High-frequency spectral scaling of a main shock/ aftershock sequence near the Norwegian coast

1988 ◽  
Vol 78 (2) ◽  
pp. 561-570
Author(s):  
Eric P. Chael ◽  
Richard P. Kromer
Keyword(s):  
Stress Drop ◽  
High Frequency ◽  
Background Noise ◽  
Main Shock ◽  
Source Model ◽  
Aftershock Sequence ◽  
Constant Stress ◽  
P Wave ◽  
Western Coast ◽  
Seismic Signals

Abstract A high-frequency seismic element was recently added to the NORESS regional array in Norway. This system can monitor seismic signals at frequencies up to 50 Hz. In February 1986, the high-frequency seismic element recorded an mbLg 4.7 main shock and several aftershocks which occurred 420 km northwest of NORESS, off Norway's western coast. These events produced high-frequency signals which were well above the background noise at the station. P-wave spectra of these events scale in a manner consistent with the ω-square, constant-stress-drop source model. The data do not require any change in this scaling to magnitudes (mbLg) below 2, in contrast to previous reports that constant-stress-drop scaling breaks down at smaller magnitudes.

A fault model for the Nahanni earthquakes from aftershock studies

1990 ◽  
Vol 80 (6A) ◽  
pp. 1553-1570 ◽  
Author(s):  
R. B. Horner ◽  
R. J. Wetmiller ◽  
M. Lamontagne ◽  
M. Plouffe
Keyword(s):  
Stress Drop ◽  
Main Shock ◽  
Fault Zones ◽  
Aftershock Sequence ◽  
Aftershock Activity ◽  
Thrust Faulting ◽  
Rupture Plane ◽  
To Come ◽  
Activity Mechanism ◽  
Secondary Fault

Abstract Relative locations of 323 large aftershocks (M 3.0 or greater) in the period from 5 October 1985 to 25 March 1988 show that the Ms 6.6 event on 5 October 1985 initiated at 62.208°N, 124.217°W, about 2.5 km northeast of the Ms 6.9 main shock on 23 December 1985. The overall aftershock distribution suggests the October rupture was primarily a west-dipping, low-angle thrust. In subsequent aftershock activity, the main rupture plane was marked by a distinct quiescent area of about 200 km2 that persisted until the 23 December event. Most of the stress drop and slip occurred in this area. Following the 23 December rupture, a similar sized quiescent zone was also observed; however, it was only evident during the first 24 hr of the aftershock sequence, and the area was about 50 per cent too small to yield the overall stress drop. The additional area appeared to come from secondary rupture zones that developed coincident with the main shock rupture. Precise locations of 182 small (M 3.0 or less) aftershocks recorded during a third field survey from 12 to 21 September 1986 indicated at least one and probably three high-angle faults. Composite mechanism solutions showed thrust faulting except in a region directly south of the main shock rupture areas where there is a bend in one of the secondary fault zones and a concentration of aftershock activity. Mechanism solutions calculated for five of the largest aftershocks in the same region also indicated a similar variability. Development of secondary fault zones explained the increased complexity of the December event and may also provide an explanation for the vertical peak acceleration exceeding 2 g that was recorded about 10 sec after the December rupture initiated.

Source parameter analysis from strong motion records of the Friuli, Italy, earthquake sequence (1976-1977)

1987 ◽  
Vol 77 (4) ◽  
pp. 1127-1146
Author(s):  
Giuseppe De Natale ◽  
Raul Madariaga ◽  
Roberto Scarpa ◽  
Aldo Zollo
Keyword(s):  
Frequency Domain ◽  
Stress Drop ◽  
High Frequency ◽  
Epicentral Distance ◽  
Strong Motion ◽  
Source Model ◽  
Parameter Analysis ◽  
Corner Frequency ◽  
Spectral Parameters ◽  
Single Station

Abstract Time and frequency domain analyses are applied to strong motion data recorded in Friuli, Italy, during 1976 to 1977. An inversion procedure to estimate spectral parameters (low frequency level, corner frequency, and high frequency decay) has been applied to displacement spectra using a simple earthquake source model with a single corner frequency. The data were digitized accelerograms from ENEA-ENEL portable and permanent networks. Instrument-corrected SH waves were selected from a set of 138 three-component, hand-digitized records and 28 automatically digitized records. Thirty-eight events with stations having 8 to 32 km epicentral distance were studied. Different stress drop estimates were performed showing high values (200 to 300 bars, on the average) with seismic moments ranging from 2.8 × 1022 to 8.0 × 1024 dyne-cm. The observation of systematic higher values of Brune stress drop (obtained from corner frequencies) with respect to other time and frequency domain estimates of stress release, and the evidence on time series of multiple rupture episodes suggest that the observed corner frequencies are most probably related to subevent ruptures rather than the overall fault size. Seven events recorded at more than one station show a good correlation between rms, Brune, and dynamic stress drops, and a constant scaling of this parameter as a function of the seismic moment. When single station events are also considered, a slight moment dependence of these three stress drop estimates is observed differently. This may be explained by an inadequacy of the ω−2 high-frequency decay of the source model or by high-frequency attenuation due to propagation effects. The high-frequency cutoff of acceleration spectra indicates the presence of an Fmax in the range of 5 to 14 Hz, except for the stations where local site effects produce spectral peaks.

Source dynamics of the Dasht-e Bayāz earthquake of August 31, 1968

1969 ◽  
Vol 59 (5) ◽  
pp. 1843-1861
Author(s):  
Mansour Niazi
Keyword(s):  
Stress Drop ◽  
Main Shock ◽  
Mean Value ◽  
The Body ◽  
P Wave ◽  
Polarization Angle ◽  
S Wave ◽  
Long Duration ◽  
First Motion ◽  
Complicated Pattern

abstract Radiation patterns of the P-wave first motion and S-wave polarization angle of the Dasht-e Bayāz earthquake of August 31, 1968, as well as its principal aftershock which occurred about 20 hours after the main shock are studied. The main shock data are consistent with the observed left-lateral strike-slip fault which accompanied it. The radiation pattern of the aftershock differs somewhat from that of the main shock and agrees with the directions of the secondary faulting in the area. Several lines of evidence pointing to a multiple source for the main shock are presented. They include complexity of the body phases, low value of the rupture speed as studied from the analysis of the surface wave spectra, reported long duration of shaking and complicated pattern of striations produced by faulting. Energy, moment and stress drop associated with the main shock are estimated. The resulting mean value of stress drop over the faulted surface has a range of 40-100 bars. Based on the age of some well-built structures in the area, it is proposed that no earthquake as severe as the recent one has occurred near the location of the August 31, 1968 earthquake during the last 800 years.

Estimating plume heights of explosive eruptions using high-frequency seismic amplitudes

2019 ◽  
Vol 219 (2) ◽  
pp. 1365-1376 ◽  
Author(s):  
Azusa Mori ◽  
Hiroyuki Kumagai
Keyword(s):  
High Frequency ◽  
Seismic Source ◽  
Source Model ◽  
Explosive Eruptions ◽  
Seismic Signals ◽  
Volume Flux ◽  
Plinian Eruptions ◽  
Seismic Waveform ◽  
Eruption Volume ◽  
Seismic Amplitudes

SUMMARY Seismic signals during explosive eruptions have been correlated to eruption size or eruption volume flux for individual eruptive episodes. However, the universality of these correlations has yet to be confirmed. We quantified the sources of high-frequency seismic signals associated with sub-Plinian and Vulcanian eruptions at Kirishima (Japan), Tungurahua (Ecuador) and other volcanoes in Japan using a simple approach based on highly scattered seismic waveform characteristics. We found that eruption plume heights scale to seismic source amplitudes and are described by two relations depending on the value of source amplitudes: power-law and exponential relations for plume height >6 km and <6 km, respectively. Though conceptually similar, our scaling relations differ from the previously proposed relation based on reduced displacement. By comparing seismic and geodetic data during sub-Plinian eruptions at Kirishima, we found that the source amplitude is proportional to eruption volume flux. Combining these relations, we show that our scaling relation for Plinian eruptions is consistent with predictions from plume dynamics models. We present a source model to explain the proportionality between the source amplitude and eruption volume flux assuming a vertical crack or a cylindrical conduit as the source. The source amplitude can be estimated in seconds without any complicated data processing, whereas eruption plumes take minutes to reach their maximum heights. Our results suggest that high-frequency seismic source amplitudes are useful for estimating plume heights in real time.

Far-field pulse shapes from circular sources with variable rupture velocities

1997 ◽  
Vol 87 (5) ◽  
pp. 1288-1296
Author(s):  
Nicholas Deichmann
Keyword(s):  
Stress Drop ◽  
Seismic Moment ◽  
Total Duration ◽  
Source Model ◽  
P Wave ◽  
Far Field ◽  
Rupture Velocity ◽  
P Waves ◽  
S Waves ◽  
Rate Functions

Abstract Recently, Sato (1994) developed a simple earthquake source model of a circular rupture expanding outward from the center of a fault with constant stress drop. In contrast to previous models, the rupture velocity is allowed to vary over the duration of faulting. This model is used to synthesize apparent moment-rate functions for a three-stage source process: first, the rupture starts out with a gradually increasing velocity, then, it continues to expand uniformly until, finally, it slows to a gradual stop. Synthetic velocity seismograms are obtained from a convolution of the apparent moment-rate functions with a causal Q-operator and an appropriate instrument response. Comparisons with an example of an earthquake signal show that, in the context of the proposed model, the observed emergent P-wave onset, which is not compatible with a constant rupture velocity, can be explained by a gradually accelerating rupture front. Systematic departures from the generally expected scaling relationship between seismic moment and rupture duration are often interpreted as evidence for a dependence of stress drop on seismic moment. However, the trade-off between stress drop and rupture velocity inherent in all kinematic source models implies that such deviations can just as well be attributed to systematic variations of rupture velocity. Whereas, in general, the total duration of the far-field displacement pulse is shorter for P waves than for S waves, the model predicts that the rise time, τ1/2, of the displacement pulse should be longer for P waves than for S waves. This feature could constitute a critical test of the model and also provide a constraint on the rupture velocity.

Seismic Magnitudes, Corner Frequencies, and Microseismicity: Using Ambient Noise to Correct for High-Frequency Attenuation

2020 ◽  
Vol 110 (3) ◽  
pp. 1260-1275 ◽  
Author(s):  
Antony Butcher ◽  
Richard Luckett ◽  
J.-Michael Kendall ◽  
Brian Baptie
Keyword(s):  
Stress Drop ◽  
High Frequency ◽  
Seismic Noise ◽  
Seismic Risk ◽  
Ambient Noise ◽  
Source Model ◽  
Lower Stress ◽  
Microseismic Activity ◽  
Stress Drops ◽  
Seismic Catalog

ABSTRACT Over recent years, a greater importance has been attached to low-magnitude events, with increasing use of the subsurface for industrial activities such as hydraulic fracturing and enhanced geothermal schemes. Magnitude distributions and earthquake source properties are critical inputs when managing the associated seismic risk of these activities, yet inconsistencies and discrepancies are commonly observed with microseismic activity (M&lt;2). This, in part, is due to their impulse response being controlled by the medium, as opposed to the source. Here, an approach for estimating the high-frequency amplitude decay parameter from the spectral decay of ambient seismic noise (κ0_noise) is developed. The estimate does not require a pre-existing seismic catalog and is independent of the source properties, so avoids some of the main limitations of earthquake-based methods. We then incorporate κ0_noise into the Brune (1970) source model and calculate source properties and magnitude relationships for coal-mining-related microseismic events, recorded near New Ollerton, United Kingdom. This generates rupture radii ranging approximately between 10 and 100 m, which agrees with the findings of Verdon et al. (2018), and results in stress-drop values between 0.1 and 10 MPa. Calculating these properties without κ0_noise produces much higher rupture radii of between 100 and 500 m and significantly lower stress drops (∼1×10−2  MPa). Finally, we find that the combined κ0-Brune model parameterized with these source property estimates accurately capture the ML–Mw relationship at New Ollerton, and that stress drop heavily influences the gradient of this relationship.

scholarly journals Stress-Drop and Source Scaling of the 2019 Ridgecrest, California, Earthquake Sequence

2020 ◽  
Vol 110 (4) ◽  
pp. 1859-1871 ◽  
Author(s):  
Daniel T. Trugman
Keyword(s):  
Stress Drop ◽  
Aftershock Sequence ◽  
P Wave ◽  
Earthquake Sequence ◽  
Study Region ◽  
Decomposition Approach ◽  
Trade Offs ◽  
Stress Changes ◽  
Source Scaling ◽  
Stress Drops

ABSTRACT Stress drop, while difficult to measure reliably and at scale, is a key source parameter for understanding the earthquake rupture process and its relationship to strong ground motion. Here, we use a P-wave spectral decomposition approach, designed for large and densely sampled datasets, to measure earthquake stress drop in the region surrounding the 2019 Ridgecrest, California, earthquake sequence. With more than 11,000 measurements of earthquake stress drop in the 20-yr time period from 2000 through 2019, this dataset provides an opportunity to understand how coseismic stress changes and how other geophysical factors relate to the distribution of stress drop and its evolution in space and time. We observe a mild but persistent deviation from self-similar scaling, with larger events having systematically higher stress drops, though this trend depends on the assumption of an omega-square source spectral model. Earthquake stress drop increases with hypocentral depth in this study region, and the Ridgecrest aftershocks tend to have higher stress drops than the pre-event seismicity. This is in part due to their deeper hypocenters. Coherent spatial patterns of stress drop in the aftershock sequence correlate with the slip distribution of the M 7.1 mainshock, whose northwest rupture tip terminated in a long-lived zone of enervated stress drop. Although physical interpretation of these results is complicated by the trade-offs between the timing, depth, and location of these earthquakes, the observations provide new insight into the physics of the earthquake source in an area of renewed seismic activity in southern California.

scholarly journals Determination of rupture duration and stress drop for earthquakes in southern California

1983 ◽  
Vol 73 (6A) ◽  
pp. 1527-1551
Author(s):  
Arthur Frankel ◽  
Hiroo Kanamori
Keyword(s):  
Stress Drop ◽  
Pulse Width ◽  
Southern California ◽  
Main Shock ◽  
P Wave ◽  
Fault System ◽  
Zero Crossing ◽  
Main Shocks ◽  
Seismic Networks ◽  
Rupture Duration

Abstract A simple technique is developed for determining the rupture duration and stress drop of earthquakes between magnitudes 3.5 and 4.0 using the time between the P-wave onset and the first zero crossing (τ1/2) on seismograms from local seismic networks. This method is applied to 10 main shocks in southern California to investigate regional variations in stress drop. The initial pulse widths of 65 foreshocks or aftershocks of these events were measured. Values of τ1/2 for small earthquakes below about magnitude 2.2 are generally observed to remain constant with decreasing magnitude in four sequences studied. The relative pulse width of a particular main shock (M ≧ 3.5) at a given station is found to be correlated with the relative pulse width of its aftershocks recorded at that station. These observations are interpreted to signify that the waveforms of these small events (M ≦ 2.2) are essentially the impulse response of the path between the source and receiver. Values of τ1/2 determined from small foreshocks and aftershocks are, therefore, subtracted (in effect deconvolved) from those of each main shock to obtain an estimate of the rupture duration of the main shock which is corrected for path effects. Significant variations in rupture duration and stress drop are observed for the main shocks studied. Aftershock locations and azimuthal variations in τ1/2 both indicate that the rupture zone of one earthquake expanded unilaterally. A factor of 10 variation in stress drop is calculated for two adjacent events of similar seismic moments occurring 1 hr apart on the San Jacinto fault system. The first event in this pair had the highest stress drop of the events studied (860 bars) and was followed within 8 months by a magnitude 5.5 earthquake 2 km away.

Seismicity and waveforms of the microearthquakes before and after the Shizuoka-Seibu earthquake, central Japan

1984 ◽  
Vol 74 (2) ◽  
pp. 605-620
Author(s):  
Mizuho Ishida ◽  
Masakazu Ohtake
Keyword(s):  
High Frequency ◽  
Main Shock ◽  
Amplitude Ratio ◽  
High Stress ◽  
Aftershock Sequence ◽  
Central Japan ◽  
Before And After ◽  
Asperity Model ◽  
Source Dimension ◽  
Large Earthquakes

Abstract Investigating the foreshock-main shock-aftershock sequence of the Shizuoka-Seibu earthquake (M = 2.8, 16 January 1981), central Japan, we found evidence that suggests high stress conditions for the foreshock period. The source dimension of the main shock was roughly estimated to be about 0.5 × 0.2 km2. The m value of the Ishimoto-lida's formula was 1.87 for foreshocks and 2.37 for aftershocks. Waveforms of the foreshocks, main shock, and aftershocks were similar to each other. However, the amplitude ratio of the low (0.9 to 0.8 Hz) to high (3.5 to 10 Hz) frequency band was different between the foreshocks and aftershocks. The ratio for the foreshocks was lower than that for the aftershocks, indicating that the foreshocks contain more high-frequency energy than the aftershocks. The Shizuoka-Seibu sequence included a larger number of foreshocks (70) compared to aftershocks (43). This characteristic, in contrast with large earthquakes, was found common to small-sized earthquakes occurring in the neighborhood areas. These observations can be interpreted based on the asperity model.

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