[1] The high elevation of the southern Puna plateau, the widespread melting of its crust, the gap in intermediate depth seismicity and the recent eruptions of ignimbrite complexes can be explained by delamination of the lithospheric mantle beneath it. To test this hypothesis, an array consisting of 73 broad band and short period seismic stations was deployed in the region for a period of 2 years starting in 2007. We inverted the data using the two plane wave approach and obtained 1-D and 3-D Rayleigh wave phase velocities. Our dispersion curve shows that at short periods (<70 s) the phase velocities are slightly higher than those of the Tibetan plateau and lower than those of the Anatolian plateau. At periods of 100-140 s we observe a low velocity zone that might be remnant hot asthenosphere below a flat slab (7-10 Ma). We estimate the average continental lithosphere thickness for the region to be between 100 and 130 km. Our three-dimensional Rayleigh wave phase velocities show a high velocity anomaly at low frequencies (0.007, 0.008, and 0.009 Hz) slightly to the north of Cerro Galan. This would be consistent with the hypothesis of delamination in which a piece of lithosphere has detached and caused upwelling of hot asthenosphere, which in turn caused widespread alkaline-collision related volcanism. This interpretation is also corroborated by our shear wave velocity model, where a high velocity anomaly beneath the northern edge of Cerro Galan at 130 km depth is interpreted as the delaminated block on top of the subducting Nazca slab.

We compare current and historic seismicity rates in six States in the USA and three Provinces in Canada to past and present hydrocarbon production. All States/Provinces are major hydrocarbon producers. Our analyses span three to five decades depending on data availability. Total hydrocarbon production has significantly increased in the past few years in these regions. Increased production in most areas is due to large‐scale hydraulic fracturing and thus underground fluid injection. Furthermore, increased hydrocarbon production generally leads to increased water production, which must be treated, recycled, or disposed of underground. Increased fluid injection enhances the likelihood of fault reactivation, which may affect current seismicity rates. We find that increased seismicity in Oklahoma, likely due to salt‐water disposal, has an 85% correlation with oil production. Yet, the other areas do not display State/Province‐wide correlations between increased seismicity and production, despite 8–16‐fold increases in production in some States. However, in various cases, seismicity has locally increased. Multiple factors play an important role in determining the likelihood of anthropogenic activities influencing earthquake rates, including (i) the near‐surface tectonic background rate, (ii) the existence of critically stressed and favorably oriented faults, which must be hydraulically connected to injection wells, (iii) the orientation and magnitudes of the in situ stress field, combined with (iv) the injection volumes and implemented depletion strategies. A comparison with the seismic hazard maps for the USA and Canada shows that induced seismicity is less likely in areas with a lower hazard. The opposite, however, is not necessarily true.

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Attenuation images are obtained from 6287 t-star spectral measurements of P-wave microseismic events in a mine setting. The resulting three-dimensional quality factor (Q) model reveals that most of the study region is characterized by low Q values or high attenuation (Q<25), probably caused by cavities and fractures due to mining activities. Q values between 25 and 50 show a high spatial correlation with the location of an ore deposit. Furthermore, high quality ore deposits correlate with Q values of about 45-50 whereas the low quality ore correlates with Q values of around 30. Q values of less than 10 correlate with the observed seismic cloud epicenters. These features were previously partially resolved by velocity tomography. Therefore a joint interpretation is very important in determining the lithological properties and physical state of both, the region containing the seismic epicenters and the region with the ore deposits. The same methodology is applicable to microseismic data recorded during hydraulic fracturing treatment and may give more insight into fracture density of hydrocarbon reservoirs.