at depths from 70 km in the upper plane of the double‐planed deep seismic zone, which is characterized mainly by DC‐type event. These NF‐type events are distributed only in a thin uppermost portion of the slab close to the plate boundary. Below these, in the lower plane, are downdip extension (DE) type events. This result indicates that the deep seismic zone in the northeastern Japan arc is not double‐planed but triple‐planed, even beneath the land area, which cannot be explained by any simple models.

Precise Relative Location of 25-ton Chemical Explosions at Balapan Using IMS Stations

Wetest how well low-magnitude(m bLg 1.8 to 2.6), 25-ton chemical explosions at Balapan, Kazakhstan, can be located using IMS stations and standard earth models, relying on precisely determined relative arrival times of nearly similar, regional and teleseismic waveforms. Three 1997 Balapan explosions were recorded by a number of currently reporting and surrogate IMS stations. Three regional stations and two teleseismic arrays yielded consistent waveforms appropriate for relative picking. Master-event locations based on the AK135 model and ground-truth information from the first, shallowest and best-recorded explosion, fell under 1 km from known locations, for depths constrained to that of the master event. The resulting 90% confidence ellipses covered 12-13 km2and contained the true locations; however, results for depth constrained to true depth were slightly less satisfactory. From predictions based on ground truth, we found a Pgcoda phase at Makanchi, Kazakhstan to be misidentified and poorly modeled. After accounting for this, 90% ellipses shrank to 2-3 km2and true-depth mislocation vectors became more consistent with confidence-ellipse orientations. These results suggest that a high level of precision could be provided by a tripartite array of calibration shots in cases where models are poorly known. We hope that the successful relocation of these small Balapan shots will support the role of calibration explosions in verification monitoring and special event studies, including on-site inspection.

Broadband source modeling of the November 8, 1997, Tibet (Mw= 7.5) earthquake and its tectonic implications

We studied the source process of a large (Ms= 7.9) intraplate earthquake that occurred on November 8, 1997, at 1002 UT in a remote region of northern Tibet. We used four distinct methods to investigate the broadband source process and thereby better understand the tectonic implications of this event. We relocated aftershocks using a master event technique and found that the distribution of aftershocks covers a region of 200 km in lateral extent. We also employed a surface wave spectral inversion technique to estimate the mainshock moment, depth, centroid location, and centroid time and utilized an empirical Green's function technique to extract rupture directivity information and a detailed source time function from observed seismograms. We also inverted body waves to estimate the moment release along the fault and the source time function. The 1997 earthquake ruptured a strike‐slip fault that appears to be an extension or splay of the Kun Lun fault system. This fault is one of the most seismically active strike‐slip faults within the Tibetan plateau and has had events with surface wave magnitudes of 6.1, 7.4, and 7.9 in this region since 1973. The rupture released most of the energy within the first 20 s and propagated bilaterally initially, with the later rupture propagating westward for 20–30 s. The absence of large aftershocks suggests that the earthquake efficiently released the stored strain. Comparing mainshock to the largest aftershock energy ratios for this event and other large strike‐slip events shows that faulting within the plateau has the characteristics of weak faults (e.g., fracture zone faulting).

A Temporary Network For Seismological Monitoring In West-Saxony: First Results

Since December 1997 a network of 10 autonomously recording digital seismic stations operates in W-Saxony to monitor microseismic activity generated by tectonic movements in the Gera-Jachymov fault zone and induced by the flooding of the uranium mining area near Aue. Further goals to be followed with these data are the in situ verification of engineering seismological parameters and the study of the transmission properties of seismic waves across the Gera-Jachymov fault zone to improve seismic risk evaluation. So far 19 tectonic and more than 50 induced events have been located and source parameters have been determined. Event clusters near Zwickau and within the Aue mining area could be spatially resolved with a master event technique. The cluster near Zwickau occured on a common fault plane striking parallel to the Gera-Jachymov fault zone and dipping at an angle of about 60° towards ENE. The induced events near Aue occured within a volume of approximately 5 km 3 . The majority of these events were located in the granite body underneath the mining area. Fault plane solutions show a variety of focal mechanisms with no clear relation to the regional stress field.

A detailed analysis of two seismic sequences in Abruzzo, Central Apennines, Italy

A three-component digital seismic network has been installed along central Apennines since the end of 1991. Two seismic sequences having main shocks of magnitudes 3.9 and 3.7 were recorded in August 1992 and June 1994, respectively. A detailed analysis of these sequences, including multiplet relocation, fault-plane solutions and source parameter estimation, is performed in the present paper. A correlation analysis allowed us to recognize a number of correlated events in the two sequences which were used for relative locations using a master event technique. This analysis allowed to obtain a better alignment of epicentral data along two almost orthogonal directions, following an Apenninic and an anti-Apenninic trend. For the two sequences, fault-plane solutions were evaluated by using a first arrival technique, resulting in mechanisms with predominant normal faulting for the 1992 and 1994 swarms. S-wave polarization analysis allowed to check the stability of the previous solutions and to reduce their range of uncertainty. The same technique was also applied to derive the composite fault-plane solutions from the aftershocks, resulting in solutions which are in good agreement with those derived from the main shocks of both sequences. Source parameters were then derived from the three-component records of 28 well-recorded events with seismic moment in the range 8.5 × 1010–1.0 × 1014 Nm. Stress drops ranged in the interval 0.3–52.3 bar and source radii were of the order of 100 m. Their scaling relations are in good agreement with other results derived from the analysis of other Italian earthquakes that occurred in regions of predominantly normal faulting tectonics (Apennines and Calabrian arc).

Analysis on the master event method and precise location of 1997 Jiashi strong earthquake swarm in western China

Master event location method was described in detail in this paper. Some problems in the application of master event method have been analyzed and some improvements of the method have been made. As compared the location results of M S≥3.0 earthquakes of Jiashi swarm obtained by using this method with that by the traditional absolute method, the result obtained by using the master event method shows more reasonable and more consistent with that from the focal mechanism solutions. After relocation, we can see, the epicenters of M≥5.0 earthquakes show an echelon-type alignment along NNW-SSE direction, and all earthquakes concentrate nearly in a volume region about 30 km (N-S)×15 km (E-W)×15 km (U-D). Earthquake focal depths are mainly in the range of 15–28 km.

Suppression of tumorigenicity in an aggressive cervical carcinoma induced by protein zero, a nervous system IgCAM.

In mammals, protein zero (P0), a neural IgCAM, is expressed solely in the peripheral nervous system where it mediates self-adhesion of Schwann cell membranes as compact myelin is generated. We show that when P0 is expressed in HeLa, a cervical carcinoma cell line, cells regain adhesion-mediated growth control, including the acquisition of contact inhibition and loss of anchorage-independent growth. Additionally, P0-expressing HeLa cells lose the ability to invade an artificial matrix, which correlates with decreased secretion of matrix-degrading enzymes. Lastly, and of great interest, unlike the aggressively metastatic cell line from which they were derived, P0-HeLa cells are neither tumorigenic nor metastatic when injected into athymic nude mice. By all these criteria, P0 expression appears to efficiently suppress in the long term, the transformed state of this carcinoma cell line. N-cadherin and its intracellular partners plakoglobin, alpha- and beta-catenin were significantly upregulated in the P0-HeLa cells. It appears therefore that P0 induces epithelialization and suppression of tumorigenicity in HeLa through the activation of the cadherin/catenin signaling systems. We conclude that the forced expression of bona fide adhesion molecules, such as P0, may serve as 'upstream' inducers of an essentially dormant but undamaged adhesion program in carcinoma cells that ultimately triggers the re-acquisition of normal epithelial characteristics, thereby suppressing tumorigenicity. Therapeutically, it may be that intercellular adhesion, no matter how it is induced, may serve as a single master event that is able to induce reversion of the carcinomatous state.

The use of waveform similarity to define planes of mining-induced seismic events

Mining-induced seismicity results from a complex interaction of ambient and mining-induced stresses acting on a rock mass that has been intersected by a variety of geological weaknesses and discontinuities. A major challenge is to improve mine design methodology by identifying the geological features that are seismically active and then changing the direction of mining to reduce the potential for shear slip on these features. In this paper we classify seismic events with similar waveforms (doublets) into multiplets, relocate them simultaneously using arrival-time differences based on cross-correlations between all event pairs and then identify the orientation of the most likely plane on which the events are located. Identification of multiplets has been automated, even including events that have not previously been located. In contrast to the conventional `master' event method, no single master event is used: each event is a `master' event for each other event. The absolute location of each multiplet is stabilised by using all manually selected arrival times. Vectors are drawn between all pairs of events and Principal Component Analysis applied to obtain the orientation of the most likely plane of the events in each multiplet. We tested this method on seismic data recorded underground at a site in Blyvooruitzicht Gold Mine, South Africa, in which a strike stabilising pillar has been mined from one end with the aid of precondition blasting. We found that 39% of events that were previously located in a diffuse cloud within a mine pillar, were formed into three distinct multiplets. Two multiplets were oriented parallel to directions of dominant mining-induced stresses, i.e., along the long axis of the pillar and parallel to the active mining face, and the third along a pervasive joint set.

On the inversion of Sd particle motion for seismic anisotropy in D'

In order to make accurate estimates of anisotropy in D', as measured from observations of Sdi f f (Sd) it is necessary to correct the observed waveforms for anisotropy outside of the deepest mantle as well as side refraction along the path, and to pick arrivals of SVd and SHd as accurately as possible. We show that corrections based on estimates of upper mantle anisotropy inferred from SKS/SKKS splitting measurements are sometimes insufficient and propose a master event method to directly obtain more accurate corrections on specific source‐station paths. Our study illustrates the complexity of structure that needs to be taken into account when addressing issues of D' properties using seismic body wave methods. We also describe a method to accurately measure the arrival time of the corrected SV d wave.

The June 12, 1995 microearthquake sequence in the city of Rome 1167

The earthquake of June 12, 1995 has been located using local and regional data (41°48.8'N, 12°30.8°6E at a depth of about 11.5 km) a few kilometers inside the city limit of Rome, in its southernmost part. This is the first event that occurred in Rome for which instrumental data are available. The local magnitude estimated from digital recordings is ML 3.6 and it was largely felt reaching intensity VI MCS. We constrained the focal mechanism by analyzing the S-wave polarization and it agrees well with the distribution of P-wave polarities. The fault plane solution shows a dominant strike slip mechanism (strike 275°, dip 70°, rake - 140°). Seismic moment, M0 = 2.3 ± 0.6 1021dyne × , was computed from S-wave displacement spectra of horizontal components of ground motion digital waveforms. The corresponding source radius ranges between 200 and 500 m, depending on the assumed stress drop (100 bars or 10 bars, respectively). The earthquake was preceded by a ML 2.6 foreshock. The seismic sequence lasted a few days during which 38 aftershocks were recorded. The seismicity pattern shows the characteristics of a mainshock-aftershock sequence, rather than swarm behavior which seems to characterize the activity of the neighboring seismogenic areas of the Alban Hills. We used a master event algorithm to locate some of the aftershocks. Results show that the relocated aftershocks are clustered in a small volume in proximity of the mainshock hypocenter.

Applying the relative hypocentre location approach: where was the 1980 November 23 Irpinia earthquake?

The purpose of this work is to evaluate under what conditions it is feasible and with what accuracy it is possible to locate the nucleation point of a large earthquake, given the availability of aftershocks located with high precision by the deployment of a local network. We experiment with several approaches and apply them lo the location of the epicentre of the 1980 November 23 Irpinia earthquake (Mw= 6.9). First we use local Pg phases selected to optimize the azimuthal coverage, obtaining a well-constrained location with a small statistical error, which typically underestimates the true hypocentre uncertainty. We then exploit the relative location technique, obtaining stable, almost coincident solutions under three conditions: (1) using multiple independent master events to derive an average epicentre; (2) fitting simultaneously the larger data set for all available master events, using a forward approach; (3) conducting an a priori evaluation of the statistics of station and master events to separate model uncertainties and improve the statistical accuracy of the relative locations. Moreover, only by introducing station statistics can we achieve the desired accuracy of ≅ 1 km in constraining the rupture nucleation point of this large earthquake, and we show that the application of the relative location technique to uncleaned, unweighted data for a single master event provides only a crude epicentre with a confidence ellipse deceivingly smaller than the true hypocentre uncertainty. The revised epicentre for the 1980 November 23 Irpinia earthquake (48.803 °N-15.302°E) validates the class of multidisciplinary reconstructions of the source process such as the model of Valensise et al. (1989), based on the hypocentre of Westaway & Jackson (1987), and is shifted by almost 13 km to the NW of the epicentre recently proposed by Westaway (1992).

Non‐double‐couple focal mechanisms in an oceanic, intraplate earthquake swarm: Application of an improved method for comparative event, moment tensor determination

Between February 1991 and May 1992, an earthquake swarm including 33 teleseismically recorded events occured about 300 km west of the axis of the southern East Pacific Rise. Joint hypocentral relocations show that the best located events were in a 10‐km‐wide band between and parallel to two seamount chains. New, simulated‐annealing inversion procedures were developed to find the moment tensors of three of the largest events that then served as master events for focal mechanism determination of the smaller events. Path/station corrections were applied to the spectra of surface waves from the smaller events, and the corrected spectra were linearly inverted for the moment tensors. The new procedures made it possible to derive focal mechanisms for 32 of the 33 earthquakes, ranging in size from Mw 4.2 to 5.9. All of the events have double‐couple components that are nearly pure normal faulting with a wide range of strikes of the nodal planes. Most have a non‐double‐couple component that may have been caused by simultaneous slip on nearly randomly oriented fault planes. The individual mechanisms and net horizontal extension that is nearly equal in all directions are consistent with the release of thermal stresses in the cooling oceanic lithosphere.

Microearthquake analysis for hydraulic fracturing process

The hydraulic fracture technique is widely applied in the enhancement of petroleum and natural gas productions and in the development of geothermal energy. This technique is also used to create an underground fracture zone system for disposal of solid and liquid wastes. This is the most recent development in the application of industrial techniques to environmental protection scientific problems. Knowledge of mechanical properties and geometrical parameters of a hydraulic fracture zone is important for both energy resource development and safe disposal of waste. Hydraulic fracturing often induces many microearthquakes. Analysis of the spatial-temporal distribution of the induced seismicity yields the geometry of a hydraulic fracture zone, and kinetic and dynamic parameters associated with the fracture growth process. Applying a waveform correlation analysis and a space-time grid search method, we precisely determined hypocentral locations for 157 microearthquakes induced by hydraulic fracturing. Spatial distribution of the induced seismicity clearly shows the dimension and orientation of a hydraulic fracture zone. Variation of the seismicity distribution in time and space was used to infer the growth rate and direction of the fracture zone. An empirical Green’s function (EGF) method was applied to earthquake doublets to retrieve relative source time functions (RSTF’s) and to estimate source parameters, such as seismic moment, source radius, and stress drop, for larger microearthquakes. Azimuthal variation of the RSTF of a master event indicates that the source ruptured to the northwest, which aggrees with the fracture zone growth direction. Large variation of stress drops for these induced earthquakes reflects the significant heterogeneity of mechanical properties in the hydraulic fracture zone.