Well-resolved hypocenter distribution using the double-difference relocation method in the region of the 2007 Chuetsu-oki Earthquake

A dense microseismic network was installed in Northwestern Greece for a period of eleven months. A total of 1368 events were recorded and located using a 1D model. These events were also used to derive a 3D velocity model for the area. This work presents results from further processing of the data using (a) simple location method of events in a 1D medium through Hypo71 standard procedure; (b) location via the probabilistic, non-linear earthquake location method in 3D medium; (c) relocation of the events using the Double - Difference method in 1D medium; and (d) the same relocation procedure invoking 3D medium. The application of different location methodologies results in slightly different locations, which are evaluated using as criterion the compactness of hypocenter distribution. The three point method was used in order to derive linear characteristics from the hypocenter distribution and the final results were compared against the focal mechanisms of the events as computed using the polarity method and the 3D velocity model. The combination of accurately computed hypocenters and focal mechanisms provides important information for the seismotectonics of Epirus

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Explaining Dioscorides' "Double Difference": Why Are Some Mushrooms Poisonous, and Do They Signal Their Unprofitability?

The American Naturalist ◽

10.2307/3491237 ◽

2005 ◽

Vol 166 (6) ◽

pp. 767

Author(s):

Sherratt ◽

Wilkinson ◽

Bain

Keyword(s):

Double Difference

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Supplemental Material: Geophysical analysis of the 30 July 1972 Sitka, Alaska, earthquake sequence

10.1130/geos.s.12041772.v2 ◽

2020 ◽

Author(s):

Juan A. Ochoa Chavez ◽

Diane Doser

Keyword(s):

Earthquake Sequence ◽

Double Difference ◽

Alaska Earthquake

Supplemental Material 1 contains relocated aftershocks of 30 July 1972 sequence. Supplemental Material 2 contains relocation parameters used in double-difference algorithm (HYPODD).<br>

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The Effects of Employment on Depression and Life Satisfaction Among Old-Aged Using the DD Method Combined With PSM

Innovation in Aging ◽

10.1093/geroni/igaa057.1315 ◽

2020 ◽

Vol 4 (Supplement_1) ◽

pp. 408-408

Author(s):

Si Young Song ◽

Hey Jung Jun ◽

Sun Ah Lee

Keyword(s):

Life Satisfaction ◽

Propensity Score ◽

Propensity Score Matching ◽

Multiple Regression ◽

Propensity Scores ◽

Panel Study ◽

Double Difference ◽

Combined Model ◽

Comparative Group ◽

Experimental Group

Abstract The purpose of this study is to explore the effect of employment on depression and life satisfaction among old-aged. Using 12th (2017) wave and 13th (2018) wave of Korean Welfare Panel Study (KoWePS), three stages of analyses were conducted. First, through propensity score matching (PSM) method, sample with similar propensity scores was matched between the group that did not work in 12th wave but worked in 13th wave (experimental group, N=180), and the group that did not work in 12th and 13th wave (comparative group, N=180). Second, the matched sample was used to conduct multiple regression analysis with the group dummy variable (experimental group, comparative group) as an independent variable, and depression and life satisfaction as the dependent variables. Third, combined model of propensity score matching (PSM) and double difference (DD) method was conducted to more appropriately derive the net effect of employment. The results of multiple regression after propensity matching showed that employment had a positive effect on reducing depression (B= -1.70, p< .01) and increasing life satisfaction (B= .12, p< .01) in old-aged. Furthermore, in combined model of PSM and DD, life satisfaction was improved when employed compared to non-employed (B= .15, p< .05). The results of this study are meaningful in that the meaning of employment in old-aged is more clearly derived by solving selection bias and endogenous problems. Also, this study may provide reference for establishing welfare policies related to employment among old-aged.

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Characteristics of relocated hypocenters of the 2018 M6.7 Hokkaido Eastern Iburi earthquake and its aftershocks with a three-dimensional seismic velocity structure

Earth Planets and Space ◽

10.1186/s40623-019-1100-0 ◽

2019 ◽

Vol 71 (1) ◽

Cited By ~ 1

Author(s):

Saeko Kita

Keyword(s):

Seismic Velocity ◽

Three Dimensional ◽

Double Difference ◽

Earthquake Catalog ◽

Seismic Structure ◽

Depth Limit ◽

High Attenuation ◽

South Central ◽

Collision Zone ◽

Hidaka Collision Zone

AbstractI relocated the hypocenters of the 2018 M6.7 Hokkaido Eastern Iburi earthquake and its surrounding area, using a three-dimensional seismic structure, the double-difference relocation method, and the JMA earthquake catalog. After relocation, the focal depth of the mainshock became 35.4 km. As previous studies show, in south-central Hokkaido, the Hidaka collision zone is formed, and anomalous deep and thickened forearc crust material is subducting at depths of less than 70 km. The mainshock and its aftershocks are located at depths of approximately 10 to 40 km within the lower crust of the anomalous deep and thickened curst near the uppermost mantle material intrusions in the northwestern edge of this Hidaka collision zone. Like the two previous large events, the aftershocks of this event incline steeply eastward and appear to be distributed in the deeper extension of the Ishikari-teichi-toen fault zone. The highly inclined fault in the present study is consistent with a fault model by a geodetic analysis with InSAR. The aftershocks at depths of 10 to 20 km are located at the western edge of the high-attenuation (low-Qp) zone. These kinds of relationships between hypocenters and materials are the same as the 1970 and 1982 events in the Hidaka collision zone. The anomalous large focal depths of these large events compared with the average depth limit of inland earthquakes in Japan could be caused by the locally lower temperature in south-central Hokkaido. This event is one of the approximately M7 large inland earthquakes that occurred repeatedly at a recurrence interval of approximately 40 years and is important in the collision process in the Hidaka collision zone.

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The 25 October, 2018 Zakynthos (Greece) earthquake: seismic activity at the transition between a transform fault and a subduction zone.

Geophysical Journal International ◽

10.1093/gji/ggaa575 ◽

2020 ◽

Author(s):

P Papadimitriou ◽

V Kapetanidis ◽

A Karakonstantis ◽

I Spingos ◽

K Pavlou ◽

...

Keyword(s):

Spatial Clustering ◽

Accretionary Prism ◽

Velocity Model ◽

Strike Slip ◽

Double Difference ◽

Strain Partitioning ◽

Transform Fault ◽

Fault Plane Solutions ◽

The North ◽

Waveform Modelling

Summary The properties of the Mw = 6.7 earthquake that took place on 25 October 2018, 22:54:51 UTC, ∼50 km SW of the Zakynthos Island, Greece, are thoroughly examined. The main rupture occurred on a dextral strike-slip, low-angle, east-dipping fault at a depth of 12 km, as determined by teleseismic waveform modelling. Over 4000 aftershocks were manually analysed for a period of 158 days. The events were initially located with an optimal 1D velocity model and then relocated with the double-difference method to reveal details of their spatial distribution. The latter spreads in an area spanning 80 km NNW-SSE and ∼55 km WSW-ENE. Certain parts of the aftershock zone present strong spatial clustering, mainly to the north, close to Zakynthos Island, and at the southernmost edge of the sequence. Focal mechanisms were determined for 61 significant aftershocks using regional waveform modelling. The results revealed characteristics similar to the mainshock, with few aftershocks exhibiting strike-slip faulting at steeper dip angles, possibly related to splay faults on the accretionary prism. The slip vectors that correspond to the east-dipping planes are compatible with the long-term plate convergence and with the direction of coseismic displacement on the Zakynthos Island. Fault-plane solutions in the broader study area were inverted for the determination of the regional stress-field. The results revealed a nearly horizontal, SW-NE to E-W-trending S1 and a more variable S3 axis, favouring transpressional tectonics. Spatial clusters at the northern and southern ends of the aftershock zone coincide with the SW extension of sub-vertical along-dip faults of the segmented subducting slab. The mainshock occurred in an area where strike-slip tectonics, related to the Cephalonia Transform Fault and the NW Peloponnese region, gradually converts into reverse faulting at the western edge of the Hellenic subduction. Plausible scenarios for the 2018 Zakynthos earthquake sequence include a rupture on the subduction interface, provided the slab is tilted eastwards in that area, or the reactivation of an older east-dipping thrust as a low-angle strike-slip fault that contributes to strain partitioning.

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A Single-Difference Multipath Hemispherical Map for Multipath Mitigation in BDS-2/BDS-3 Short Baseline Positioning

Remote Sensing ◽

10.3390/rs13020304 ◽

2021 ◽

Vol 13 (2) ◽

pp. 304

Author(s):

Chao Liu ◽

Yuan Tao ◽

Haiqiang Xin ◽

Xingwang Zhao ◽

Chunyang Liu ◽

...

Keyword(s):

Satellite System ◽

Observation Time ◽

Double Difference ◽

Observation Data ◽

Multipath Mitigation ◽

Short Baseline ◽

Independent Variables ◽

Positioning Errors ◽

Single Difference ◽

Repeat Time

The BeiDou Navigation Satellite System (BDS) features a heterogeneous constellation so that it is difficult to mitigate the multipath in the coordinate-domain. Therefore, mitigating the multipath in the observation-domain becomes more important. Sidereal filtering is commonly used for multipath mitigation, which needs to calculate the orbit repeat time of each satellite. However, that poses a computational challenge and damages the integrity at the end of the multipath model. Therefore, this paper proposes a single-difference model based on the multipath hemispherical map (SD-MHM) to mitigate the BDS-2/BDS-3 multipath in a short baseline. The proposed method is converted from double-difference residuals to single-difference residuals, which is not restricted by the pivot satellite transformation. Moreover, it takes the elevation and the azimuth angles of the satellite as the independent variables of the multipath model. The SD-MHM overcomes the unequal observation time of some satellites and does not require specific hardware. The experimental results show that the SD-MHM reduces the root mean square of the positioning errors by 56.4%, 63.9%, and 67.4% in the east, north, and vertical directions; moreover, it contributes to an increase in the baseline accuracy from 1.97 to 0.84 mm. The proposed SD-MHM has significant advantages in multipath mitigation compared with the advanced sidereal filtering method. Besides, the SD-MHM also features an excellent multipath correction capability for observation data with a period of more than seven days. Therefore, the SD-MHM provides a universal strategy for BDS multipath mitigation.

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Insights into Mechanical Properties of the 1980 Irpinia Fault System from the Analysis of a Seismic Sequence

Geosciences ◽

10.3390/geosciences11010028 ◽

2021 ◽

Vol 11 (1) ◽

pp. 28

Author(s):

Gaetano Festa ◽

Guido Maria Adinolfi ◽

Alessandro Caruso ◽

Simona Colombelli ◽

Grazia De Landro ◽

...

Keyword(s):

Mechanical Properties ◽

Early Warning Systems ◽

Fault System ◽

Minimum Size ◽

Double Difference ◽

Warning Systems ◽

Initiation Mechanism ◽

Earthquake Early Warning Systems ◽

The One

Seismic sequences are a powerful tool to locally infer geometrical and mechanical properties of faults and fault systems. In this study, we provided detailed location and characterization of events of the 3–7 July 2020 Irpinia sequence (southern Italy) that occurred at the northern tip of the main segment that ruptured during the 1980 Irpinia earthquake. Using an autocorrelation technique, we detected more than 340 events within the sequence, with local magnitude ranging between −0.5 and 3.0. We thus provided double difference locations, source parameter estimation, and focal mechanisms determination for the largest quality events. We found that the sequence ruptured an asperity with a size of about 800 m, along a fault structure having a strike compatible with the one of the main segments of the 1980 Irpinia earthquake, and a dip of 50–55° at depth of 10.5–12 km and 60–65° at shallower depths (7.5–9 km). Low stress drop release (average of 0.64 MPa) indicates a fluid-driven initiation mechanism of the sequence. We also evaluated the performance of the earthquake early warning systems running in real-time during the sequence, retrieving a minimum size for the blind zone in the area of about 15 km.

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