Extended Observations and New Insights of Dynamically Triggered Tremor in Parkfield

<p>We create an extended catalog of dynamically triggered tremor in the Parkfield region of the San Andreas Fault for teleseismic and regional earthquakes from 2001-2020 with a magnitude threshold of M >7. After selection of clear dynamic triggering episodes, each tremor event is precisely located using a multi station approach. Using this new catalog of triggered tremor, we quantitatively evaluate the conditions under which tremor is triggered. In particular, we study the effect of frequency dependent peak dynamic strain, peak ground velocity, and the incident azimuth of triggering waves. We further try to assess if the triggering potential in the San Andreas Fault evolves as function of time. Finally, we search for differences and similarities (e.g. frequency content, location) between triggered and regular tremor. Our observations provide new insights about the physical conditions necessary for triggering tremor, and in general, on the physical processes generating non-volcanic tremors.</p>

Tectonic tremors in the Northern Mexican subduction zone remotely triggered by the 2017 Mw8.2 Tehuantepec earthquake

Surface waves from the 2017 Mw8.2 Tehuantepec earthquake remotely triggered tectonic tremors in the Jalisco region, approximately 1000 km WNW in the northern Mexican subduction zone. This is the first observation of tremor triggering in this region and one of the largest known examples of a triggered tremor in the world. Although prior studies have found tectonic tremors triggered by teleseismic waves in subduction zones and plate boundaries, further investigation of tremor triggering is crucially important for understanding the causative mechanism. We calculate the stress and strain changes across the three-dimensional plate interface attributable to seismic waves from the earthquake by full wavefield simulation. The maximum magnitude of the dynamic strain tensor eigenvalues on the plate interface, where tremors likely occur, is approximately 10–6. The subducting slab geometry effectively amplifies triggering waves. The triggering Coulomb failure stress changes resolved for a thrust fault plane consistent with the geometry are estimated to be approximately 10–40 kPa. The relationship between the triggering stress and triggered tremor amplitude may indicate that the aσ of the rate–state-dependent friction law is 10–100 kPa.

Tectonic Tremors in the Northern Mexican Subduction Zone Remotely Triggered by the 2017 Mw8.2 Tehuantepec Earthquake

Surface waves from the 2017 Mw8.2 Tehuantepec earthquake remotely triggered tectonic tremors in the Jalisco region, approximately 1000 km WNW in the northern Mexican subduction zone. This is the first observation of tremor triggering in this region and one of the largest known examples of a triggered tremor in the world. Although prior studies have found tectonic tremors triggered by teleseismic waves in subduction zones and plate boundaries, further investigation of tremor triggering is crucially important for understanding the causative mechanism. We calculate the stress and strain changes across the three-dimensional plate interface attributable to seismic waves from the earthquake by full wavefield simulation. The maximum magnitude of the dynamic strain tensor eigenvalues on the plate interface, where tremors likely occur, is approximately 10 -6 . The subducting slab geometry effectively amplifies triggering waves. The triggering Coulomb failure stress changes resolved for a thrust fault plane consistent with the geometry are estimated to be approximately 10-40 kPa. The relationship between the triggering stress and triggered tremor amplitude may indicate that the [[EQUATION]] of the rate-state-dependent friction law is 10 to 100 kPa.

Tectonic Tremors in the Northern Mexican Subduction Zone Remotely Triggered by the 2017 Mw8.2 Tehuantepec Earthquake

Surface waves from the 2017 Mw8.2 Tehuantepec earthquake remotely triggered tectonic tremors in the Jalisco region, approximately 1000 km WNW in the northern Mexican subduction zone. This is the first observation of tremor triggering in this region and one of the largest known examples of triggered tremor in the world. While prior studies found tectonic tremors triggered by teleseismic waves in subduction zones and plate boundaries, further investigation of tremor triggering is crucially important for understanding the causative mechanism. We calculate the stress and strain changes across the three-dimensional plate interface attributable to seismic waves from the earthquake by full wavefield simulation. The maximum magnitude of the dynamic strain tensor eigenvalues on the plate interface, where tremors likely occur, is approximately 10-6. The subducting slab geometry effectively amplifies triggering waves. The triggering Coulomb failure stress changes resolved for a thrust fault plane consistent with the geometry are estimated at approximately 10-40 kPa. The relationship between the triggering stress and triggered tremor amplitude may indicate that the aσ of the rate-state-dependent friction law is 10 to 100 kPa.

Isolated Triggered Tremor Spots in South America and Implications for Global Tremor Activity

ABSTRACT We report new observations of triggered tectonic tremor in three regions in South America along the plate boundary between the Nazca and South America plates: southern Chile, Ecuador, and central Colombia. In these regions, tremor was observed during the passage of large‐amplitude surface waves of recent large earthquakes, which occurred in South America and around the world. In southern Chile, triggered tremor was observed around an ambient tremor active zone in the Chile triple junction region. In Ecuador and central Colombia, only one seismic station in each region recorded triggered tremor. With a single‐station approach, we are able to estimate potential tremor sources in these regions. Triggered tremor in Ecuador is likely associated with an inland fault near the volcanic region. In central Colombia, triggered tremor may be associated with the Romeral fault system rather than the subduction zone interface. In addition, we summarize global observations of tremor‐triggering stress and background ambient tremor activity in 24 tremor‐active regions. Based on the global summary of triggered and ambient tremor activity, the relative lack of triggered tremor in central and northern Chile and Peru is consistent with the lack of background tremor activity in these regions, suggesting tectonic tremor occurs only in isolated regions along major faults.