Hi @Masoud264880 - welcome to the forums
The ADS1115 ADC is a 4 channel amplifier. To use with a geophone requires 2x channels (to take a differential measurement)
That means each ADS1115 could support 2x geophones.
To add more geophones requires additional ADS1115 ADCs, which can be added to the same I2C bus by setting a new address. Each ADS1115 requires a unique address so the Pi can talk to it individually.
Soldering the A0 jumper will allow connecting a second ADC to the I2C bus (with address 0x49) for a maximum of 4x geophones.
The python code has no waits or sleeps. When you read from i2c, does it wait for the next reading before continuing? ie its however-many samples per sec (Hz), so how do you ensure you read each sample and not double-read or miss a sample?