Monitoring and analysis of seismic data during the 2018 sunda strait tsunami

The tsunami of Sunda Strait occurred on December 22, 2018, at 21:03 West Indonesia Time (zone). An eruption of Mount Anak Krakatau caused an eruption that triggered a landslide on the slopes of Mount Anak Krakatau covering an area of 64 hectares that hit the coastal area of western Banten and southern Lampung and resulted in 437 deaths, 14.059 people were injured, and 33.721 people were displaced. Before the tsunami, signal transmissions (gaps) at the Lava seismograph station installed on the body of Mount Anak Krakatau experienced broken so that Mount Anak Krakatau Observation Post could not record volcanic earthquake signals since December 22, 2018, at 21.03 West Indonesia Time (zone). Given these facts, proper monitoring and analysis were required to monitor and analyze the source of ground vibrations originating from the eruption of Mount Anak Krakatau. Therefore, this study aims to confirm the eruptive activity of Mount Anak Krakatau based on seismic monitoring and analysis sourced from the BMKG's seismic sensor network. The method the author uses is by monitoring the seismic signal recorded by the seismometer and analyzing the seismic signal using the Seiscomp3 software. By the results of monitoring and analysis of seismic data, it was found that the location of the center of the ground shaking was on Mount Anak Krakatau with a magnitude of 3.4, and a depth of 1 km. To anticipate similar tsunami events in the future, it is very necessary to have a tsunami early warning system originating from volcanic activity and volcanic body avalanches.

Further studies on the 1988 MW 5.9 Saguenay, Quebec, earthquake sequence

Many small earthquakes occur annually in Eastern Canada, but moderate to strong earthquakes are infrequent. The 25 November 1988 MW 5.9 Saguenay mainshock remains the largest earthquake in the last 80 years in eastern North America. In this article, some aspects of that earthquake sequence were re-analyzed using several modern methods. The regional depth-phase modeling procedure was used to refine the focal depths for the foreshock, the aftershocks, and other MN ≥ 2.5 regional earthquakes. The hypocenters of 10 earthquakes were relocated using hypoDD. The spatial distribution of eight relocated hypocenters defines the rupture plane of the mainshock. The moment tensor for the mainshock was retrieved using three-component long-period surface wave records at station HRV (Harvard seismograph station) with additional constraints from P-wave polarities. One nodal plane is conclusively identified to be close to the rupture plane, and its strike is similar to the trend of the south wall of the Saguenay Graben. Based on the consistency between the strike of the nodal plane and the trend of the Graben, as well as the deep focal depth distribution, we suggest that the Saguenay earthquake sequence is related to the reactivation of one of the faults of the Saguenay Graben.

Vibroseis recording techniques and data reduction from the Jemez Tomography Experiment

The Jemez Tomography Experiment (JTEX) is a multidisciplinary study focused on the Valles Caldera and the Jemez Mountains, New Mexico. The objectives of the project are to create a high resolution crustal model of the subsurface structure of this silicic volcanic system and to develop an interpretation of its volcanic evolution. Use of Vibroseis sources in the acquisition of refraction/wide-angle reflection seismic data provided challenges beyond conventional explosive-source data. Processing of the JTEX Vibroseis data is an involved procedure consisting of sorting, cross-correlating, filtering, and stacking numerous individual seismograms in the production of final record sections. However, excellent results (high signal-to-noise seismograms at relatively small spacings) are obtainable with coherent arrivals at source-receiver distances of more than 60 km. The primary drawback in this approach lies in the massive volume of data that is necessary to produce record sections. One benefit of the Vibroseis source used during JTEX was a method to decrease effective seismogram spacing. This technique, dubbed a “source-offset” technique, provides smaller overall seismograph station spacing by moving the Vibroseis sources during acquisition and leaving deployed seismographs stationary. After station corrections, this method effectively decreases station spacings and increases detail in resulting record sections. Various shallow crustal heterogeneities create travel-time advances and delays that affect the source-offset data differently than single-source data. Synthetic modeling demonstrates small travel-time discrepancies associated with the source-offset technique. However, the addition of traces with smaller station intervals clarifies secondary arrivals within record sections and aids in interpretation of these arrivals with a minimum amount of field effort required.

Detecting local and regional seismic events using the data-adaptive method at the VAF seismograph station in Finland

The data-adaptive autoregressive (hereafter DA) method was used to detect local and regional seismic events using digital data from the Vaasa (VAF) station with co-ordinates (62.3°N, 22.2°E) in western Finland. The seismic signal and the noise were assumed to have been normally distributed stochastic processes with a zero mean. The parameters of these processes were then adapted on the change of the registered signal as a function of time within a predefined detection window. The accuracy of the method presented is compared with the STA/LTA and visual methods. When the same detection threshold was used with the DA detector and the STA/LTA detector, it was found that the DA detector was more precise in detecting the onsets of seismic events. Bandpass (1.5 to 20 Hz) filtering was used in all the events discussed. This was done to reject the long-period microseismic noise. In one case, the detector was used on nonfiltered as well as filtered data, in order to show coinciding results.

Instrumental group delay for high-frequency and teleseismic P waves

The instrumental group delay dθ/dω is considered here. First, these delays were calculated for three different recording systems that were used in a precise travel-time monitoring experiment where the delays varied between 10 and 40 msec for the high frequencies of the seismograms involved. A technique is demonstrated by which these delays may be readily accounted for and by which instrumental malfunctions can be readily detected. Second, two of these systems are also currently used for the recording of short-period teleseisms; at the 1-sec period, the group delays are from 0.3 to 0.4 sec, which is significant and must be accounted for. This is particularly important when these systems are used in connection with data from other systems that have different delays, such as the World-Wide Seismograph Station Network and Canadian Seismograph Network stations. Neglecting these delays will create serious problems in seismological tomography and earthquake catalogs. Third, for long-period phases recorded by the SRO-type instruments, the delays for the 10- to 20-sec periods are 6 to 12 sec; again, these are significant and must be accounted for.

Sensitivity of Kansas Microearthquake Network

This study explores the magnitude-versus-distance sensitivity of the Kansas Geological Survey (KGS) microearthquake network. The ability of each seismograph station to record earthquakes of various magnitudes as a function of epicentral distance is investigated, and a series of magnitude-versus-distance graphs results. The ability of the network to monitor seismic activity in eastern Kansas is excellent to magnitude 1.5 and is sufficient to detect events greater than magnitude 2.3 in western Kansas. Station detection radii for magnitude 1.5 events range from 145 km for the Emporia seismograph station (EMK) to 225 km at Tuttle Creek (TCK); and for a magnitude 2 event, from 245 km at EMK to 385 km at TCK. The sensitivities of the nine seismographs of the network are similar despite their widespread locations across eastern Kansas.