scholarly journals The 2013 Earthquake Series in the Southern Vienna Basin: location

2014 ◽  
Vol 36 ◽  
pp. 77-80 ◽  
Author(s):  
M.-T. Apoloner ◽  
G. Bokelmann ◽  
I. Bianchi ◽  
E. Brückl ◽  
H. Hausmann ◽  
...  
Keyword(s):  
Depth Estimation ◽  
Velocity Model ◽  
Earthquake Intensity ◽  
Vienna Basin ◽  
Epicentral Area ◽  
Seismic Sensors ◽  
Main Shocks ◽  
Moderate Seismicity ◽  
Double Differences ◽  
Directivity Effects

Abstract. Eastern Austria is a region of low to moderate seismicity, and hence the seismological network coverage is relatively sparse. Nevertheless accurate earthquake location is very important, as the area is one of the most densely populated and most developed areas in Austria. In 2013 a series of earthquakes with magnitudes up to 4.2 was recorded in the Southern Vienna Basin. With portable broadband, semi-permanent, and permanent installed seismic sensors from different institutions it was possible to record the main- and aftershocks with an unusual multitude of close-by seismic stations. In this study we combine records from all available stations up to 240 km distance in one dataset. First, we stabilize the location with three stations deployed in the epicentral area. The higher network density moves the location of smaller magnitude events closer to the main shocks, with respect to preliminary locations achieved by permanent and semi-permanent networks. Then we locate with NonLinLoc using consistent picks, a 3-D velocity model and apply station corrections. This second approach results in stable epicenters, for limited and even changing station availability. This dataset can then be inspected more closely for the presence of regional phases, which then can be used for more accurate localizations and especially depth estimation. Further research will address directivity effects and the asymmetry in earthquake intensity observed throughout the area, using double differences and cross-correlations.

scholarly journals Modeling and detection of regional depth phases at the GERES array

2015 ◽  
Vol 41 ◽  
pp. 5-10
Author(s):  
M.-T. Apoloner ◽  
G. Bokelmann
Keyword(s):  
Array Processing ◽  
Synthetic Data ◽  
Region Of Interest ◽  
Sedimentary Basins ◽  
Depth Estimation ◽  
Vienna Basin ◽  
North West ◽  
The North ◽  
Propagation Behavior ◽  
Moderate Seismicity

Abstract. The Vienna Basin in Eastern Austria is a region of low to moderate seismicity, and hence the seismological network coverage is relatively sparse. Nevertheless, the area is one of the most densely populated and most developed areas in Austria, so accurate earthquake location, including depth estimation and relation to faults is not only important for understanding tectonic processes, but also for estimating seismic hazard. Particularly depth estimation needs a dense seismic network around the anticipated epicenter. If the station coverage is not sufficient, the depth can only be estimated roughly. Regional Depth Phases (RDP) like sPg, sPmP and sPn have been already used successfully for calculating depth even if only observable from one station. However, especially in regions with sedimentary basins these phases prove difficult or impossible to recover from the seismic records. For this study we use seismic array data from GERES. It is 220 km to the North West of the Vienna Basin, which – according to literature – is a suitable distance to recover PmP and sPmP phases. We use array processing on recent earthquake data from the Vienna Basin with local magnitudes from 2.1 to 4.2 to reduce the SNR and to search for RDP. At the same time, we do similar processing on synthetic data specially modeled for this application. We compare real and synthetic results to assess which phases can be identified and to what extent depth estimation can be improved. Additionally, we calculate a map of lateral propagation behavior of RDP for a typical strike-slip earthquake in our region of interest up to 400 km distance. For our study case RDP propagation is strongly azimuthally dependent. Also, distance ranges differ from literature sources. Comparing with synthetic seismograms we identify PmP and PbP phases with array processing as strongest arrivals. Although the associated depth phases cannot be identified at this distance and azimuth, identification of the PbP phases limits possible depth to less than 20 km. Polarization analysis adds information on the first arriving Pn wave for local magnitudes above 2.5.

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.

An integrated 3D velocity inversion—joint hypocentral determination relocation analysis of events in the Northridge area

1996 ◽  
Vol 86 (1B) ◽  
pp. S138-S155
Author(s):  
Jose Pujol
Keyword(s):  
Weighted Average ◽  
Velocity Model ◽  
Actual Data ◽  
Low Velocity ◽  
Lateral Velocity ◽  
Epicentral Area ◽  
Velocity Inversion ◽  
Station Corrections ◽  
3D Velocity Model ◽  
Velocity Zone

Abstract A subset of 3371 events recorded in the Northridge area by the Southern California Seismic Network during January to April 1994 was relocated with the joint hypocentral determination (JHD) technique. This analysis showed two unexpected results: (a) the JHD locations are shifted about 3.9 km on average in a northwest direction with respect to the locations determined using a single-event location (SEL) program, and (b) the station corrections vary between −0.55 and 1.26 sec, a rather large range. In addition, the JHD locations are less scattered than the SEL locations. For each station, the weighted average of the arrival time residuals obtained when the events are located with the SEL program (which does not apply distance or error weighting) are generally smaller than the corresponding JHD corrections. The locations determined with SEL and using the weighted average residuals as station corrections do not differ much from the SEL locations, but on average the RMS residuals become as small as those corresponding to the JHD locations. As the magnitude of the station corrections indicates the presence of large lateral velocity variations, a 3D velocity model for the area was determined using the arrival times of 1012 events recorded by at least 17 stations. The initial velocity model was that used routinely by the Southern California Earthquake Center. The first two layers (5.5- and 10.5-km thick) were subdivided into 100 blocks each (12 × 12 km). These layers show a pronounced low-velocity anomaly (24% and 16%, respectively) immediately to the northwest of the epicentral area. This low-velocity zone coincides with the west Ventura Basin. Another pronounced low-velocity zone to the southeast of the epicentral area reflects the presence of the Los Angeles Basin. The locations obtained with the 3D velocity model are consistently to the southeast of the JHD locations, 2.4 km on average. To establish the effect of these pronounced lateral velocity variations on the SEL and JHD locations, synthetic travel times were analyzed. The synthetic times were generated for event locations determined by JHD (shifted by various amounts) and the 3D velocity model and were subsequently treated as the actual data. The most important result of this analysis is that the JHD locations are affected by a quasi-systematic shift in a northwest direction (up to about 2.7 km on average, depending on the initial shift) but that the relative locations are well preserved. Therefore, both the velocity inversion of the actual data and the analysis of the synthetic data indicate that the JHD locations determined for the actual data are quasi-systematically mislocated. To account for this mislocation, an overall shift of 2.5 km to the southeast was applied to all the JHD locations. One of the most important implications of the shifted locations is the possibility that the northeasterly dipping Santa Susana fault, to the northwest of the epicentral area, was seismically active during the aftershock sequence. This feature is more diffuse in other published locations.

Advanced localization of small seismic events in Europe, case studies in Denmark, Netherlands and Iceland from the GeoERA HIKE project

2020 ◽  
Author(s):  
Tine B. Larsen ◽  
Joana E. Martins ◽  
Sigríður Kristjánsdóttir ◽  
Camilla Rasmussen ◽  
Peter H. Voss ◽  
...  
Keyword(s):  
Anthropogenic Activities ◽  
Depth Estimation ◽  
Velocity Model ◽  
The European Union ◽  
Simple Method ◽  
Small Magnitude ◽  
Velocity Models ◽  
Uncertainty Estimates ◽  
Gas Fields

<p>Earthquakes carry important information about the current state of stress in the subsurface as well as information on the location of weaknesses. Energy exploitation activities and energy storage are inherently connected to changes in pressure in the subsurface and varying pressure rates are applied depending on the level of activity. Especially rapid changes in pressure are known to lead to induced and triggered earthquakes, and in some cases lead to reactivation of otherwise stable and unknown faults. In some cases, increased small magnitude induced seismicity is an indication of possible larger events to follow.</p><p>Small earthquakes can be elusive and hard to locate precisely due to low signal-to-noise levels, an insufficient number of seismograph stations as well as over simplified methods and subsurface models. These challenges need to be overcome to be able to more accurately relate microseismicity to anthropogenic activities, and to be able to relate earthquakes to individual faults – both known faults and faults previously unknown. We explore ways to improve the hypocenter locations of earthquakes in exploited areas, principally by studying the effects of improving velocity models from standard 1D models to 3D models. When the geology is relatively uniform over the study area and the number of seismographs is abundant, using a 1D velocity model and a relatively simple method allows for fast and efficient processing yielding useful results. However, a 1D layered velocity model is not the best approximation where anisotropy is high, in areas with localized velocity anomalies, and where substantial velocity jumps in a layered medium control the differential arrival between P- and S-waves resulting in significant depth estimation uncertainties.</p><p>We present results using the NonLinLoc software for locating small earthquakes in Denmark, Netherlands and Iceland using 3D velocity models. The location method provides good uncertainty estimates on the hypocenters. To test the quality of the hypocenters calculated with 3D velocity models, results from NonLinLoc is compared to existing hypocenter solutions for the same earthquakes. The results are evaluated with respect to deviations in hypocenters, uncertainty estimates provided by the different methods, efficiency and applicability for different geological settings. The focus of the Danish case study is the oil and gas fields in the North Sea, however due to sparse data and low seismicity the entire Danish region is included in the study. For The Netherlands the focus of the case study is the two decommissioned gas fields, Roswinkel and Castricum, where seismicity occurred after the end of production. The Icelandic case study focusses on the Reykjanes geothermal field located at the southwest point of the Reykjanes Peninsula. Most activity is natural but induced activity has been recorded near the production area of the Reykjanes power plant.</p><p>The GeoERA-HIKE project has received funding from the European Union’s Horizon 2020 research and innovation programme under agreement No. 731166</p>

Rupture depths and source processes of the 1997-1998 earthquake sequence in central Italy

1999 ◽  
Vol 89 (1) ◽  
pp. 305-310
Author(s):  
Marco Olivieri ◽  
Göran Ekström
Keyword(s):  
Waveform Inversion ◽  
Central Italy ◽  
Horizontal Component ◽  
Central Apennines ◽  
Epicentral Area ◽  
Waveform Modeling ◽  
The North ◽  
Teleseismic Data ◽  
Significant Damage ◽  
Directivity Effects

Abstract The focal depths and the rupture processes of four moderate earthquakes, which occurred in central Italy during 1997 and 1998, are investigated using broadband teleseismic data. The earthquakes, the largest with MW = 6.0, caused significant damage in the epicentral area and are part of an unusual sequence of moderate-sized earthquakes to strike the central Apennines. For three of the events, the waveforms are found to be consistent with seismic ruptures confined to the top 5 to 7 km of the crust. Directivity effects are evident in the waveforms of the largest earthquake, and waveform inversion suggests an upward rupture with a horizontal component oriented toward the north. One earthquake (MW = 5.2) is confirmed from waveform modeling to have occurred at 50 km depth. This is the first event of this magnitude to have been located in the mantle beneath the Apennines.

The Relationship between Damage and Peak Accelerations in Ripabottoni during the 2002 Molise, Italy, Earthquake

2004 ◽  
Vol 20 (1_suppl) ◽  
pp. 119-130 ◽  
Author(s):  
Luana Isella ◽  
Stefano Podestà ◽  
Sonia Resemini ◽  
Marco Pasta ◽  
Claudio Eva
Keyword(s):  
Vertical Component ◽  
High Energy ◽  
Epicentral Area ◽  
Emergency Operations ◽  
Emergency Operations Center ◽  
Main Shocks ◽  
The University ◽  
The Village ◽  
The Relationship ◽  
Operations Center

After the main shocks of the 2002 Molise, Italy, earthquake sequence, the University of Genoa Geophysical Section (Dip. Te. Ris) installed a temporary seismic network, composed of two velocimetric and two accelerometric stations, in the village of Ripabottoni (Campobasso Province), near the epicentral area. These stations were implemented in the regional network of seismic instruments installed after November 1 by geophysical institutes from Rome and Trieste, Italy. The network registered more than 2,000 aftershocks with magnitudes ranging from 1.0–4.0. A DISEG Group also participated in a survey coordinated by the Larino Emergency Operations Center to examine damaged churches. The preliminary data, which correlates the waveform of the available recordings from aftershocks with damaged masonry pillars, indicates that the damage may relate not only to the intrinsic vulnerability of this building type, but also to the high energy in the high frequency range observed in the vertical component of the earthquakes.

scholarly journals Improved Resolution and Cost Performance of Low-Cost MEMS Seismic Sensor through Parallel Acquisition

Sensors ◽  
2021 ◽  
Vol 21 (23) ◽  
pp. 7970
Author(s):  
Xing-Xing Hu ◽  
Xi-Zhen Wang ◽  
Bo Chen ◽  
Cai-Hua Li ◽  
Yi-Xiang Tang ◽  
...  
Keyword(s):  
Average Method ◽  
Dynamic Range ◽  
Low Cost ◽  
Cost Effective ◽  
Earthquake Intensity ◽  
Parallel Acquisition ◽  
Building Conditions ◽  
Mems Accelerometer ◽  
Seismic Sensors ◽  
Mems Accelerometers

In earthquake monitoring, an important aspect of the operational effect of earthquake intensity rapid reporting and earthquake early warning networks depends on the density and performance of the deployed seismic sensors. To improve the resolution of seismic sensors as much as possible while keeping costs low, in this article the use of multiple low-cost and low-resolution digital MEMS accelerometers is proposed to increase the resolution through the correlation average method. In addition, a cost-effective MEMS seismic sensor is developed. With ARM and Linux embedded computer technology, this instrument can cyclically store the continuous collected data on a built-in large-capacity SD card for approximately 12 months. With its real-time seismic data processing algorithm, this instrument is able to automatically identify seismic events and calculate ground motion parameters. Moreover, the instrument is easy to install in a variety of ground or building conditions. The results show that the RMS noise of the instrument is reduced from 0.096 cm/s2 with a single MEMS accelerometer to 0.034 cm/s2 in a bandwidth of 0.1–20 Hz by using the correlation average method of eight low-cost MEMS accelerometers. The dynamic range reaches more than 90 dB, the amplitude–frequency response of its input and output within −3 dB is DC −80 Hz, and the linearity is better than 0.47%. In the records from our instrument, earthquakes with magnitudes between M2.2 and M5.1 and distances from the epicenter shorter than 200 km have a relatively high SNR, and are more visible than they were prior to the joint averaging.

scholarly journals Seismicity in colombian llanos foothills: Characterization, relocation and local seismic tomography

2015 ◽  
pp. 14-24 ◽  
Author(s):  
Francisco Javier Muñoz-Burbano ◽  
Carlos Alberto Vargas-Jiménez ◽  
German Chicangana
Keyword(s):  
Velocity Model ◽  
Fault System ◽  
Low Velocity ◽  
Simultaneous Inversion ◽  
Velocity Anomaly ◽  
3D Velocity Model ◽  
New Locations ◽  
Double Differences ◽  
Southwest Region ◽  
Santa Maria

An earthquake relocation by seismic simultaneous inversion and double differences methods were done in the Colombian Llanos Foothills from 3° to 5°N and from 73° to 75°W. The data used in this work take account 483 earthquakes registered by The Colombia National Seismological Network (RSNC) between 1993 and 2012. For the events relocation the root mean square (RMS) was reduced and several earthquake clusters were identified. The new locations shows principally at southwestern zone are related with the Eastern Frontal Fault System with faults as the Servitá-Santa Maria fault and the Algeciras Fault. In addition this work shows a 3D velocity model indicating an anomaly in the wave behavior related mainly to the low velocity zone under the Eastern Cordillera and minimum variations in average velocity toward southeast zone related with the Amazon Craton. Finally in southwest region where located the faults shows a Vp high velocity anomaly.

scholarly journals Rapid response to the Mw 4.9 earthquake of November 11, 2019 in Le Teil, Lower Rhône Valley, France

2020 ◽  
Author(s):  
Cécile Cornou ◽  
Jean-Paul Ampuero ◽  
Coralie aubert ◽  
Laurence Audin ◽  
Stéphane Baize ◽  
...  
Keyword(s):  
Focal Depth ◽  
Seismic Hazard Assessment ◽  
Normal Fault ◽  
Field Evaluation ◽  
Fault System ◽  
Seismic Unit ◽  
Epicentral Area ◽  
Massif Central ◽  
Moderate Seismicity ◽  
Rhone Valley

On November 11, 2019, a Mw 4.9 earthquake hit the region close to Montelimar (lower Rhône Valley, France), on the eastern margin of the Massif Central close to the external part of the Alps. Occuring in a moderate seismicity area, this earthquake is remarkable for its very shallow focal depth (between 1 and 3 km), its magnitude,  and the moderate to large damages it produced in several villages. InSAR interferograms indicated a shallow rupture about 4 km long reaching the surface and the reactivation of the ancient NE-SW La Rouviere normal fault in reverse faulting in agreement with the present-day E-W compressional tectonics. The peculiarity of this earthquake together with a poor coverage of the epicentral region by permanent seismological and geodetic stations triggered the mobilisation of the French post-seismic unit and the broad French scientific community from various institutions, with the deployment of geophysical instruments (seismological and geodesic stations),  geological field surveys, and field evaluation of the intensity of the earthquake. Within 7 days after the mainshock, 47 seismological stations were deployed in the epicentral area to improve the Le Teil aftershocks locations relative to the French permanent seismological network (RESIF), monitor the temporal and spatial evolution of microearthquakes close to the fault plane and temporal evolution of the seismic response of 3 damaged historical buildings, and to study suspected site effects and their influence in the distribution of seismic damage. This seismological dataset, completed by data owned by different institutions, was integrated in a homogeneous archive and distributed through FDSN web services by the RESIF data center. This dataset, together with observations of surface rupture evidences, geologic, geodetic and satellite data, will help to unravel the causes and rupture mechanism of this earthquake, and contribute to account in seismic hazard assessment for earthquakes along the major regional Cévenne fault system in a context of present-day compressional tectonics.

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