Search for: All records

As seismic data availability increases, the necessity for automated processing techniques has become increasingly evident. Expanded geophysical datasets collected over the past several decades across Antarctica provide excellent resources to evaluate different event detection approaches. We have used the traditional Short-Term Average/Long-Term Average (STA/LTA) algorithm to catalogue seismic data recorded by 19 stations in East Antarctica between 2012 and 2015. However, the complexities of the East Antarctic dataset, including low magnitude earthquakes and other types of seismic events such as icequakes or firnquakes, warrant more advanced automated detection techniques. Therefore, we have also applied template matching as well as several deep learning algorithms, including Generalized Phase Detection (GPD), PhaseNet, BasicPhaseAE, and EQTransformer (EQT), to identify seismic phases within our dataset. Our goal is not only to increase the volume of detectable seismic events but also to gain insights into the effectiveness of these different automated approaches. Our assessment evaluates the completeness of the newly generated catalogs, the precision of identified event locations, and the quality of the picks. The performance of these different event detection techniques applied to continuous seismic data from a polar environment will be highlighted. We will also identify potential limitations and necessary adjustments for deep learning algorithm training, which is essential for their reliable application to specific datasets. 

Abstract The 1886 magnitude ∼7 Summerville, South Carolina, earthquake was the largest recorded on the east coast of the United States. A better understanding of this earthquake would allow for an improved evaluation of the intraplate seismic hazard in this region. However, its source fault structure remains unclear. Starting in May 2021, a temporary 19-station short-period seismic network was deployed in the Summerville region. Here, we present our scientific motivation, station geometry, and quality of the recorded seismic data. We also show preliminary results of microearthquake detections and relocations using recordings from both our temporary and four permanent stations in the region. Starting with 52 template events, including two magnitude ∼3 events on 27 September 2021, we perform a matched filter detection with the one year of continuous data, resulting in a catalog of 181 total events. We then determine precise relative locations of a portion of these events using differential travel-time relocation methods, and compare the results with relocation results of 269 events from a previous seismic deployment in 2011–2012. We also determine focal mechanism solutions for three events from 27 September 2021 with magnitudes 2.0, 3.1, and 3.3, and infer their fault planes. Our relocation results show a south-striking west-dipping zone in the southern seismicity cluster, which is consistent with the thrust focal mechanism of the magnitude 3.3 earthquake on 27 September 2021 and results from the previous study based on the temporary deployment in 2011–2012. In comparison, the magnitudes 3.1 and 2.0 events likely occur on a north–south-striking right-lateral strike-slip fault further north, indicating complex patterns of stress and faulting styles in the region. 

Abstract We present the high-resolution Parkfield matched filter relocated earthquake (PKD-MR) catalog for the 2004 Mw 6 Parkfield earthquake sequence in central California. We use high-quality seismic data recorded by the borehole High Resolution Seismic Network combined with matched filter detection and relocations from cross-correlation derived differential travel times. We determine the magnitudes of newly detected events by computing the amplitude ratio between the detections and templates using a principal component fit. The relocated catalog spans from 6 November 2003 to 28 March 2005 and contains 13,914 earthquakes, which is about three times the number of events listed in the Northern California Seismic Network catalog. Our results on the seismicity rate changes before the 2004 mainshock do not show clear precursory signals, although we find an increase in the seismic activity in the creeping section of the San Andreas fault (SAF) (about ∼30 km northwest of the mainshock epicenter) in the weeks prior to the mainshock. We also observe a decrease in the b-value parameter in the Gutenberg–Richter relationship in the creeping section in the weeks prior to the mainshock. Our results suggest stress is increasingly released seismically in the creeping section, accompanied by a decreasing aseismic creeping rate before the mainshock occurrence. However, b-value and seismicity rates remain stable in the Parkfield section where the 2004 mainshock ruptured. This updated catalog can be used to study the evolution of aftershocks and their relations to afterslip following the 2004 Parkfield mainshock, seismicity before the mainshock, and how external stresses interact with the Parkfield section of the SAF and the 2004 sequence. 

Key Points The 15 January 2022 Hunga Tonga‐Hunga Ha'apai eruption had four episodic seismic subevents with similar waveforms within ∼300 s An unusual upward force jump‐started each subevent A magma hammer explains the force and estimates the subsurface magma mass flux which fits the vent discharge rate based on satellite data 

We investigate spatiotemporal changes of intermediate‐depth earthquakes in the double seismic zone beneath Central and Northeastern Japan before and after the 2011 magnitude 9 Tohoku earthquake. We build a template‐matching catalog 1 year before and 1 year after the Tohoku earthquake using Hi‐net recordings. The new catalog has a six‐fold increase in earthquakes compared to the Japan Meteorological Agency catalog. Our results show no significant change in the intermediate‐depth earthquake rate prior to the Tohoku earthquake, but a clear increase in both planes following the Tohoku earthquake. The regions with increased intermediate‐depth earthquake activity and the post‐seismic slips following the Tohoku earthquake are spatially separate and complementary with each other. Aftershock productivity of intermediate‐depth earthquakes increased in both planes following the Tohoku earthquake. Overall, aftershock productivity of the upper plane is higher than the lower plane, likely indicating that stress environments and physical mechanisms of intermediate‐depth earthquakes in the two planes are distinct.

 

The Salton Sea Geothermal Field (SSGF) is one of the most seismically active and geothermally productive fields in California. Here we present a detailed analysis of short-term seismicity change in SSGF from 2008 to 2013 during and right following large distant earthquakes, as well as long-term seismicity change due to geothermal productions. We first apply a GPU-based waveform matched-filter technique (WMFT) to the continuous data recorded by the Calenergy Borehole (EN) Network and detect more than 70 000 new micro-earthquakes than listed in the standard Southern California Seismic Network catalogue. We then analyse the seismicity rate changes in the SSGF associated with transient stress fluctuations triggered by regional and large teleseismic earthquakes from 1999 to 2019. We find triggered seismicity in the SSGF following seven regional M > 5.5 earthquakes. In comparison, most teleseismic earthquakes with M > 8.0 did not trigger significant seismicity rate change in the SSGF, likely indicating a frequency dependence in remote dynamic triggering. We further characterize the correlation between the long-term seismicity rate and geothermal production rates, and the temporal and spatial distribution of Guttenberg–Richter b-values inside and outside the SSGF with the newly detected catalogue. The long-term seismicity shows that events with M > 1.5 are likely correlated with net production rates, while smaller events do not show any correlation. The b-values inside the SSGF are higher than those outside the SSGF, and the locations of dynamically triggered events are close to locations with high b-values.

 

We present our estimations and comparisons of the in situ Vp/Vs ratios and seismicity characteristics for the Parkfield segment of the San Andreas fault in northern California and the San Jacinto Fault Zone and its adjacent regions in southern California. Our results show that the high-resolution in situ Vp/Vs ratios are much more complex than the tomographic Vp/Vs models. They show similar variation patterns to those in the tomographic Vp models, indicating that Vp/Vs ratios are controlled by material properties but are also strongly influenced by fluid contents. In Parkfield, we observe velocity contrasts between the creeping and locked sections. In southern California, we see small-scale anomalous Vp/Vs variation patterns, especially where fault segments intersect, terminate and change orientations. In addition, our investigation confirms that the seismicity in Parkfield is more repeatable than in southern California. However, the earthquakes in the southernmost portion of the San Andreas fault, the trifurcation area of the San Jacinto Fault Zone and the Imperial fault are as much likely falling into clusters as those in Parkfield. The correlation of highly similar events with anomalous in situ Vp/Vs ratios supports the important role of fluids in the occurrence of repeating earthquakes. The high-resolution Vp/Vs ratio estimation method and the corresponding results are helpful for revealing roles of fluids in driving earthquake, fault interaction and stress distribution in fault zones.

 

Abstract Recent studies have shown that the Antarctic cryosphere is sensitive to external disturbances such as tidal stresses or dynamic stresses from remote large earthquakes. In this study, we systematically examine evidence of remotely triggered microseismicity around Mount (Mt.) Erebus, an active high elevation stratovolcano located on Ross Island, Antarctica. We detect microearthquakes recorded by multiple stations from the Mt. Erebus Volcano Observatory Seismic Network one day before and after 43 large teleseismic earthquakes, and find that seven large earthquakes (including the 2010 Mw 8.8 Maule, Chile, and 2012 Mw 8.6 Indian Ocean events) triggered local seismicity on the volcano, with most triggered events occurring during the passage of the shorter-period Rayleigh waves. In addition, their waveforms and locations for the triggered events are different when comparing with seismic events arising from the persistent small-scale eruptions, but similar to other detected events before and after the mainshocks. Based on the waveform characteristics and their locations, we infer that these triggered events are likely shallow icequakes triggered by dilatational stress perturbations from teleseismic surface waves. We show that teleseismic earthquakes with higher peak dynamic stress changes are more capable of triggering icequakes at Mt. Erebus. We also find that the icequakes in this study are more likely to be triggered during the austral summer months. Our study motivates the continued monitoring of Mount Erebus with dense seismic instrumentation to better understand interactions between dynamic seismic triggering, crospheric processes, and volcanic activity.