scholarly journals Slip distribution of the 19 September 1985 Michoacan, Mexico, earthquake: Near-source and teleseismic constraints

1989 ◽  
Vol 79 (3) ◽  
pp. 655-669 ◽  
Author(s):  
Carlos Mendoza ◽  
Stephen H. Hartzell
Keyword(s):  
Time Window ◽  
Source Region ◽  
Strong Motion ◽  
Strike Slip ◽  
Inversion Method ◽  
Data Sets ◽  
Aftershock Activity ◽  
Waveform Data ◽  
Simultaneous Inversion ◽  
Mexico Earthquake

Abstract We simultaneously invert the strong-motion velocity records and the long- and intermediate-period teleseismic P waveforms of the 19 September 1985 Michoacan, Mexico, earthquake to recover the distribution of slip on the fault using a point-by-point constrained and stabilized, least-squares inversion method. A fault plane with strike fixed at 300° and dip fixed at 14° is placed in the region of the earthquake hypocenter and divided into 120 subfaults. Rupture is assumed to propagate at a velocity of 2.6 km/sec away from the hypocenter. Synthetic near-source ground motions and teleseismic P waveforms for pure strike-slip and dipslip dislocations are calculated for each subfault. The observed data are then inverted to obtain the amount of strike-slip and dip-slip displacement required of each subfault. We also invert the data sets using a time-window procedure where the subfaults are allowed to slip up to three times. This approach relaxes the constraint of fixed subfault rupture time imposed by a constant rupture velocity. Inversion of the strong-motion data alone yields a slip model similar to the solution previously obtained using only teleseismic waveforms. This result supports the use of teleseismic waveform data for the derivation of fault dislocation models in the absence of strong-motion recordings. Our simultaneous inversion of both data sets suggests that rupture during the Michoacan earthquake was controlled largely by the failure of three major asperities located along the length and down the dip of a 150-km segment of the Cocos-North America plate boundary. The solution contains three major source regions including an 80 km by 55 km source near the hypocenter with a peak slip of 6.5 meters. Two additional sources are present on the southeast portion of the fault about 70 km away from the hypocenter. One of these sources, with a peak slip of 5 meters, covers a 45 km by 60 km area and extends downdip from a depth of about 10 km to 24 km. The third source region is somewhat smaller (30 km by 60 km area, 3.1-meters peak slip) and extends further downdip at depths between 27 km and 39 km. Aftershock activity following the earthquake was associated mainly with the two shallow sources. These two sources are separated by the aftershock zone of the 1981 Playa Azul earthquake.

Spatial distribution of high-frequency energy radiation on the fault of the 1995 Hyogo-Ken Nanbu, Japan, earthquake (MW 6.9) on the basis of the seismogram envelope inversion

1999 ◽  
Vol 89 (1) ◽  
pp. 22-35 ◽  
Author(s):  
Hisashi Nakahara ◽  
Haruo Sato ◽  
Masakazu Ohtake ◽  
Takeshi Nishimura
Keyword(s):  
Spatial Distribution ◽  
Wave Energy ◽  
High Frequency ◽  
Fault Plane ◽  
Time Window ◽  
Source Region ◽  
Inversion Method ◽  
S Wave ◽  
Energy Radiation ◽  
Initial Rupture

Abstract We studied the generation and propagation of high-frequency (above 1 Hz) S-wave energy from the 1995 Hyogo-Ken Nanbu (Kobe), Japan, earthquake (MW 6.9) by analyzing seismogram envelopes of the mainshock and aftershocks. We first investigated the propagation characteristics of high-frequency S-wave energy in the heterogeneous lithosphere around the source region. By applying the multiple lapse time window analysis method to aftershock records, we estimated two parameters that quantitatively characterize the heterogeneity of the medium: the total scattering coefficient and the intrinsic absorption of the medium for S waves. Observed envelopes of aftershocks were well reproduced by the envelope Green functions synthesized based on the radiative transfer theory with the obtained parameters. Next, we applied the envelope inversion method to 13 strong-motion records of the mainshock. We divided the mainshock fault plane of 49 × 21 km into 21 subfaults of 7 × 7 km square and estimated the spatial distribution of the high-frequency energy radiation on that plane. The average constant rupture velocity and the duration of energy radiation for each subfault were determined by grid searching to be 3.0 km/sec and 5.0 sec, respectively. Energy radiated from the whole fault plane was estimated as 4.9 × 1014 J for 1 to 2 Hz, 3.3 × 1014 J for 2 to 4 Hz, 1.5 × 1014 J for 4 to 8 Hz, 8.9 × 1012 J for 8 to 16 Hz, and 9.8 × 1014 J in all four frequency bands. We found that strong energy was mainly radiated from three regions on the mainshock fault plane: around the initial rupture point, near the surface at Awaji Island, and a shallow portion beneath Kobe. We interpret that energetic portions were associated with rupture acceleration, a fault surface break, and rupture termination, respectively.

Classification of Main Shocks and Aftershocks in the NGA-West2 Database

2014 ◽  
Vol 30 (3) ◽  
pp. 1257-1267 ◽  
Author(s):  
Kathryn E. Wooddell ◽  
Norman A. Abrahamson
Keyword(s):  
Time Window ◽  
Strong Motion ◽  
Data Sets ◽  
Horizontal Distance ◽  
Strong Motion Data ◽  
Motion Data ◽  
Rupture Plane ◽  
Main Shocks ◽  
Short Period ◽  
Surface Projection

Previous studies have found a systematic difference between short-period ground motions from aftershocks and main shocks, but have not used a consistent methodology for classifying earthquakes in strong motion data sets. A method for unambiguously classifying earthquakes in strong motion data sets is developed. The classification is based on the Gardner and Knopoff time window, but with a distance window based on a new distance metric, CRJB, defined as the shortest horizontal distance between the centroid of the surface projection of the potential aftershock rupture plane and the surface projection of the main shock rupture plane. Class 2 earthquakes are earthquakes that have a CRJB distance less than a selected limit and within a time window appropriate for aftershocks. All other earthquakes are classified as Class 1. For maximum CRJB of 0 km and 40 km, 11% and 36% of the earthquakes in the NGA-West2 database are Class 2 events, respectively.

Simultaneous Joint Migration Inversion with calendar-time constraints as a processing tool for semi-continuous surveys

Geophysics ◽  
2021 ◽  
pp. 1-90
Author(s):  
Shan Qu ◽  
Eric Verschuur
Keyword(s):  
Low Cost ◽  
Time Lapse ◽  
Time Constraints ◽  
Inversion Method ◽  
Data Sets ◽  
Time Axis ◽  
Calendar Time ◽  
Full Field ◽  
Simultaneous Inversion ◽  
Frequent Monitoring

Nowadays, to obtain a better understanding of dynamic time-lapse changes, frequent seismic monitoring is necessary, although it will generate a considerable cost increase. Therefore, low-cost frequent monitoring, e.g., sparse and/or nonrepeated surveys, is desired. The simultaneous inversion-based method allows the baseline and monitor parameters to communicate and compensate with each other during inversion via constraints and helps to reduce the artifacts caused by sparse acquisition. These features make it largely independent of the used low-cost acquisition geometry and suitable for inexpensive frequent monitoring surveys. Therefore, we have used this simultaneous inversion-based method as an effective time-lapse processing tool for data sets acquired from inexpensive, semicontinuous time-lapse monitoring surveys, which are based on the so-called instantaneous 4D (i4D) technology. We choose a specific simultaneous inversion method called simultaneous joint migration inversion (S-JMI), which combines a simultaneous processing strategy with the JMI method. In i4D technology, inexpensive localized/sparse surveys, called i4D surveys, are deployed frequently between the conventional full-field surveys. This technology can be treated as a special case of changing geometries during monitoring. In this case, the simultaneous strategy allows the information of the full-field survey to compensate for the insufficient illumination of the localized/sparse i4D surveys during processing. Furthermore, we apply constraints on the reflectivity and velocity differences between the baseline and monitor vintages along the calendar-time axis called calendar-time constraints. These constraints take advantage of the feature that time-lapse effects develop (semi)continuously along the calendar-time axis, when the monitoring surveys are deployed (semi)continuously over calendar time. Based on a complex synthetic example, we determined that S-JMI is a promising tool to process the data sets from the semicontinuous monitoring surveys based on i4D technology. Finally, we found that the calendar-time constraints significantly improve the quality of time-lapse effects.

scholarly journals The October 9, 1996 earthquake in Cyprus: seismological, macroseismic and strong motion data

1999 ◽  
Vol 42 (1) ◽  
Author(s):  
I. Kalogeras ◽  
G. Stavrakakis ◽  
K. Solomi
Keyword(s):  
Eastern Mediterranean ◽  
Strong Motion ◽  
Strike Slip ◽  
Reverse Fault ◽  
Aftershock Activity ◽  
Motion Data ◽  
Attenuation Relationships ◽  
Largest Aftershock ◽  
Sea Area ◽  
Development Department

On October 9, 1996, an earthquake of magnitude 6.8 occurred in the sea area SW of Cyprus, Eastern Mediterranean. This earthquake, which caused damage mostly in the area of Paphos and Limassol, triggered an accelerograph installed at Yermasoyia dam, north of Limassol. The Geodynamic Institute of the National Observatory of Athens in cooperation with the Geological Survey of Cyprus deployed five digital accelerographs in order to record large aftershocks. Although the aftershock activity lasted over four months and included a large number of earthquakes with magnitudes 4.5 and greater, only the largest aftershock of January 13, 1997, having a magnitude of 5.9, triggered two of these five accelerographs. Moreover another digital accelerograph, operated by the Water Development Department of Cyprus, was triggered and this record was also taken into account in this study. The first Cyprean strong motion records obtained to date, gave us the opportunity to compare the results from their analysis to the already proposed attenuation relationships from other areas of the world with a similar seismotectonic regime. Although a general fitting to the attenuation curves for subduction events and strike-slip/reverse fault events was found, the calculated peak ground accelerations were found to be lower than others. Unfortunately, due to the lack of data from previous Cyprean earthquakes, it was not possible to conclude to precise attenuation

scholarly journals Updated determination of earthquake magnitudes at the Swiss Seismological Service

2020 ◽  
Author(s):  
Roman Racine ◽  
Carlo Cauzzi ◽  
John Clinton ◽  
Donat Fäh ◽  
Benjamin Edwards ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Source Region ◽  
Strong Motion ◽  
Velocity Model ◽  
Seismic Network ◽  
Event Processing ◽  
Waveform Data ◽  
Data Archiving ◽  
Short Period ◽  
Magnitude Determination

<p>The Swiss Seismological Service (SED; http://www.seismo.ethz.ch) at ETH Zürich is the federal agency in charge of monitoring earthquakes in Switzerland and neighboring areas, and for the assessment of seismic hazard and risk for the region. The SED seismic network largely relies on software and databases integrated in the SeisComP3 monitoring suite for waveform acquisition, automatic and manual event processing, event alerting, web infrastructure, data archiving and dissemination. Data from all digital seismic stations acquired by the SED over the last 30 years - broadband (presently ~230), strong-motion (~185), short-period (~65), permanent and temporary - are homogeneously integrated in the seismic network processing tools and products. Waveform data from the Swiss National Seismic Networks are openly available through the SED website and ORFEUS EIDA / Strong-Motion (http://orfeus-eu.org/data/) data gateways. The SED earthquake catalogue is publicly available through FDSN Event web services at  the SED (http://arclink.ethz.ch/fdsnws/event/1/). The Swiss seismic hazard maps are integrated in the EFEHR portal (http://www.efehr.org). The SED is updating its strategy for magnitude determination to make it fully consistent with the state-of-the-art in engineering seismology and seismic hazard studies in Switzerland, and to optimise the use of its dense seismic monitoring infrastructure. Among the planned changes are the: (a) adoption of a new ML relationship applicable in the near-source region at epicentral distances smaller than 15-20 km; (b) inclusion of ML station corrections based on empirically observed (de)amplification with respect to the Swiss reference rock velocity model and associated predictions; (c)  seamless computation of Mw based on spectral fitting of recorded FAS using a Swiss specific model. In this contribution we present and discuss the updated magnitude computations for a playback dataset of thousands of recorded earthquakes, and compare them with the current official estimates. We discuss the expected impacts of the new magnitude determination strategy on the SED event processing chain in SeisComP3, the SED catalogues and other seismological products. We welcome community feedback on our planned transition strategy.</p>

scholarly journals The slip history of the 1994 Northridge, California, earthquake determined from strong-motion, teleseismic, GPS, and leveling data

1996 ◽  
Vol 86 (1B) ◽  
pp. S49-S70 ◽  
Author(s):  
David J. Wald ◽  
Thomas H. Heaton ◽  
K. W. Hudnut
Keyword(s):  
Strong Motion ◽  
Geodetic Data ◽  
Body Waves ◽  
Dislocation Model ◽  
Data Sets ◽  
Frequency Content ◽  
Motion Velocity ◽  
S Wave ◽  
Waveform Data ◽  
Slip History

Abstract We present a rupture model of the Northridge earthquake, determined from the joint inversion of near-source strong ground motion recordings, P and SH teleseismic body waves, Global Positioning System (GPS) displacement vectors, and permanent uplift measured along leveling lines. The fault is defined to strike 122° and dip 40° to the south-southwest. The average rake vector is determined to be 101°, and average slip is 1.3 m; the peak slip reaches about 3 m. Our estimate of the seismic moment is 1.3 ± 0.2 × 1026 dyne-cm (potency of 0.4 km3). The rupture area is small relative to the overall aftershock dimensions and is approximately 15 km along strike, nearly 20 km in the dip direction, and there is no indication of slip shallower than about 5 to 6 km. The up-dip, strong-motion velocity waveforms are dominated by large S-wave pulses attributed to source directivity and are comprised of at least 2 to 3 distinct arrivals (a few seconds apart). Stations at southern azimuths indicate two main S-wave arrivals separated longer in time (about 4 to 5 sec). These observations are best modeled with a complex distribution of subevents: The initial S-wave arrival comes from an asperity that begins at the hypocenter and extends up-dip and to the north where a second, larger subevent is centered (about 12 km away). The secondary S arrivals at southern azimuths are best fit with additional energy radiation from another high slip region at a depth of 19 km, 8 km west of the hypocenter. The resolving power of the individual data sets is examined by predicting the geodetic (GPS and leveling) displacements with the dislocation model determined from the waveform data, and vice versa, and also by analyzing how well the teleseismic solution predicts the recorded strong motions. The general features of the geodetic displacements are not well predicted from the model determined independently from the strong-motion data; likewise, the slip model determined from geodetic data does not adequately reproduce the strong-motion characteristics. Whereas a particularly smooth slip pattern is sufficient to satisfy the geodetic data, the strong-motion and teleseismic data require a more heterogeneous slip distribution in order to reproduce the velocity amplitudes and frequency content. Although the teleseismic model can adequately reproduce the overall amplitude and frequency content of the strong-motion velocity recordings, it does a poor job of predicting the geodetic data. Consequently, a robust representation of the slip history and heterogeneity requires a combined analysis of these data sets.

scholarly journals Simultaneous Rupture on Conjugate Faults During the 2018 Anchorage, Alaska, Intraslab Earthquake (MW 7.1) Inverted from Strong-Motion Waveforms

2020 ◽  
Author(s):  
Yujia Guo ◽  
Ken Miyakoshi ◽  
Masato Tsurugi
Keyword(s):  
Subduction Zone ◽  
Ground Motion ◽  
Source Parameters ◽  
Source Region ◽  
Rare Event ◽  
Strong Motion ◽  
North American Plate ◽  
Aftershock Activity ◽  
Intraslab Earthquake ◽  
Simultaneous Rupture

Abstract An MW 7.1 intraslab earthquake within the Pacific/Yakutat slab underlying the North American Plate struck Anchorage, southern Alaska, on November 30, 2018. The ground-motion records very close to the source region of the Anchorage earthquake provide an important opportunity to better understand the source characteristics of intraslab earthquakes in this subduction zone. We estimated the kinematic rupture process during this earthquake using a series of strong-motion waveform (0.05–0.4 Hz) inversions. Our inversions clearly indicate that the Anchorage earthquake was a rare intraslab event with simultaneous rupture on two conjugate faults, which are worldwide recognized sometimes for shallow crustal earthquakes but rarely for deep intraslab earthquakes. Interestingly, one of the conjugate faults is located in a zone that had low aftershock activity. This fault extends to great depth and may reflect a deep oceanic Moho or a local low-velocity and high-VP/VS zone within the oceanic mantle. Even though the Anchorage earthquake was a rare event due to the conjugate faults, we found that its kinematic source parameters were not abnormal compared to the average parameters of global intraslab earthquakes. The normal source parameters suggest that the larger low-frequency (0.33-Hz) ground-motion amplitudes than predicted by the ground-motion prediction equation observed in downtown Anchorage were primarily due to site amplification effects associated with a sedimentary basin, not source effects. Because such normality of the source parameters was also found for another large intraslab earthquake in the subducting Pacific/Yakutat slab, this normality is likely an important source characteristic common to this subduction zone.

The Waveform Characteristics and Classification of Intermediate-depth Earthquakes in Ryukyu Subduction Zone

2020 ◽  
Author(s):  
Yu-Jhen Lin ◽  
Tai-Lin Tseng ◽  
Wen-Tzong Liang
Keyword(s):  
Subduction Zone ◽  
High Frequency ◽  
Time Window ◽  
Source Region ◽  
Focal Depth ◽  
Low Frequency ◽  
Frequency Content ◽  
Low Velocity ◽  
Waveform Data ◽  
Intermediate Depth

<p>Using intraslab earthquakes shallower than 150 km in the southernmost Ryukyu subduction zone, previous studies in Taiwan found the wave guide effect that typically shows a low-frequency (<2Hz) first P arrival followed by sustained high-frequency (3–10 Hz) wave trains. Recently occurred deeper events at depth 150-300 km allow us to better quantify the properties of those seismic waves traveling in the subduction zone. In this study, we aim to systematically scan through the local broadband waveforms of the intermediate depth earthquakes with M>5 between 1997 and 2016. Event are classified based on the waveform characteristics and their frequency contents.</p><p>To detect events with similar properties, we applied sliding-window cross-correlation (SCC)​ using three components of P waveform data simultaneously for a set of stations​. The time window used here was 10 s and traces were bandpass filtered in the frequency range 0.5–10 Hz. After the degree of similarity are calculated, e​vents containing comparable waveforms can be sorted into families. The events within a family would have been triggered because they came from the same source region and their paths to a particular receiver should produce similar waveforms. Our results show that most earthquakes are low in waveform similarity, implying no “repeating” behavior for those intermediate intraslab events. However, some events (cc>0.6 threshold) present enough charterers that can be grouped as a family.</p><p>One important property is the frequency content of the arrivals that may be related to the speed of structure traveled. We have developed a work scheme to determine the delayed time of higher-frequency energy. On family of events show beautiful dispersion with arrival time smoothly increasing with frequency between 0.5 and 6 Hz.​ Another type of dispersive waveforms appear as two distinct arrivals: low frequency and then high-frequency energy, separated by around 1 s. The time delay seems to be independent of focal depth. The latter case has been reported in the previous study for shallower event and it was interpreted as effect from low-velocity layer or heterogeneity of the subducted slab. On the other hand, the continuous dispersion is a new feature observed by our study, which may infer a thinner layer and/or longer propagation for some kind of reflecting waves to develop such interference.</p><p>In addition, we will classify the waveforms according to the frequency content and decay of coda. The variations in P coda properties can be associated with the way in which the seismic energy gets ducted into the stochastic waveguide associated with the lithosphere. With sufficient amount of data, it is possible to further identify the earthquakes with unusual source properties or structure anomaly along specific propagation paths. We expect the classification results can provide a reference for future numerical simulation analysis. </p><p>Keywords: Ryukyu subduction zone, SCC, guide wave, waveform classification, intermediate-depth earthquakes</p>

Rupture process of the 1980 Izu-Hanto-Toho-Oki earthquake deduced from strong motion seismograms

1988 ◽  
Vol 78 (3) ◽  
pp. 1074-1091
Author(s):  
Minoru Takeo
Keyword(s):  
Seismic Moment ◽  
Fault Plane ◽  
Near Field ◽  
Source Region ◽  
Vertical Plane ◽  
Strong Motion ◽  
Rupture Process ◽  
Japan Meteorological Agency ◽  
Inversion Method ◽  
Total Seismic Moment

Abstract The 1980 Izu-Hanto-Toho-Oki earthquake is studied in detail using near-field strong motion seismograms recorded at Japan Meteorological Agency stations. A seismogram inversion method is applied to deduce the dislocation distribution and the character of rupture propagation during this earthquake. This earthquake involves left-lateral strike-slip motion on the almost vertical plane with a strike of N10°W. The fault plane is shallower than about 12 km in depth, and the length is about 20 km. The large dislocation (large seismic moment) occurs near the hypocenter and at the southern end of the fault plane. The rupture propagates southward from the central part of the fault plane and spreads to the shallow area of the northern part of the fault plane after a delay of about 5 sec relative to the initiation of this earthquake. The total seismic moment is about 7 ×1025 dyne·cm. The aftershocks of magnitude equal to or greater than 4.0 take place in the areas where high stresses are expected to remain after this earthquake. The mechanical weakness of small submarine monogenetic volcanoes which are located above the source region seems to affect the rupture process of this earthquake.

scholarly journals Determination of near-fault impulsive signals with multivariate naïve Bayes method

2021 ◽  
Author(s):  
Deniz Ertuncay ◽  
Giovanni Costa
Keyword(s):  
Naive Bayes ◽  
Strong Motion ◽  
Naïve Bayes ◽  
Strike Slip ◽  
Naive Bayes Classifier ◽  
Bayes Classifier ◽  
Naïve Bayes Classifier ◽  
Earthquake Physics ◽  
Near Fault ◽  
A Site

AbstractNear-fault ground motions may contain impulse behavior on velocity records. To calculate the probability of occurrence of the impulsive signals, a large dataset is collected from various national data providers and strong motion databases. The dataset has a large number of parameters which carry information on the earthquake physics, ruptured faults, ground motion parameters, distance between the station and several parts of the ruptured fault. Relation between the parameters and impulsive signals is calculated. It is found that fault type, moment magnitude, distance and azimuth between a site of interest and the surface projection of the ruptured fault are correlated with the impulsiveness of the signals. Separate models are created for strike-slip faults and non-strike-slip faults by using multivariate naïve Bayes classifier method. Naïve Bayes classifier allows us to have the probability of observing impulsive signals. The models have comparable accuracy rates, and they are more consistent on different fault types with respect to previous studies.

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