Seismicity rate change before the Irpinia (M = 6.9) 1980 earthquake

1997 ◽  
Vol 87 (2) ◽  
pp. 318-326 ◽  
Author(s):  
M. Wyss ◽  
R. Console ◽  
M. Murru
Keyword(s):  
Southern Italy ◽  
Seismic Quiescence ◽  
Magnitude Scale ◽  
Data Sets ◽  
Data Set ◽  
Background Rate ◽  
Seismicity Rate ◽  
Rupture Area ◽  
The Stability ◽  
Precursory Seismic Quiescence

Abstract The stability of seismicity rate in central and southern Italy was examined in two data sets: from 1975.0 to 1995.0 with M ≧ 3.4 and from 1987.5 to 1996.0 with M ≧ 2.5. These are the approximate minimum magnitudes of complete reporting for the respective periods. The first set was used to evaluate the possibility that the 23 November 1980 Irpinia (M 6.9) earthquake was preceded by precursory seismic quiescence; the second was used to evaluate the conditions under which a current seismic quiescence could be detected in central or southern Italy. During the years before the Irpinia earthquake, the seismicity rate in the northern half of the rupture area and north of it was low. Whether this was a case of precursory quiescence or not is subject to interpretation because the background rate cannot be established for the years before 1975. If we accept the relatively constant seismicity rate in the Irpinia volume during the decade after the mainshock as representative for the background rate, we have a clear case of precursory quiescence lasting at least 1.3 yr up to the mainshock. Alternatively, it can be postulated that the seismicity rate during the decade following this shock was elevated regionally because of the stress redistribution and that the low rates seen before it represent the normal background rate. Even if this reasoning is accepted, the fact remains that a volume including the northern part of the rupture produced no M ≧ 3.4 earthquakes during 1.3 yr before the Irpinia earthquake but produced 10 earthquakes during the 4.7 previous yr. Given these facts, we favor the interpretation that the Irpinia 1980 earthquake was preceded by precursory seismic quiescence. In the entire data set, there are three other cases of quiescence of higher significance without a mainshock following. Since no other mainshock with M > 6 exists in the data set, no missed event exists. We propose that in Italy precursory seismic quiescence may precede mainshocks and that it may be detected in the future by the improved catalog of the modern data set beginning in 1987.5. Major magnitude scale changes give the mistaken appearance that fewer large-magnitude earthquakes occur in Italy now than in years before 1987. We postulate that the rate of earthquakes has not changed and that the magnitude scale should be adjusted.

Seismic quiescence, stress drops, and asperities in the New Hebrides arc

1983 ◽  
Vol 73 (1) ◽  
pp. 219-236
Author(s):  
M. Wyss ◽  
R. E. Habermann ◽  
Ch. Heiniger
Keyword(s):  
High Stress ◽  
Plate Boundary ◽  
Seismic Quiescence ◽  
Data Set ◽  
Seismicity Rate ◽  
Seismic Gaps ◽  
Main Shocks ◽  
Seismicity Rates ◽  
New Hebrides ◽  
Stress Drops

abstract The rate of occurrence of earthquakes shallower than 100 km during the years 1963 to 1980 was studied as a function of time and space along the New Hebrides island arc. Systematic examination of the seismicity rates for different magnitude bands showed that events with mb < 4.8 were not reported consistently over time. The seismicity rate as defined by mb ≧ 4.8 events was examined quantitatively and systematically in the source volumes of three recent main shocks and within two seismic gaps. A clear case of seismic quiescence could be shown to have existed before one of the large main shocks if a major asperity was excluded from the volume studied. The 1980 Ms = 8 rupture in the northern New Hebrides was preceded by a pattern of 9 to 12 yr of quiescence followed by 5 yr of normal rate. This pattern does not conform to the hypothesis that quiescence lasts up to the mainshock which it precedes. The 1980 rupture also did not fully conform to the gap hypothesis: half of its aftershock area covered part of a great rupture which occurred in 1966. A major asperity seemed to play a critical role in the 1966 and 1980 great ruptures: it stopped the 1966 rupture, and both parts of the 1980 double rupture initiated from it. In addition, this major asperity made itself known by a seismicity rate and stress drops higher than in the surrounding areas. Stress drops of 272 earthquakes were estimated by the MS/mb method. Time dependence of stress drops could not be studied because of changes in the world data set of Ms and mb values. Areas of high stress drops did not correlate in general with areas of high seismicity rate. Instead, outstandingly high average stress drops were observed in two plate boundary segments with average seismicity rate where ocean floor ridges are being subducted. The seismic gaps of the central and northern New Hebrides each contain seismically quiet regions. In the central New Hebrides, the 50 to 100 km of the plate boundary near 18.5°S showed an extremely low seismicity rate during the entire observation period. Low seismicity could be a permanent property of this location. In the northern New Hebrides gap, seismic quiescence started in mid-1972, except in a central volume where high stress drops are observed. This volume is interpreted as an asperity, and the quiescence may be interpreted as part of the preparation process to a future large main shock near 13.5°S.

Sparse reflectivity inversion for nonstationary seismic data with surface-related multiples: Numerical and field-data experiments

Geophysics ◽  
2017 ◽  
Vol 82 (3) ◽  
pp. R199-R217 ◽  
Author(s):  
Xintao Chai ◽  
Shangxu Wang ◽  
Genyang Tang
Keyword(s):  
Seismic Data ◽  
Resolution Enhancement ◽  
Synthetic Data ◽  
Data Sets ◽  
Data Set ◽  
Anelastic Attenuation ◽  
Seismic Resolution ◽  
Text Filtering ◽  
The Stability ◽  
Reflectivity Inversion

Seismic data are nonstationary due to subsurface anelastic attenuation and dispersion effects. These effects, also referred to as the earth’s [Formula: see text]-filtering effects, can diminish seismic resolution. We previously developed a method of nonstationary sparse reflectivity inversion (NSRI) for resolution enhancement, which avoids the intrinsic instability associated with inverse [Formula: see text] filtering and generates superior [Formula: see text] compensation results. Applying NSRI to data sets that contain multiples (addressing surface-related multiples only) requires a demultiple preprocessing step because NSRI cannot distinguish primaries from multiples and will treat them as interference convolved with incorrect [Formula: see text] values. However, multiples contain information about subsurface properties. To use information carried by multiples, with the feedback model and NSRI theory, we adapt NSRI to the context of nonstationary seismic data with surface-related multiples. Consequently, not only are the benefits of NSRI (e.g., circumventing the intrinsic instability associated with inverse [Formula: see text] filtering) extended, but also multiples are considered. Our method is limited to be a 1D implementation. Theoretical and numerical analyses verify that given a wavelet, the input [Formula: see text] values primarily affect the inverted reflectivities and exert little effect on the estimated multiples; i.e., multiple estimation need not consider [Formula: see text] filtering effects explicitly. However, there are benefits for NSRI considering multiples. The periodicity and amplitude of the multiples imply the position of the reflectivities and amplitude of the wavelet. Multiples assist in overcoming scaling and shifting ambiguities of conventional problems in which multiples are not considered. Experiments using a 1D algorithm on a synthetic data set, the publicly available Pluto 1.5 data set, and a marine data set support the aforementioned findings and reveal the stability, capabilities, and limitations of the proposed method.

scholarly journals Quantifying instrument errors in macromolecular X-ray data sets

2010 ◽  
Vol 66 (6) ◽  
pp. 733-740 ◽  
Author(s):  
Kay Diederichs
Keyword(s):  
Data Reduction ◽  
Spindle Speed ◽  
Experimental Setup ◽  
Data Sets ◽  
Signal To Noise ◽  
Instrument Error ◽  
Acta Cryst ◽  
Data Set ◽  
X Ray ◽  
The Stability

An indicator which is calculated after the data reduction of a test data set may be used to estimate the (systematic) instrument error at a macromolecular X-ray source. The numerical value of the indicator is the highest signal-to-noise [I/σ(I)] value that the experimental setup can produce and its reciprocal is related to the lower limit of the mergingRfactor. In the context of this study, the stability of the experimental setup is influenced and characterized by the properties of the X-ray beam, shutter, goniometer, cryostream and detector, and also by the exposure time and spindle speed. Typical values of the indicator are given for data sets from the JCSG archive. Some sources of error are explored with the help of test calculations usingSIM_MX[Diederichs (2009),Acta Cryst.D65, 535–542]. One conclusion is that the accuracy of data at low resolution is usually limited by the experimental setup rather than by the crystal. It is also shown that the influence of vibrations and fluctuations may be mitigated by a reduction in spindle speed accompanied by stronger attenuation.

scholarly journals How long do satellites need to overlap? Evaluation of climate data stability from overlapping satellite records

2017 ◽  
Vol 17 (24) ◽  
pp. 15069-15093 ◽  
Author(s):  
Elizabeth C. Weatherhead ◽  
Jerald Harder ◽  
Eduardo A. Araujo-Pradere ◽  
Greg Bodeker ◽  
Jason M. English ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Spectral Irradiance ◽  
Data Sets ◽  
Climate Data ◽  
Data Set ◽  
Long Term Stability ◽  
Earth Observations ◽  
Earth’S Climate ◽  
The Stability

Abstract. Sensors on satellites provide unprecedented understanding of the Earth's climate system by measuring incoming solar radiation, as well as both passive and active observations of the entire Earth with outstanding spatial and temporal coverage. A common challenge with satellite observations is to quantify their ability to provide well-calibrated, long-term, stable records of the parameters they measure. Ground-based intercomparisons offer some insight, while reference observations and internal calibrations give further assistance for understanding long-term stability. A valuable tool for evaluating and developing long-term records from satellites is the examination of data from overlapping satellite missions. This paper addresses how the length of overlap affects the ability to identify an offset or a drift in the overlap of data between two sensors. Ozone and temperature data sets are used as examples showing that overlap data can differ by latitude and can change over time. New results are presented for the general case of sensor overlap by using Solar Radiation and Climate Experiment (SORCE) Spectral Irradiance Monitor (SIM) and Solar Stellar Irradiance Comparison Experiment (SOLSTICE) solar irradiance data as an example. To achieve a 1 % uncertainty in estimating the offset for these two instruments' measurement of the Mg II core (280 nm) requires approximately 5 months of overlap. For relative drift to be identified within 0.1 % yr−1 uncertainty (0.00008 W m−2 nm−1 yr−1), the overlap for these two satellites would need to be 2.5 years. Additional overlap of satellite measurements is needed if, as is the case for solar monitoring, unexpected jumps occur adding uncertainty to both offsets and drifts; the additional length of time needed to account for a single jump in the overlap data may be as large as 50 % of the original overlap period in order to achieve the same desired confidence in the stability of the merged data set. Results presented here are directly applicable to satellite Earth observations. Approaches for Earth observations offer additional challenges due to the complexity of the observations, but Earth observations may also benefit from ancillary observations taken from ground-based and in situ sources. Difficult choices need to be made when monitoring approaches are considered; we outline some attempts at optimizing networks based on economic principles. The careful evaluation of monitoring overlap is important to the appropriate application of observational resources and to the usefulness of current and future observations.

scholarly journals Assessment of Odin-OSIRIS ozone measurements from 2001 to the present using MLS, GOMOS, and ozone sondes

2013 ◽  
Vol 6 (2) ◽  
pp. 3819-3857 ◽  
Author(s):  
C. Adams ◽  
A. E. Bourassa ◽  
V. Sofieva ◽  
L. Froidevaux ◽  
C. A. McLinden ◽  
...  
Keyword(s):  
Infrared Imaging ◽  
Imaging System ◽  
Data Sets ◽  
Validation Data ◽  
Data Set ◽  
Long Term Stability ◽  
Ozone Data ◽  
High Bias ◽  
The Stability

Abstract. The Optical Spectrograph and InfraRed Imaging System (OSIRIS) was launched aboard the Odin satellite in 2001 and is continuing to take limb-scattered sunlight measurements of the atmosphere. This work aims to characterize and assess the stability of the OSIRIS 11 yr v5.0x ozone data set. Three validation data sets were used: the v2.2 Microwave Limb Sounder (MLS) and v6 Global Ozone Monitoring of Occultation on Stars (GOMOS) satellite data records, and ozone sonde measurements. Global mean percent differences between coincident OSIRIS and validation measurements are within 5% of zero at all altitude layers above 18.5 km for MLS, above 21.5 km for GOMOS, and above 17.5 km for ozone sondes. Below 17.5 km, OSIRIS measurements agree with ozone sondes within 5% and are well-correlated (R > 0.75) with them. For low OSIRIS optics temperatures (< 16 °C), OSIRIS ozone measurements are biased low by up 6% compared with the validation data sets for 25.5–40.5 km. Biases between OSIRIS ascending and descending node measurements were investigated and were found to be related to aerosol retrievals below 27.5 km. Above 30 km, agreement between OSIRIS and the validation data sets was related to the OSIRIS retrieved albedo, which measures apparent upwelling, with a high bias for in OSIRIS data with large albedos. In order to assess the long-term stability of OSIRIS measurements, global average drifts relative to the validation data sets were calculated and were found to be < 3% per decade for comparisons against MLS for 19.5–36.5 km, GOMOS for 18.5–54.5 km, and ozone sondes for 12.5–22.5 km, and within error of 3% per decade at most altitudes. Above 36.5 km, the relative drift for OSIRIS versus MLS ranged from ~ 0–6%, depending on the data set used to convert MLS data to the OSIRIS altitude versus number density grid. Overall, this work demonstrates that the OSIRIS 11 yr ozone data set from 2001 to the present is suitable for trend studies.

scholarly journals Significance test for seismicity rate changes before the 1987 Chiba-toho-oki earthquake (M 6.7) Japan

1999 ◽  
Vol 42 (5) ◽  
Author(s):  
K. Maeda ◽  
S. Wiemer
Keyword(s):  
Quantitative Analysis ◽  
Real Time ◽  
Rate Increase ◽  
Significance Test ◽  
Seismic Quiescence ◽  
Rupture Zone ◽  
Seismicity Rate ◽  
Seismicity Rates ◽  
Seismicity Rate Changes ◽  
Precursory Seismic Quiescence

A precursory seismic quiescence lasting 1.5 ± 0.5 years was observed prior to the 1987 M 6.7 Chiba-toho-oki earthquake, Central Japan. This event was the largest mainshock to occur in the region in 60 years. A quantitative analysis of the seismicity rates, using two independent catalogs provided by the NIED and JMA networks, shows that the precursory seismic quiescence is centered in the shallower part of the rupture zone of the subsequent mainshock, at a depth of 20-40 km. At the hypocenter of the 1987 Chiba-toho-oki mainshock, a 50% increase in the seismicity rate was detected in the NIED data, coinciding in time with the onset of quiescence (1986.4 ± 0.5). The simultaneous appearance of both quiescence in the shallow part of the rupture zone observed in two catalogs, and a rate increase in the immediate hypocenter region, suggest that these phenomena are causally linked to the subsequent mainshock. However, a quantitative analysis of both catalogs reveals that the precursory quiescence and rate increase are not unique, since rate changes of this duration and significance often occur in the data. A rate change of this significance rating could probably not be detected as a precursor in a real time approach. For the aid of real time monitoring of seismicity rate changes, we introduce the method to calculate the 95-percentile of confidence level for the significant rate changes.

scholarly journals Quantitative mapping of precursory seismic quiescence before the 1989, M 7.1off-Sanriku earthquake, Japan

1999 ◽  
Vol 42 (5) ◽  
Author(s):  
M. Wyss ◽  
A. Hasegawa ◽  
S. Wiemer ◽  
N. Umino
Keyword(s):  
Main Shock ◽  
Time Window ◽  
Statistical Significance ◽  
Seismic Quiescence ◽  
Time And Space ◽  
Data Set ◽  
Rate Decrease ◽  
Aftershock Area ◽  
One Year ◽  
Precursory Seismic Quiescence

The first main shock of the off-Sanriku earthquake sequence (02/11/89, M 7.1; 18/07/92, M 6.9; 28/12/94, M 7.5) was preceded by a precursory seismic quiescence lasting 2.5 ± 1 year and up to this main shock. The detailed properties of this quiescence were mapped as a function of time and space by a gridding technique using the ZMAP computer code, and the statistical significance was estimated by generating a synthetic catalog based on the microearthquake catalog of Tohoku University, which was the data set used. The statistically most significant expression of this precursory quiescence has a probability of 0.1% to have occurred at random and was located in the eastern part of the 1989 aftershock area, at a point to which the 1994 aftershocks extended also. If we define the dimensions of the quiescence anomaly by a vertical cylinder with the depth of the entire seismogenic layer, centered at the point of most significant quiescence and showing a rate decrease of 75%, then we find its radius is 25 ± 9 km. If we allow other shapes, such as the simplified aftershock volume of 1989, or other simple geometric figures, to define the rate decrease we find dimensions of 80 by 80 km. The characteristics of the quiescence anomaly do not depend strongly on the choice of free parameters within the following ranges: 100 ? number of events ? 400, 2.0 ? Mmin £ 3.0, 1 ? time window ? 3 years. With our method, a thorough analysis of the period before the 1994 main shock is not possible because of the interference of the extended aftershock sequence of 1989. Nevertheless, we identified a quiescence of nearly zero earthquakes located near the center of the 1994 aftershock area that lasted for one year up to that main shock. However, this quiescence period ranked only 46th in significance, behind other quiescences of equal duration and similar dimensions distributed in time and space through the data set. Because of the ubiquitous existence of periods of near zero activity during short periods like one year, we find that quiescences shorter than about 1.5 years cannot be defined with high statistical significance in most earthquake catalogs. In the last two years of the data (1995.3-1997.3) we see no extensive quiescence of high significance off the east coast of Honshu between 36.5° and 42°N in the currently available data.

An Investigation of the Convergence of Average Peak Accelerations for High-Speed Planing Craft

2021 ◽  
Author(s):  
Michael R. Riley ◽  
Heidi P. Murphy ◽  
Brock W. Aron
Keyword(s):  
High Speed ◽  
Cumulative Distribution ◽  
Data Sets ◽  
Peak Acceleration ◽  
Multiple Sources ◽  
Data Set ◽  
Distribution Shape ◽  
Acceleration Data ◽  
Rough Water ◽  
The Stability

This paper summarizes the results of an investigation of the convergence of average peak accelerations as more and more peaks are recorded during rough-water trials of small high-speed craft. Existing guidance from multiple sources suggest that more peaks is better, but how much more, and what engineering rationale should substantiate the answer? To address the question, simplified equations and numerous examples of peak acceleration data sets are presented. The results demonstrate that convergence of the average of the highest 10 percent of peaks (A1/10), and the average of the highest 1 percent of peaks (A1/100), and the ratio means that the shape of the cumulative distribution of the data set becomes more stable as the number of peak acceleration data points increases. A simple percent difference criterion is presented for quantifying the stability of the cumulative distribution shape.

scholarly journals Relative drifts and stability of satellite and ground-based stratospheric ozone profiles at NDACC lidar stations

2012 ◽  
Vol 5 (6) ◽  
pp. 1301-1318 ◽  
Author(s):  
P. J. Nair ◽  
S. Godin-Beekmann ◽  
L. Froidevaux ◽  
L. E. Flynn ◽  
J. M. Zawodny ◽  
...  
Keyword(s):  
Stratospheric Ozone ◽  
Measurement Techniques ◽  
Data Sets ◽  
Data Set ◽  
Meteorological Observatory ◽  
The Stability ◽  
Combined Time Series ◽  
Relative Differences ◽  
Term Data

Abstract. The long-term evolution of stratospheric ozone at different stations in the low and mid-latitudes is investigated. The analysis is performed by comparing the collocated profiles of ozone lidars, at the northern mid-latitudes (Meteorological Observatory Hohenpeißenberg, Haute-Provence Observatory, Tsukuba and Table Mountain Facility), tropics (Mauna Loa Observatory) and southern mid-latitudes (Lauder), with ozonesondes and space-borne sensors (SBUV(/2), SAGE II, HALOE, UARS MLS and Aura MLS), extracted around the stations. Relative differences are calculated to find biases and temporal drifts in the measurements. All measurement techniques show their best agreement with respect to the lidar at 20–40 km, where the differences and drifts are generally within ±5% and ±0.5% yr−1, respectively, at most stations. In addition, the stability of the long-term ozone observations (lidar, SBUV(/2), SAGE II and HALOE) is evaluated by the cross-comparison of each data set. In general, all lidars and SBUV(/2) exhibit near-zero drifts and the comparison between SAGE II and HALOE shows larger, but insignificant drifts. The RMS of the drifts of lidar and SBUV(/2) is 0.22 and 0.27% yr−1, respectively at 20–40 km. The average drifts of the long-term data sets, derived from various comparisons, are less than ±0.3% yr−1 in the 20–40 km altitude at all stations. A combined time series of the relative differences between SAGE II, HALOE and Aura MLS with respect to lidar data at six sites is constructed, to obtain long-term data sets lasting up to 27 years. The relative drifts derived from these combined data are very small, within ±0.2% yr−1.

scholarly journals Assessment of Odin-OSIRIS ozone measurements from 2001 to the present using MLS, GOMOS, and ozonesondes

2014 ◽  
Vol 7 (1) ◽  
pp. 49-64 ◽  
Author(s):  
C. Adams ◽  
A. E. Bourassa ◽  
V. Sofieva ◽  
L. Froidevaux ◽  
C. A. McLinden ◽  
...  
Keyword(s):  
Infrared Imaging ◽  
Imaging System ◽  
Data Sets ◽  
Validation Data ◽  
Data Set ◽  
Long Term Stability ◽  
Ozone Data ◽  
The Stability ◽  
Global Mean

Abstract. The Optical Spectrograph and InfraRed Imaging System (OSIRIS) was launched aboard the Odin satellite in 2001 and is continuing to take limb-scattered sunlight measurements of the atmosphere. This work aims to characterize and assess the stability of the OSIRIS 11 yr v5.0x ozone data set. Three validation data sets were used: the v2.2 Microwave Limb Sounder (MLS) and v6 Global Ozone Monitoring by Occultation of Stars (GOMOS) satellite data records, and ozonesonde measurements. Global mean percent differences between coincident OSIRIS and validation measurements are within 5% at all altitudes above 18.5 km for MLS, above 21.5 km for GOMOS, and above 17.5 km for ozonesondes. Below 17.5 km, OSIRIS measurements agree with ozonesondes within 5% and are well-correlated (R > 0.75) with them. For low OSIRIS optics temperatures (< 16 °C), OSIRIS ozone measurements have a negative bias of 1–6% compared with the validation data sets for 25.5–40.5 km. Biases between OSIRIS ascending and descending node measurements were investigated and found to be related to aerosol retrievals below 27.5 km. Above 30 km, agreement between OSIRIS and the validation data sets was related to the OSIRIS retrieved albedo, which measures apparent upwelling, with a positive bias in OSIRIS data with large albedos. In order to assess the long-term stability of OSIRIS measurements, global average drifts relative to the validation data sets were calculated and were found to be < 3% per decade for comparisons with MLS for 19.5–36.5 km, GOMOS for 18.5–54.5 km, and ozonesondes for 12.5–22.5 km. Above 36.5 km, the relative drift for OSIRIS versus MLS ranged from ~ 0 to 6% per decade, depending on the data set used to convert MLS data to the OSIRIS altitude versus number density grid. Overall, this work demonstrates that the OSIRIS 11 yr ozone data set from 2001 to the present is suitable for trend studies.

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