Estimating the Hypocenter and Mechanism of the August 15, 1991 Centre Hall, Pennsylvania Earthquake Using Single-Station Data

1992 ◽  
Vol 63 (4) ◽  
pp. 541-555 ◽  
Author(s):  
Robert H. Clouser
Keyword(s):  
Wave Dispersion ◽  
Velocity Model ◽  
P Wave ◽  
Digital Data ◽  
Source Depth ◽  
Axis Orientation ◽  
Station Data ◽  
Short Period ◽  
Single Station ◽  
Back Azimuth

Abstract On August 15, 1991 a small (mbLg = 3.0) earthquake occurred near the town of Centre Hall, Pennsylvania. Based on early reports of felt effects and earthquake-generated sounds, the epicenter was placed somewhere ENE of State College, Pennsylvania. Three-component short-period digital data from the DWWSSN station SCP were analyzed to determine the hypocenter. Often, for small earthquakes in regions without dense seismic networks, information about an event must be obtained from single-station data. In this case, since no shallow velocity model exists for the area, simple ideas of wave propagation are invoked to estimate the distance and back-azimuth to the event. The horizontal P-wave particle motion constrained the back-azimuth, after calibrating the horizontal components by measuring the back-azimuth of quarry blast P-waves of known location. Distance determination was hampered by lack of a detailed upper crustal velocity model. Using iterative forward waveform modeling, a velocity model was generated that fit the observed S-minus-P and Rg-minus-P times and Rg-wave dispersion, and which was consistent with known upper crustal velocities in the area. A source depth of less than 1 km was inferred from the Rg-to-S ratio, the depth phase sP, and reports of earthquake-generated sounds. Estimates of the focal mechanism were obtained by a grid search procedure using Green’s functions computed with wavenumber integration for shear dislocation sources. Theoretical and observed amplitudes of sP, direct SH and SV (taken as ratios to the direct P), along with P polarity were compared for all possible combinations of strike, dip, and rake. Though fault plane orientation is poorly constrained, E-W to WNW-ESE P-axis orientation is a robust result of the search. Normal-faulting mechanisms are inconsistent with the data. However, the theoretical SV-to-P ratio is up to a factor of two larger than the observed ratio. This is probably related to an inadequate structure model and waveform sensitivity to source depth. Mechanism P-axis trends are consistent with other regional stress field indicators in the area.

Estimates of velocity structure and source depth using multiple P waves from aftershocks of the 1987 Elmore Ranch and Superstition Hills, California, earthquakes

1991 ◽  
Vol 81 (2) ◽  
pp. 508-523
Author(s):  
Jim Mori
Keyword(s):  
Velocity Structure ◽  
Velocity Model ◽  
P Wave ◽  
Sediment Layer ◽  
Source Depth ◽  
Imperial Valley ◽  
P Waves ◽  
Main Shocks ◽  
Aftershock Sequences ◽  
Event Record

Abstract Event record sections, which are constructed by plotting seismograms from many closely spaced earthquakes recorded on a few stations, show multiple free-surface reflections (PP, PPP, PPPP) of the P wave in the Imperial Valley, California. The relative timing of these arrivals is used to estimate the strength of the P-wave velocity gradient within the upper 5 km of the sediment layer. Consistent with previous studies, a velocity model with a value of 1.8 km/sec at the surface increasing linearly to 5.8 km/sec at a depth of 5.5 km fits the data well. The relative amplitudes of the P and PP arrivals are used to estimate the source depth for the aftershock distributions of the Elmore Ranch and Superstition Hills main shocks. Although the depth determination has large uncertainties, both the Elmore Ranch and Superstition Hills aftershock sequences appear to have similar depth distribution in the range of 4 to 10 km.

A discrimination analysis of short-period regional seismic data recorded at Tonto Forest Observatory

1982 ◽  
Vol 72 (4) ◽  
pp. 1351-1366
Author(s):  
J. R. Murphy ◽  
T. J. Bennett
Keyword(s):  
Epicentral Distance ◽  
Test Site ◽  
P Wave ◽  
Set Cover ◽  
Spectral Amplitude ◽  
Nevada Test Site ◽  
Data Set ◽  
Short Period ◽  
Single Station ◽  
Regional Phases

abstract A new seismic discriminant based on spectral differences of regional phases from earthquakes and explosions recorded at a single station has been tested and found to work remarkably well. The test data consisted of a well-constrained set of 30 Nevada Test Site (NTS) explosions and 21 earthquakes located within about 100 km of NTS which were recorded on short-period seismographs at the Tonto Forest Observatory in central Arizona at an epicentral distance averaging 530 km. The events in the data set cover a magnitude range from 3.3 to 4.8 (mb) for which Pn, Pg, and Lg phases have been analyzed. We found that, although Lg phases from earthquakes are typically more prominent than for explosions with comparable P-wave amplitude levels, simple time-domain Lg/P amplitude ratios do not result in a separation of the earthquake and explosion samples consistent enough to provide reliable discrimination. However, spectral analyses of the data over the frequency band from 0.5 to 5.0 Hz revealed significant differences in the spectra of certain regional phases which proved to be a quite reliable discriminant. In particular, both the Pg and Lg spectra from earthquakes have been found to be richer in high-frequency content than corresponding explosion spectra. A discriminant measure, defined as the ratio of average Lg spectral amplitude level in the 0.5- to 1.0-Hz passband to that in the 2.0- to 4.0-Hz passband, provides good separation of earthquake and explosion populations.

scholarly journals The May 7 - 11, 2016 Earthquake Sequence at Rivera Fault Zone

2020 ◽  
Author(s):  
Francisco J Nunez-Cornu ◽  
Diego Cordoba ◽  
William L Bandy ◽  
Juan José Dañobeitia ◽  
Carlos Mortera-Gutierrez ◽  
...  
Keyword(s):  
Pressure Sensors ◽  
Velocity Model ◽  
Tectonic Stress ◽  
Seismic Network ◽  
P Wave ◽  
Earthquake Sequence ◽  
Ocean Bottom ◽  
Transform Fault ◽  
Stress Regime ◽  
Short Period

<p>The geodynamic complexity in the interaction between Rivera, Cocos and NOAM plates is mainly reflected in the high and not well located seismicity of the region. In the framework of TsuJal Project, a study of the passive seismic activity was carried out. A temporal seismic network with 25 Obsidian stations with sensor Le-3D MkIII were deploying from the northern part of Nayarit state to the south of Colima state, including the Marias Islands, in addition to the Jalisco telemetric Seismic Network, being a total of 50 seismic stations on land. Offshore, ten Ocean Bottom Seismographs type LCHEAPO 2000 with 4 channels (3 seismic short period and 1 pressure sensors) were deployed and recover by the BO El Puma from UNAM in an array from the Marias Islands to off coast of the border of Colima and Michoacan state, in the period from 19th April to 7th November 2016.</p><p>A seismic sequence started on May 7, 2016 with an earthquake Mw = 5.6 reported by CMT-Harvard, USGS and SSN at the area north of Paleo Rivera Transform fault and west of the Middle America Trench, an area with a very complex tectonics due to the interaction of Rivera, Cocos and NOAM plates.</p><p>An analysis of this earthquake sequence from May 7 to May 11 using data from OBS and adequate P-Wave velocity model for Rivera plate is presented, 87 earthquakes were located. Data from onland stations were integrated after a travel-time residual analysis.</p><p>We observed that the new location is about 50 km southwest direction, from previous one, between the Paleo Rivera Transform fault and the northern tip of the East Pacific Rise – Pacific Cocos Segment.  This area has a different tectonic stress regime.</p>

scholarly journals A first look at the Gargano (southern Italy) seismicity as seen by the local scale OTRIONS seismic network

2014 ◽  
Vol 57 (4) ◽  
Author(s):  
Salvatore de Lorenzo ◽  
Annalisa Romeo ◽  
Luigi Falco ◽  
Maddalena Michele ◽  
Andrea Tallarico
Keyword(s):  
Southern Italy ◽  
Velocity Model ◽  
Local Scale ◽  
Seismic Network ◽  
P Wave ◽  
Travel Times ◽  
Velocity Models ◽  
P Wave Velocity ◽  
Short Period ◽  
Inversion Procedure

<p>On April 2013, a local scale seismic network, named OTRIONS, composed of twelve short period (1 Hz) three component seismometers, has been located in the northern part of the Apulia (southern Italy). In the first two months of data acquisition, the network recorded about one hundred very small (M<span><sub>L</sub></span>&lt;2) magnitude earthquakes. A three-layer 1D V<span><sub>P</sub></span> velocity model was preliminarily computed, using the recordings of earthquakes occurred in the area in the period 2006-2012 and recorded by the national seismic network of INGV (Istituto Nazionale di Geofisica e Vulcanologia). This model was calibrated by means of a multi-scale approach, based on a global search of the minimum misfit between observed and theoretical travel times. At each step of the inversion, a grid-search technique was implemented to infer the elastic properties of the layers, by using HYPO71 to compute the forward models. In a further step, we used P and S travel times of both INGV and OTRIONS events to infer a minimum 1D V<span><sub>P</sub></span> velocity model, using a classical linearized inversion approach. Owing to the relatively small number of data and poor coverage of the area, in the inversion procedure, the V<span><sub>P</sub></span>/V<span><sub>S</sub></span> ratio was fixed to 1.82, as inferred from a modified Wadati diagram. The final 1D velocity model was obtained by averaging the inversion results arising from nine different initial velocity models. The inferred V<span><sub>P</sub></span> velocity model shows a gradual increase of P wave velocity with increasing the depth. The model is well constrained by data until to a depth of about 25-30 km.</p>

EFFECT OF SEDIMENTARY THICKNESS ON SHORT‐PERIOD RAYLEIGH‐WAVE DISPERSION

Geophysics ◽  
1965 ◽  
Vol 30 (2) ◽  
pp. 198-203 ◽  
Author(s):  
T. V. McEvilly ◽  
William Stauder
Keyword(s):  
Rayleigh Waves ◽  
Wave Dispersion ◽  
Illinois Basin ◽  
Well Control ◽  
Short Period ◽  
Single Station ◽  
Basement Depth ◽  
Basin Area ◽  
Rayleigh Wave Dispersion ◽  
Group Velocities

Large differences in group velocities of short‐period Rayleigh waves from stripmine blasts for different propagation paths in the Ozark Uplift‐Illinois Basin area have been observed. Good well control in the area makes possible the construction of structural models of the sediments‐basement system for these paths. Theoretical group velocities computed for these models agree well with observations, thus explaining the large variations in velocities in terms of basement‐depth differences. This sensitivity of short‐period surface waves to sedimentary thickness suggests an inexpensive, single‐station technique of basin reconnaissance where commercial blasting is available.

Azimuthal anomalies of short-period P-wave arrivals from Nahanni aftershocks, Northwest Territories, Canada, and effects of surface topography

1990 ◽  
Vol 80 (5) ◽  
pp. 1272-1283
Author(s):  
Goetz G. R. Buchbinder ◽  
R. A. W. Haddon
Keyword(s):  
Surface Topography ◽  
Northwest Territories ◽  
P Wave ◽  
Digital Data ◽  
Aftershock Activity ◽  
P Waves ◽  
Short Period ◽  
Order Of Magnitude ◽  
Large Earthquakes ◽  
Theoretical Results

Abstract Following two large earthquakes in the Northwest Territories of Canada in 1985 and one in 1988, four field surveys were undertaken to study the extensive aftershock activity. Some of the seismographs employed recorded three-component digital data, which allowed the directions of approach of short-period P-wave arrivals to be analyzed. At three stations, observed azimuthal deviations reached as much as 40° from theoretically expected azimuths as computed from the inferred hypocenters for the events. Theoretical results are presented that support the hypothesis that the observed azimuthal deviations are caused principally by local topographic slopes in the vicinity of the recording instruments. Similar theoretical results indicate that effects of local surface topography on arrival azimuths of SH and SV waves are nearly an order of magnitude less than for P waves, so that such effects will generally be unimportant in shear wave splitting studies.

scholarly journals Shallow velocity model in the area of Pozzo Pitarrone, Mt. Etna, from single station, array methods and borehole data

2016 ◽  
Vol 59 (4) ◽  
Author(s):  
Luciano Zuccarello ◽  
Mario Paratore ◽  
Mario La Rocca ◽  
Ferruccio Ferrari ◽  
Alfio Messina ◽  
...  
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Seismic Noise ◽  
Velocity Model ◽  
P Wave ◽  
Borehole Data ◽  
P Wave Velocity ◽  
Single Station ◽  
Mt Etna

<p>Seismic noise recorded by a temporary array installed around Pozzo Pitarrone, NE flank of Mt. Etna, have been analysed with several techniques. Single station HVSR method and SPAC array method have been applied to stationary seismic noise to investigate the local shallow structure. The inversion of dispersion curves produced a shear wave velocity model of the area reliable down to depth of about 130 m. A comparison of such model with the stratigraphic information available for the investigated area shows a good qualitative agreement. Taking advantage of a borehole station installed at 130 m depth, we could estimate also the P-wave velocity by comparing the borehole recordings of local earthquakes with the same event recorded at surface. Further insight on the P-wave velocity in the upper 130 m layer comes from the surface reflected wave observable in some cases at the borehole station. From this analysis we obtained an average P-wave velocity of about 1.2 km/s, compatible with the shear wave velocity found from the analysis of seismic noise.</p>

TO STUDY THE EFFECT OF BMV ON P WAVE DISPERSION AND SHORT TERM PROGNOSTIC IMPACT OF P WAVE DISPERSION IN PREDICTION OF CLINICAL OUTCOME AFTER PERCUTANEOUS BALLOON MITRAL VALVULOPLASTY IN PATIENTS WITH MITRAL STENOSIS AND SINUS RHYTHM

2020 ◽  
Vol 4 (9) ◽  
Author(s):  
Ashish Kumar Agarwal ◽  
Daulat Singh Meena ◽  
Vijay Pathak ◽  
Anoop Jain ◽  
Rakesh Kumar Ola
Keyword(s):  
Clinical Outcome ◽  
Right Ventricular ◽  
Wave Dispersion ◽  
Tissue Doppler ◽  
P Wave ◽  
Short Term ◽  
P Wave Dispersion ◽  
Mitral Valvuloplasty ◽  
Percutaneous Balloon ◽  
Before And After

Background: The aim of the present study was to study the effect of percutaneous balloon mitral  valvuloplasty (PBMV) on P wave dispersion and to test the correlation between P-maximum and  P-dispersion to right ventricular function and pulmonary artery pressure before and after PMBV. Also to study the impact of P-maximum and P-wave dispersion on the short term clinical outcome after successful PBMV in patients with mitral stenosis (MS) and sinus rhythm. Methods: 75 patients undergoing PMBV were enrolled in this study. We evaluated P-maximum, P-minimum and P-wave dispersion before and one month and one year after PBMV . We studied the changes in pulmonary arterial pressure (PAP), left atrial (LA) dimension, mitral diastolic gradient, and mitral valve area, in addition to the changes in right ventricular function utilizing tissue Doppler assessment both before and after PMBV, in addition the role of the P-wave dispersion in prediction of late cardiac events. Results: There were significant decrease in mean diastolic gradient, PAP, and LA size and significant improvement in right ventricular tissue Doppler indices after PMBV. Accompany these hemodynamic changes after PMBV. P-maximum and P-wave dispersion were found to be decreased (P < 0.001). Conclusion: Successful PBMV was associated with a decrease in Pmax and PWD. These simple electrocardiographic indices may predict the success of the procedure immediately after PBMV.  The P-maximum and P-wave dispersion changes were correlated with significant impairment of right dysfunction and the degree of pulmonary artery pressure. Keywords: PBMV.PAP,LA

scholarly journals Evaluation of left atrial mechanics and p-wave dispersion as markers of left atrial cardiopathy in patients of embolic stroke of undetermined source (ESUS)

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
S Masood ◽  
M.M Azharuddin ◽  
S.M.K Ashraf ◽  
S Wahab
Keyword(s):  
Left Atrial ◽  
Wave Dispersion ◽  
Embolic Stroke ◽  
P Wave ◽  
Electromechanical Delay ◽  
P Wave Dispersion ◽  
Atrial Electromechanical Delay ◽  
Wave Duration ◽  
P Wave Duration ◽  
Increased Risk

Abstract Introduction Around 25% of all ischaemic strokes have no known cause despite standard investigations. Most of these cases are suspected to have an embolic source for ischaemia, leading to the moniker of Embolic Stroke of Undetermined Source (ESUS). Recent studies suggest that abnormalities of the left atrium, in the form of atrial cardiopathy, can lead to increased risk of stroke even in the absence of atrial fibrillation (AF), which may be either as precursors to AF or as independent risk factors for the development of left atrial thrombus and subsequent stroke. Purpose The aim of this study was to measure LA electromechanical dissociation, LA volumes and P-wave dispersion as markers of atrial cardiopathy in patients with ESUS to determine whether atrial cardiopathy may be in the causal pathway of ESUS. Methods 28 patients presenting with ischaemic stroke and fulfilling the criteria for ESUS were enrolled into this cross-sectional, observational study. All patients had 24-hour Holter monitoring done to rule out the presence of AF. The control group consisted of 28 age- and gender-matched apparently healthy individuals. On ECG, P-wave Dispersion (PWD) was calculated by subtracting minimum P-wave duration from maximum P-wave duration. On echocardiography, time intervals from the beginning of P-wave to beginning of A' wave from the lateral mitral annulus in tissue doppler imaging was measured as the atrial electromechanical delay. LA volumes were recorded using the Modified Biplane Simpson's method. Statistical analysis was performed using student's t-test, chi-square test, and Pearson's test. Results Baseline demographic and laboratory characteristics were similar between the two groups. Increased PWD (34.14±9.89 ms vs. 27.32±8.95 ms; p=0.01), atrial electromechanical delay (73.32±16.31 ms vs. 63.63±13.59 ms; p=0.02) and LA volumes were observed in patients with ESUS as compared to controls. A significant correlation was also found between these parameters (p&lt;0.01). Discussion According to the results of our study, PWD, atrial electromechanical delay and LA volumes may be novel predictors for ESUS. Atrial cardiopathy is a unique mechanism of thrombo-embolism in ESUS patients and our data establishes its association with ESUS. Further studies will be needed to shed more light on its role in the causality of stroke in the ESUS population. Measurement of electromechanical delay Funding Acknowledgement Type of funding source: None

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